qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
values |
|---|---|---|---|---|---|
52,498 | [
"https://stats.stackexchange.com/questions/52498",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/21395/"
] | I am using Weka 3.6 to do Association Rule mining. In our data set, each transaction is a word, and each letter in the word is an item. The rules that we are mining would be in the format of <code>{a set of letters} -> {another set of letters}</code>.
So far, I have formatted six transactions by representing the ... | you can try this:
<pre><code> @RELATION ITEMS
@ATTRIBUTE itemM {?,1}
@ATTRIBUTE itemO {?,1}
@ATTRIBUTE itemN {?,1}
@ATTRIBUTE itemK {?,1}
@ATTRIBUTE itemE {?,1}
@ATTRIBUTE itemY {?,1}
@ATTRIBUTE itemU {?,1}
@ATTRIBUTE itemD {?,1}
@ATTRIBUTE itemA {?,1}
@ATTRIBUTE itemC {?,1}
@ATTRIBU... | I'm not sure if there is a more formal way of doing this, but replacing the <code>'0'</code> values with <code>?</code> works for me.
Using the following <code>.arff</code> file works for me:
<pre><code>@relation transactions
@attribute A {'1','0'}
@attribute C {'1','0'}
@attribute D {'1','0'}
@attribute E {'1','0'}
... | https://stats.stackexchange.com |
20,468 | [
"https://electronics.stackexchange.com/questions/20468",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5780/"
] | I'd like to control a couple ac fans running on mains voltage (US) using a potentiometer. I believe they're in parallel but I'm not certain. Each fan is rated at 15/13 watts @ 115 volts.
What's the best way to do this, preferably by dismantling broken appliances?
| <strong>If you mean that you want to control the speed of an AC fan with a potentiometer,<br>
it is probably not possible.</strong>
Whether an AC "mains" fan can be speed controlled with a pot depends on the technology used.<br>
Motor type is liable to be
<ul>
<li>"shaded pole" induction motor. Smaller fans used ... | You will need a dimmer circuit like on the page below, which will translate your potentiometer position to proper AC output for your fans.
<code>www.epanorama.net/documents/lights/lightdimmer.html</code>
(Note: The above link is now deliberately not "clickable". It contains three dimmer circuits (unsure which... | https://electronics.stackexchange.com |
115,902 | [
"https://security.stackexchange.com/questions/115902",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/96268/"
] | Lets say i want to make some WiFi router out of service.
I can connect to the router and close the WiFi connection or change the password.
But in this case i need to have full access to the router.
But if i don't have access to the router ( i mean that i don't have password )
==> is it possible to damage it in s... | You can deauthenticate users.
With aireplay-ng this makes users disassociate with the router denying them the service
This with the option -0
So
<pre><code>Aireplay-ng
-0 [how many packets you wannt to send] \
-a [mac of ap] \
-c [mac of client you want to deauthenticate] \
[interface]
</code></pr... | If you are connected to the router you can do it with a DDOS attack if it doesn't have a firewall or it is disabled. On the other side a router normally drops malicious packets sent to it but if it doesn't have a performing CPU and you send a lot of them, it can't analyze all packets and a service disruption will happe... | https://security.stackexchange.com |
35,685 | [
"https://dsp.stackexchange.com/questions/35685",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/24933/"
] | Say we have an integrator $y(t)= \int_{- \infty}^{t} x(t) dt$
It is incorrect to use the following method to determine if it is time variant/invariant?
First, when we have input signal $x(t),$
$y_1(t)= \int_{- \infty}^{t} x(t) dt$
Then, we shift $y(t)$ by $t_0$
$y_1(t-t_0)=\int_{- \infty}^{t-t_0} x(\tau-t_0) d\ta... | You have an answer right now, but if you want to see it using the time-shifting approach, you should do like this:
First consider the input-output relationship
$$x_1(t)\mapsto y_1(t)=\int_{-\infty}^{t}x_1(\tau)d\tau$$
Then consider the output to the shifted input:
$$x_2(t)=x_1(t-t_0)\mapsto y_2(t)=\int_{-\infty}^{t}... | This is not correct. First, you have to write it like that:
$$
\begin{align}
y(t) = \int_{-\infty}^t x(\tau)d\tau
\end{align}
$$
I.e. your variable in the integrand is different from the integral limits. Accordingly, your calculation will be different, as you will only replace $t$ with $t-t_0$ and not $\tau$.
| https://dsp.stackexchange.com |
111,226 | [
"https://softwareengineering.stackexchange.com/questions/111226",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/30302/"
] | How would you test a developer that claims to have *nix shell experience (just to be clear, we don't want to test if someone can develop on *nix, only that they know their way around the command line).
I was thinking about making them solve a problem of getting information out of log files, which would involve some ba... | From my personal experience developer working on an *nix system needs to know:
<ul>
<li>shell variables (how to set/get + knowledge about special ones like
PATH)</li>
<li>shell redirection (capturing output of an program)</li>
<li>pipes (extracting some information from log file is an excelent example)</li>
<li>proces... | From my experience with my numerous colleagues since I started to work, nobody wants to fake Unix knowledge: either they "<em>know their way around the command line</em>" or they simply say "no way!".
Just ask if the candidate is willing to work on a Unix workstation and let him tell you how far he can go through bash... | https://softwareengineering.stackexchange.com |
4,197,905 | [
"https://math.stackexchange.com/questions/4197905",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/947459/"
] | <blockquote>
How do I derive the Kinematics equation <span class="math-container">$v=v_0+at$</span> from the equation <span class="math-container">$x = x_0+v_0t+\frac12at^2$</span>?
</blockquote>
This is how I have tried :
<span class="math-container">$$x - x_0=v_0t+\frac12at^2$$</span>
<span class="math-container">$$\... | <strong>It is entirely possible to derive the equation without calculus, here is how:</strong>
Firstly, you are wrong in substituting <span class="math-container">$\Delta x/t$</span> with <span class="math-container">$v$</span>. The ratio <span class="math-container">$\Delta x/t$</span> is, the average velocity, and no... | Hmm how about this:
<span class="math-container">$$x(t+\Delta t)=x_0 + v_0( t + \Delta t)+ \frac12a(t+ \Delta t)^2$$</span>
We know that at each and every point the velocity is different since there is an acceleration, but let's take a small time interval <span class="math-container">$(t,t+\Delta t)$</span>, then chang... | https://math.stackexchange.com |
195,193 | [
"https://dba.stackexchange.com/questions/195193",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/142251/"
] | Using Firebird, I have two tables, <code>Orders</code> and <code>DespatchedParts</code>.
<code>Orders</code> table:
<pre><code>ID CustomerID Total_number_parts
-- ---------- ------------------
1 1 5
2 1 4
3 2 10
4 1 5
5 3 20
</code></pre>
<code>Despatch... | You want to select all customers whose orders have been completely fulfilled. So first you need to know how many parts the customer has ordered in total:
<pre><code>select customerid, sum(total_number_parts) ordered
from orders
group by customerid
</code></pre>
You also need to know how many parts have been shipped f... | Set up test data:
<pre><code>CREATE TABLE #order (id INT, customerid INT, total_number_parts INT)
INSERT INTO #order ( id ,customerid ,total_number_parts)VALUES ( 1,1,5)
INSERT INTO #order ( id ,customerid ,total_number_parts)VALUES ( 2,1,4)
INSERT INTO #order ( id ,customerid ,total_number_parts)VALUES ( 3,2,10)
I... | https://dba.stackexchange.com |
43,165 | [
"https://quant.stackexchange.com/questions/43165",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/38051/"
] | This should hopefully be an easy question to answer, but I am new to Stochastic Calculus and am gapping as to why the following is true, for a brownian motion <span class="math-container">$W_t$</span>:
<span class="math-container">$$d(\int W_t dt ) = W_t dt$$</span>
I have seen many of the relevant linked posts about... | Compare <span class="math-container">$\int_o^t W_t dt$</span> and <span class="math-container">$\int_o^{t+dt} W_t dt$</span>
The increment between the first integral and the second is equal to <span class="math-container">$W_t dt$</span> (i.e. the value of the integrand at the upper limit of integration (<span class="... | The ito lemma applies to a function <span class="math-container">$f(t,W_t)$</span>. To help you understand why you are confused i would ask: since you believe that you can apply the ito lemma, can you explictly provide the function <span class="math-container">$f$</span> you believe is applicable in this case ?
| https://quant.stackexchange.com |
2,093,840 | [
"https://math.stackexchange.com/questions/2093840",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | I'm trying to solve the pde $u_{t}= 2u_{xx}-2u_{x}+u$, $0<x<1$, if $u(0,t) = 0$, $u(1,t)=0$ and $u(x,0)=1$.
I tried the change of variables $u(x,t)= e^{x-t}v(x,t)$, but when I do so, only the linear term $u$ disappears and my b.c.'s and I.c.'s have exponential terms in the denominator.
I'm thinking this probab... | Continuing on from caverac's answer, I'm going to approach this slightly differently - I'll call the separation constant $-c^2$, which will make things easier in the long run. It's no restriction, because $c$ could be complex (it will turn out that it isn't).
So, we have two ordinary differential equations to solve.
... | Call $u(x,t) = X(x)T(t)$ and replace it in your PDE, you should arrive to
$$
\frac{1}{T(t)}\frac{{\rm d}T(t)}{{\rm d}t} = \frac{2}{X(x)}\frac{{\rm d}^2X(x)}{{\rm d}x^2} - \frac{2}{X(x)}\frac{{\rm d}X(x)}{{\rm d}x} + 1
$$
So you have a function of $x$ in one side, and a function of $t$ on the other side of the equati... | https://math.stackexchange.com |
76,351 | [
"https://physics.stackexchange.com/questions/76351",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/10896/"
] | <blockquote>
A current $I$ flows in a long thin walled cylinder(parallel to the axis) of radius $R$. What pressure do the walls experience?
</blockquote>
This is the 263<sup>rd</sup> problem in Section III from the book 'Problems In General Physics by IE Irodov'.
<hr>
<strong>My attempt:</strong>
Consider a thin ... | That is because the magnetic force acting on the infinitesimal surface is not $\mu _0 I^2/2\pi R=B$ but $0.5B$ . The factor of half is present because the field inside the cylinder is zero and outside it, is $B$ and therefore the "average value" is $B/2$ acting on the segment. Actually, a better and correct way of unde... | <img src="https://i.stack.imgur.com/65zm3.jpg" alt="enter image description here">
I have provided the solution in the image..See basically You are right till the Magnetic field part but You have to mention current in force part in terms of Current Per unit length as u have taken a strip here.. Hope this help
P.S. I... | https://physics.stackexchange.com |
186,160 | [
"https://softwareengineering.stackexchange.com/questions/186160",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/41216/"
] | Following a standard framework of project management, for a software development project we will provide deliverables (documents and software) at the end of each month :
<img src="https://i.stack.imgur.com/Bf945.png" alt="enter image description here">
My question is:
<ul>
<li>From May to June, while software is in ... | As you said changes could happen along the way, would it be possible to shorten the cycle time to just 1 - 2 weeks and not wait until the end of each month? This will give user something to see as you're developing the software and also user can give some feedback more quickly. This will make them feel that they visual... | Based on the above you have a schedule of work. That work includes the specifications, technical requirements and a prototype.
Based on this I would expect that the deliverables in May->August would be a phased release of the application/project with each release building on the prototype so that in May the applicatio... | https://softwareengineering.stackexchange.com |
404,979 | [
"https://electronics.stackexchange.com/questions/404979",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/203326/"
] | I need to create a logic gate which will find out whether a number is negative or not.
The input is 8 bits and the output is 1 bit, and if the input is 1 (i.e. negative number) then the output should also be 1, but if the input is 0, then the output should also be 0, so it kinda works like a NOT gate without the inve... | Adding the maxima (from the normal operations sections) of your ICs will yield a (very conservative) upper bound on your current consumption.
To get at a more realistic value you can either measure, or figure out how the actual values vary with the circumstances. Power voltage, temperature, operating mode, and clock ... | No, you can't just take current and voltage values from the dc characteristics table and multiply them. The problem with this approach is that a typical device cannot meet those maximum current and voltage ratings <strong>at the same time</strong>. Your calculations will be grossly incorrect.
Consider a 2N3904 transis... | https://electronics.stackexchange.com |
162,240 | [
"https://security.stackexchange.com/questions/162240",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/151266/"
] | Can a malware that infected your local computer compromise a KeePass database stored locally in any way?
If yes, what's the point for KeePass to have such strong security mechanisms if it cannot resist to this scenario? If you keep your DB locally, isn't this scenario the main threat that exists?
| When your computer is compromised, pretty much any defense on it should be considered broken. Security threat models consider this as an out-of-scope scenario - barring very few exceptions (e.g., the very purpose of your software is to be the last-line of defense).
That said, password managers (like KeePass) that sto... | Yes - if the malware included a keylogger, for example, it could simply read the master password when you typed it in. The only real way to prevent that would be to have KeePass be the only software running, on a verified secure computer (e.g. no hardware keyloggers, no VMs, etc.) which would somewhat defeat the purpos... | https://security.stackexchange.com |
626,451 | [
"https://electronics.stackexchange.com/questions/626451",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/29285/"
] | I am building a smart lock and while the software and hardware parts are OK, the electronics part are an adventure for me.
I have an old 230-12V power unit and I need to use it to power both a Raspberry Pi (5V) and the lock (12V). I found a 12→5V converter and the last part remaining is to be able to control the 12V po... | That mental model of a Zener diode is slightly too simplistic. A Zener diode isn’t a simple switch. In all operating regions it has shunt capacitance. With “small” reverse bias voltage, it is a soft voltage-controlled current source. In active state, it’s a voltage source with nonlinear internal series resistance (ESR)... | The reverse VI curve slope is related to the forward Vf vs If diode current in Zener mode.
You must not use a 1 Ohm series R for a current limiter but rather limit that to just include the load max
plus a small mA for full load to regulate.
They are only used for low power applications. Pay attention to the datasheets... | https://electronics.stackexchange.com |
403,980 | [
"https://physics.stackexchange.com/questions/403980",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/74430/"
] | When I studied electromagnetism the $\mathbf{B}$ and $\mathbf{E}$ fields were introduced as fundamental quantities to me, and the $\mathbf{H}$ and $\mathbf{D}$ fields were introduced as something of an afterthought in order to more easily work with free currents and charge densities in materials (I understand that this... | This is an interesting question that calls for a proper historical analysis, but here is one pragmatic reason.
The vectors $\mathbf E$ and $\mathbf H$ are used because they are more directly related to what is an independent variable (chosen by experimenter) when the measurement of behaviour of the medium is done by c... | Your puzzlement is appropriate. It all goes back to periodic units conferences where these issues were settled democratically, with engineers and telegraphers outnumbering physicists. H was chosen because a technician looked at a dial where the current was given as H, using~NI/L. Since H_tangential is continuous, H i... | https://physics.stackexchange.com |
153,144 | [
"https://electronics.stackexchange.com/questions/153144",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/28383/"
] | I need a contact temperature sensor to get the temperature of a container.
Anything like LM35 which I found from google search gives me ambient temperatures. Can anyone suggest an easy to use <strong>contact</strong> temperature sensor? Accuracy as high as possible! I am going to use it with an Arduino Due, if that in... | You can use the LM35 version that comes in a TO-220 and bolt it to the container, then thermally insulate the exposed side.
<img src="https://i.stack.imgur.com/1Nrbt.png" alt="enter image description here">
Note that the tab is electrically connected so you may need to add an (electrical) insulator pad.
There are ... | LM35 will do the job. The issue is not the sensor, but the way you use it. You must have good thermal contact with the element that you want to measure and isolation from the rest.
One way to do it is to insert the LM35 in a radiator (same as you would use to cool a LDO) that is soldered to the element to be measured... | https://electronics.stackexchange.com |
434,595 | [
"https://mathoverflow.net/questions/434595",
"https://mathoverflow.net",
"https://mathoverflow.net/users/136218/"
] | Given the positive integers <span class="math-container">$n$</span> and <span class="math-container">$m$</span>, consider the set of graphs <span class="math-container">$\mathcal{G} = \{G=(V,E): |V|=n \land |E|=m\}$</span>.
For which values of <span class="math-container">$n$</span> and <span class="math-container">$m$... | For <span class="math-container">$n=53$</span> and <span class="math-container">$m=113$</span>, you can't even get close in general. Take 7 copies of <span class="math-container">$K_5$</span> and 3 copies of <span class="math-container">$K_6$</span>, all disjoint. Remove any two edges; now you have 53 vertices and 113 ... | Let <span class="math-container">$\psi(n)\approx\sqrt{n}$</span> denote the positive solution to <span class="math-container">$x^2+2x=n$</span>. Note that if <span class="math-container">$|V_1||V_2|+|V_1|+|V_2|>n$</span>, then either <span class="math-container">$|V_1|\geq \psi(n)$</span> or <span class="math-contai... | https://mathoverflow.net |
35,021 | [
"https://stats.stackexchange.com/questions/35021",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/13561/"
] | I am dealing right now with a lot of distributions, e.g., $F$, $t$, $\chi^2$.
I was wondering why do these degrees of freedom signify for distributions such as the $F(m,n)$ distribution?
| Here is a less technical answer, perhaps more accessible to people with modest mathematical preparation.
The term degrees of freedom (df) is used in connection with various test statistics but its meaning varies from one statistical test to the next. Some tests do not have degrees of freedom associated with the tes... | The F distribution is the ratio of two central chi-square distribution. The m is the degrees of freedom associated with the chi-square random variable that represents the numerator and the n is the degrees of freedom of the chi-square for the denominator. To complete the answer to your question I need to explain the c... | https://stats.stackexchange.com |
4,631,957 | [
"https://math.stackexchange.com/questions/4631957",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/998543/"
] | Let <span class="math-container">$X_1,...,X_n$</span> be some random variables and <span class="math-container">$\theta$</span> be a function of these random variables. I was asked to show that <span class="math-container">$\mathbb{P}(\theta=\hat{\theta}|X_1,...,X_n)=c$</span> almost surely. I am able to calculate the ... | Given a particular realization <span class="math-container">$x_1, \ldots, x_n$</span> of <span class="math-container">$X_1\ldots, X_n$</span>, the conditional probability <span class="math-container">$P(\theta = \hat \theta|x_1\ldots, x_n)$</span> is a specific number on <span class="math-container">$[0,1]$</span>. But... | I guess that you understood wrongly what has been said to you about <span class="math-container">$\theta $</span>. If <span class="math-container">$\theta $</span> is an unknown parameter, that defines a probability distribution, and we want to estimate it using a random sample <span class="math-container">$X_1,\ldots ... | https://math.stackexchange.com |
164,190 | [
"https://math.stackexchange.com/questions/164190",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/14497/"
] | I'm trying to understand a step in a proof. I don't get a special trick that is used several times in the book I am reading, so this does not get out of my head. I try to explain the prerequisites and what I don't understand:
Let $Y$ be a Banach space and let $S$ be a set. For a mapping $f:S\to Y$ let
$\|f\| := \sup_{... | Assume we are give two sequences $\{a_r:r\in\mathbb{N}\}$ and $\{b_r:r\in\mathbb{N}\}$ such that for all $r\in\mathbb{N}$ we have $a_r\leq b_r$. Fix some $l\in\mathbb{N}$ and consider the last inequality for all $r\geq l$. After taking infimum on the left side over all $r\geq l$ we get
$$
\inf\limits_{r\geq l}a_r \leq ... | Notice that
\begin{equation}
|f_l(x) -f_k(x)| \le \|f_l - f_j\|
\end{equation}
for all $l$. Then $(f_k(x))_k$ is a Cauchy sequence and
\begin{eqnarray}
\lim_{l\rightarrow \infty} |f_l(x) -f_k(x)| &=& \liminf_{l \rightarrow \infty} |f_l(x) -f_k(x)| \\
&\le& \liminf_{l \rightarrow \infty} \|f_l - f_j\|
\e... | https://math.stackexchange.com |
5,483 | [
"https://stats.stackexchange.com/questions/5483",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/2380/"
] | Lets say for example a class of students and their grades are the data set.
Lets say there are around 35 students.
Here is what you know:
<pre><code>Your mark
The class average
The median mark
The standard deviation
</code></pre>
Are there any other conclusions about this data that can be made given this information... | Difficult to diagnose without looking at the results, but here is a wild guess: if in the fit the variance associated to the level component is large, that component will "follow" your data. The filtered estimates will nearly coincide with observations, and the forecasts will appear to lag them --which, as I understand... | So you have monthly data with trend and seasonality and you want to both analyse the trend/seasonal components and produce forecasts. These are two separate tasks. While you can do both with <code>dlm</code>, there are simpler approaches if you separate the tasks.
For studying the trend and seasonality, I suggest usin... | https://stats.stackexchange.com |
34,866 | [
"https://electronics.stackexchange.com/questions/34866",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/-1/"
] | I have a microcontroller device with battery power. Currently I toggle power by simple on/off switch. I want to toggle power by one pushbutton with minimal modification of the schematic (and microcontroller program probably) and with <em>no</em> consumption when device is off. How can I do it?
<strong>ADDED</strong>. ... | Based on the circuit you provide, you could just add a diode in series right after the switch (S1) (cathode connected to the switch) and them you could use an input to detect if the switch was pressed again, if so, turn off PB3.
<br>
<img src="https://i.stack.imgur.com/kPAWl.png" alt="Modification required">
The zener... | How off do you really need off to be? Many modern microcontrollers have sleep current well below the self-discharge current of even small batteries. You can have the pushbutton simply drive the I/O pin of the micro, which then toggles itself between sleep and active mode each button press. Some debouncing will be ne... | https://electronics.stackexchange.com |
2,070 | [
"https://security.stackexchange.com/questions/2070",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/1350/"
] | Not sure if what I'm saying makes sense... but is it possible for me to alter a $_SESSION variable from outside the target PHP script?
One of our scripts uses a $_SESSION variable and I'm not sure if that is vulnerable to manipulation from outside as a $_POST variable is...
| The answer to this depends on whether or not your application uses GET or POST data to populate SESSION data.
Say for example that the $_SESSION['username'] is populated when the user logins like this:
<pre><code>$_SESSION['username'] = $_GET['login-username']
</code></pre>
As the XSS owns your client he can also m... | The <code>$_SESSION</code> Variable is never sent to the Client. It is stored exclusively on the server. The user only gets an ID, which PHP uses to load up the corresponding <code>$_SESSION</code> variable.
So no, by exclusively using XSS, you cannot change the <code>$_SESSION</code> variable.
<h3>Clarification</h3>
I... | https://security.stackexchange.com |
608,437 | [
"https://electronics.stackexchange.com/questions/608437",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/132183/"
] | I would like to create a parametric bit-width assignment in Verilog.
Something like the following code:
<pre><code>module COUNTER
(
CLEAR,
CLK,
CODE)
#(parameter BUS_WIDTH = 8)
reg [BUS_WIDTH-1:0] CODE;
always @(posedge CLK... | You were very close. The proper syntax is as follows:
<pre><code> CODE <= {BUS_WIDTH{1'b0}};
CODEreg <= {BUS_WIDTH{1'b0}};
</code></pre>
Refer to IEEE Std 1800-2017, section 11.4.12.1 <em>Replication operator</em>.
The one bit value (<code>1'b0</code>) is replicated 8 times to form th... | There is no need to do this unless you have linting tools and need to suppress warnings about mismatched sizes. Verilog implicitly pads or truncates expressions to the appropriate width.
<pre><code>if(CLEAR)
begin
CODE <= 0;
CODEreg <= 0;
end
</code></pre... | https://electronics.stackexchange.com |
20,415 | [
"https://datascience.stackexchange.com/questions/20415",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/35584/"
] | I am trying a simple example with sklearn decision tree. I am giving "number,is_power2,is_even" as features and the class is "is_even" (of course this is stupid)
Here is the code
<pre><code>from sklearn import tree
features =[[1,0,0] , [2,1,1] , [3,0,0] , [4,1,1] , [5,0,0] , [6,0,1] , [900,0,1] , [1001,0,0]] #val,... | The names should be given in ascending numerical order.
Saw this in the code's docs:
<pre><code>class_names : list of strings, bool or None, optional (default=None)
Names of each of the target classes in ascending numerical order.
Only relevant for classification and not supported for multi-output.
If ``T... | What you need to do is convert labels from string/char to numeric value. For instance 'o' = 0 and 'e' = 1
So your labels will look like this
<pre><code>labels = [0, 1, 0, 1, 0, 1, 1, 0]
</code></pre>
class_names should match those numbers in ascending numeric order
<pre><code>0 - 'o'
1 - 'e'
class_names=['o', 'e'... | https://datascience.stackexchange.com |
1,442,739 | [
"https://math.stackexchange.com/questions/1442739",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/45400/"
] | Suppose we have a fraction
$$I=\int\frac{dy}{(1+y^2)(2+y)}$$
How is it possible that
$$5I = \int\frac{dy}{y+2}-\int\frac{ydy}{1+y^2}+\int\frac{2dy}{1+y^2} ?$$
How are they using partial fractions to do this?
| Setting
$$\frac{1}{(1+y^2)(2+y)}=\frac{A}{y+2}+\frac{By+C}{1+y^2}$$
gives
$$1=A(1+y^2)+(y+2)(By+C),$$
i.e.
$$0y^2+0y+1=(A+B)y^2+(C+2B)y+A+2C$$
Then, solve the following system :
$$0=A+B,\quad 0=C+2B,\quad 1=A+2C$$
| $$\begin{align*}
\frac1{y+2}-\frac{y}{1+y^2}+\frac2{1+y^2}&=\frac1{y+2}+\frac{2-y}{1+y^2}\\
&=\frac{(1+y^2)+(4-y^2)}{(y+2)(1+y^2)}\\
&=\frac5{(y+2)(1+y^2)}
\end{align*}$$
| https://math.stackexchange.com |
121,615 | [
"https://mathoverflow.net/questions/121615",
"https://mathoverflow.net",
"https://mathoverflow.net/users/27832/"
] | Let $n\geqslant 5$ and let $E_4(n)$ be a linear subspace of $(n\times n)$- real skew-symmetric matrices such that
$$
rank(A)=4,\text{ for all }A\in E_4(n),A\neq 0.
$$
I'm curious about the following question:
QUESTION:
What can be said about the dimension of $E_4(n)$? Of course, it is easy to check that $\operatorna... | Partial progress: It's easy to achieve $n-3$. Consider matrices of the form
$$\begin{pmatrix}
0 & 0 & r_1 & r_2 & \cdots & r_{n-3} & 0 \\
0 & 0 & 0 & r_1 & \cdots & r_{n-4} & r_{n-3} \\
r_1 & 0 & & & & & \\
r_2 & r_1 & & & & ... | Let $J_4(n)$ be the $n \times n$ matrix
$$\begin{pmatrix}
0 & 1 & 0 & 0 & 0 & 0 & \cdots \\
-1 & 0 & 0 & 0 & 0 & 0 & \cdots \\
0 & 0 & 0 & 1 & 0 & 0 & \cdots \\
0 & 0 & -1 & 0 & 0 & 0 & \cdots \\
0 & 0 & 0 & 0 ... | https://mathoverflow.net |
123,836 | [
"https://mathoverflow.net/questions/123836",
"https://mathoverflow.net",
"https://mathoverflow.net/users/32008/"
] | Let a finite group $G$ acts on an orientable manifold $X$ freely. Denote $\pi:X\rightarrow Y=X/G$ be the quotient map. This covering map defines two maps between cohomology groups $\pi^*=H^\ast(\pi):H^*(Y,\mathbb{Z})\rightarrow H^*(X,\mathbb{Z})$ and $\pi_!:H^*(X,\mathbb{Z})\rightarrow H^*(Y,\mathbb{Z})$. The latter ma... | The first identity $\pi_! \circ \pi^* = \vert G \vert \cdot \mathrm{Id}$ holds, and follows from knowing that $\pi_!$ is a $H^*(Y)$-module map via $\pi^*$, so
$$\pi_!( \pi^*(x)) = \pi_!(1)\cdot x$$
and $\pi_!(1) = \vert G \vert$ as may be seen from the $G$-cover over a point.
The second proposed identity $\pi^* \circ ... | Yes: Let $\alpha$ be a cohomology class in $Y$. For simplicity, let's assume that $PD_{Y}\alpha$ is represented by an embedded cycle in $Y$. Then $PD_{X}\pi^{*}\alpha=\pi^{-1}PD_{Y}(\alpha)$. Therefore, $\pi\circ PD_{X}\pi^{*}\alpha = \pi (\pi^{-1}PD_{Y}\alpha)=|G|PD_{Y}\alpha$ as the map $\pi: \pi^{-1} PD_{Y}\alph... | https://mathoverflow.net |
70,756 | [
"https://security.stackexchange.com/questions/70756",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/396/"
] | I'm seeing a virus in our network with some strange headers. Sometimes they are coming (sourced) from a netscaler VIP, other times they seem to come from an Exchange hub server.
How do I determine the origin of this virus? (workstation, etc)
I'm thinking that this has to do with special authentication of the receiv... | <h1>OpenSSL s_client</h1>
To check if you have disabled the SSLv3 support, then run the following
<pre><code>openssl s_client -connect example.com:443 -ssl3
</code></pre>
which should produce something like
<pre><code>3073927320:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1258:SSL... | On a side note you can use <code>nmap</code> with ssl-enum-ciphers script as follows
<pre><code>nmap --script ssl-enum-ciphers -p 443 example.com
</code></pre>
You will get a response like this.
<pre><code>PORT STATE SERVICE
443/tcp open https
| ssl-enum-ciphers:
| SSLv3:
| ciphers:
| TLS_ECDHE_RS... | https://security.stackexchange.com |
283,136 | [
"https://mathoverflow.net/questions/283136",
"https://mathoverflow.net",
"https://mathoverflow.net/users/6506/"
] | Let $K$ be a number field and let $K(a,b)$ be the field of rational functions with two indeterminates over $K$. Consider the elliptic curve $E$ over $K(a,b)$ defined by the Weierstrass equation
\begin{equation*}
E : y^2=x^3+ax+b.
\end{equation*}
What is the torsion subgroup and the rank of the Mordell-Weil group of $E$... | Specialize $a,b$ to functions giving the universal elliptic curve over the modular curve $X_0(N)$. These are known to have rank zero over the function field of the modular curve with coefficients over $\mathbb{C}$ even. They can have torsion but, by varying $N$, you can show that the torsion is trivial too.
T. Shioda... | If you want to do this directly, you could "partially specialize" to, say $y^2 = x^3 + Ax + T$ with $A\in\mathbb C$. Then I don't think it's very hard to show, via a standard descent, that as an elliptic curve over $\mathbb C(T)$, the rank is $0$, and that for most $A$, the torsion is trivial, too. Actually, for the ra... | https://mathoverflow.net |
418,967 | [
"https://stats.stackexchange.com/questions/418967",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/254597/"
] | While reading a book on statistics, I encountered the following:
<span class="math-container">$$f(x) = \mathop{\text{argmin}}\limits_c E_{Y|X}([Y-c^2]|X=x)\tag{1}$$</span>
which somehow equates to
<span class="math-container">$$f(x) = E(Y|X=x)\tag{2}$$</span>
How do we get from result <span class="math-container">$(1)... | Simply differentiate <span class="math-container">$f$</span> with respect to <span class="math-container">$c$</span> (your square operation must be outside the differencing):
<span class="math-container">$$\begin{align}\frac{\partial f}{\partial c}&=\frac{\partial}{\partial c}\left(E[(Y-c)^2|X=x]\right)\\&=\fra... | The answer follows exactly the same path than non conditional probability.
Say your proba <span class="math-container">$\mathbb{P}(.|X=x)$</span> is just a another proba <span class="math-container">$\mathbb{Q}$</span>, then you know
<span class="math-container">$argmin_c \mathbb{E}_{\mathbb{Q}}[Y-c]^2$</span> is <sp... | https://stats.stackexchange.com |
4,037,234 | [
"https://math.stackexchange.com/questions/4037234",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/813572/"
] | From Chapter 1, page 9 of Spivak's <em>Calculus</em>, 3rd edition:
<blockquote>
In fact, it is convenient to consider the collection of all positive numbers, denoted by <span class="math-container">$P$</span>, as the basic concept, and state all properties in terms of <span class="math-container">$P$</span>:
(P10) (Tri... | I had the same thought about this problem. It's easy to be confused about which properties still hold.
The key point is that here, we aren't allowed to use the equivalence of <span class="math-container">$a<0$</span> and <span class="math-container">$-a>0$</span>. This equivalence is actually what Spivak's provin... | Because then what we would have would be:
<blockquote>
For any number <span class="math-container">$a$</span>, one, and only one, of the following holds: (i) <span class="math-container">$a=0$</span>, (ii) <span class="math-container">$a<0$</span>, (iii) <span class="math-container">$0<a$</span>.
</blockquote>
It... | https://math.stackexchange.com |
223,268 | [
"https://softwareengineering.stackexchange.com/questions/223268",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/62298/"
] | Given the class:
<pre><code>public class Foo : IFoo
{
private IBarRepository repository
public Foo(IBarRepository repository)
{
this.repository = repository
}
public IList<IBar> Bars { get; private set; }
}
</code></pre>
My long standing instinct is to initialise the list of IBar in the constru... | Well, the simple answer to your question is
<pre><code>public readonly IList<IBar> Bars = new List<IBar>();
</code></pre>
But I think you should question your premise.
<blockquote>
but using Constructor Injection, the Single Responsibility of the constructor is for it to set the dependancies for the cl... | The Single Responsibility principle applies to the class as a whole, not just to the constructor. Also, resist the urge to initialize the Bars variable using that last method - if you are using injection, it should be responsible for giving you a complete and working instance of Foo or none at all if it can't resolve t... | https://softwareengineering.stackexchange.com |
230,747 | [
"https://mathoverflow.net/questions/230747",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1840/"
] | A set of $d \times d$ real or complex matrices is commonly called <em>irreducible</em> if those matrices do not jointly preserve a linear subspace with dimension strictly between zero and $d$. A stronger hypothesis which is useful in multiplicative ergodic theory - for example, in Furstenberg's theorem on random matrix... | The answer to your second question is <strong>no</strong>.
Let $E_1$, $E_2$, $E_3$ be pairwise transverse $2$-dimensional subspaces of $\mathbb{R}^4$.
Consider the following semigroup:
$$
\Sigma := \{M \in \mathrm{Mat}(4,4) ; \; M(E_i)=E_i, i=1,2,3\}.
$$
<strong>[Edit]</strong> The following remark will be useful: An... | In case your set consists of non-singular (=invertible) matrices, the condition of strong irreducibility is equivalent to the condition that the connected component of identity of the Zariski closure of the group generated by your set acts irreducibly on ${\mathbb C}^d$. In both your cases, this is satisfied.
Suppose... | https://mathoverflow.net |
3,097,393 | [
"https://math.stackexchange.com/questions/3097393",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/167818/"
] | Let <span class="math-container">$H$</span> be a Hilbert space with induced norm <span class="math-container">$|\cdot|$</span>, with <span class="math-container">$C\subset H$</span> a closed, convex subset of <span class="math-container">$H$</span> and <span class="math-container">$P_C(x)$</span> the projection of <spa... | Split <span class="math-container">$x-y$</span> into the path from <span class="math-container">$x$</span> through <span class="math-container">$P_C(x)$</span> and then in the orthogonal direction after some while. Then use Pythagoras. Let me know if you need details, but try just sketching this down on a piece of pape... | First <span class="math-container">$z = P_C(x)$</span> if and only if
<span class="math-container">$$
\langle z - x, y-z\rangle \ge0 \quad \forall y\in C.
$$</span>
This follows from
<span class="math-container">$$
\frac12|y-x|^2 - \frac12|z-x|^2 = \langle z-x, y-z\rangle + \frac12 |y-z|^2.
$$</span>
Now take <span cla... | https://math.stackexchange.com |
486,193 | [
"https://physics.stackexchange.com/questions/486193",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/199873/"
] | This question pertains specifically to the case of a constant pure 4-force in special relativity, of the form <span class="math-container">$\textbf{F} = (f_0, f_x, 0, 0)$</span>, where <span class="math-container">$f_0 = \frac{γ}c \frac{dE}{dt}$</span>. I understand how to solve the case of a constant 3-force in specia... | The confusion here is that many very able physicists have picked up the idea that motion at constant proper acceleration is somehow motion at "constant 4-acceleration" and thus "constant 4-force", but this is simply not true.
For rectilinear motion at constant proper acceleration <span class="math-container">$a_0 = A... | The four-force is the rate of change of four-momentum in respect to the proper time, that is <span class="math-container">$$ {\bf F} = \frac{d{\rm P}}{d\tau}$$</span>
If it was constant that means that <span class="math-container">$$ {\bf P}(\tau) = {\bf P}_0 + {\bf F}\tau$$</span>
However that would mean that the mass... | https://physics.stackexchange.com |
12,687 | [
"https://quant.stackexchange.com/questions/12687",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/6782/"
] | I am trying to teach myself about interest rate swaps, how they are priced, etc... Easy enough - just comparing cash flows of fixed and floating rate bonds.
However, what I'm struggling with is how the future interest rates (as well as the discount factors) are being determined. These are never clearly explained and t... | There are two parts to your question and I'd like to answer them separately.
<h1>Curve Construction</h1>
On a daily basis, you can observe prices on a large variety of instruments, whose prices are driven by news and trading flows. Based on market prices of these instruments, there are a number of ways to create disc... | I don't think they are implying that future interest rates are predictable. They may be speaking of implied forward rates as predictors of future rates or, generally, of the yield curve as an expectation of the future path of short-term interest rates.
If $P(0,T_1)=1/(1+r_1)$ and $P(0,T_2)=1/(1+r_2)$ are the prices to... | https://quant.stackexchange.com |
63,826 | [
"https://mathoverflow.net/questions/63826",
"https://mathoverflow.net",
"https://mathoverflow.net/users/14865/"
] | I am currently stuck at a problem which seems too easy to be stuck at to me...
<h3>Summary</h3>
Let $H$ be the convex hull of the points $d_1,\ldots, d_n\in \mathbb{R}^d$. How can one compute
\[\min_{x\in H}||x||^2_2 \]
efficiently?
<h3>Conditions one should know about</h3>
When I talk about efficiency in this que... | Dear all,
I think I found quite a neat solution for my problem. At first I want to give humble thanks to Roland, who greatly inspired the solution I'm going to use now. Just in case somebody else might sometimes in the future be struggling with a similar problem, I'm going to give a short outline of the ideas and a ro... | The following iterative algorithm is perhaps fast:
Set $P=d_i$ where $d_i$ is of minimal norm among $d_1,\dots,d_n$.
Iterate the following loop:
Let $j=j(P)$ be an index such that $\alpha=\langle P,d_i-P\rangle/\sqrt{\langle d_i-P,d_i-P\rangle}, i=1,..n$ is minimal for $i=j$.
If $\alpha\geq 0$ then $P$ is at minima... | https://mathoverflow.net |
170,947 | [
"https://security.stackexchange.com/questions/170947",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/133325/"
] | I'm investigating behavior of SSL decryptors on OpenVPN connections to port 443 and I noticed that device I use as decryption proxy doesn't recognize OpenVPN connections as TLS thus doesn't decrypt them. The question is then - how does OpenVPN protocol differ from standard TLS?
| Openvpn uses TLS for authentication and key exchange but it does not use it for the actual data encyption. When running on UDP openvpn runs the TLS session on top of a custom "reliability layer", i'm not sure what it does when running on TCP.
Furthermore an openVPN network uses it's own CA to authenticate both server ... | OpenVPN provides different ways to management VPNs on your device. OpenVPN uses OpenSSL (a TLS implementation) to provide TLS tunneling. It simply uses the TLS protocol to establish a secure tunnel.
OpenVPN uses its own protocol to authenticate with an OpenVPN server, and manage connections. However, the actual t... | https://security.stackexchange.com |
2,122,990 | [
"https://math.stackexchange.com/questions/2122990",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/235537/"
] | I am representing a set of images with a matrix $x$ that is of shape $(k, n)$. I want to treat all images $x^*:= AxB$, where $A$ is an invertible matrix of shape $(k,k)$ and $B$ is an invertible matrix of shape $(n,n)$, as being equivalent to $x$. Both $A$ and $B$ are known. i.e., a practically relevant distance metric... | It is more practical to perform a preliminary manipulation to simplify the integrand function.<br> Since $\sin(\pi+\theta)=-\sin(\theta)$, $\sin(\theta)=\sin(\pi-\theta)$, $\sin(\pi/2-\theta)=\cos(\theta)$ and $\cos^2(\arctan t)=\frac{1}{1+t^2}$,
$$\begin{eqnarray*} I(\alpha)&=&\int_{0}^{2\pi}\frac{d\theta}{1+... | Using contour integration ...
\begin{eqnarray*}
\oint \frac{2dz}{2iz+(z^2-1)\cos(\alpha)}
\end{eqnarray*}
where the contour of the integral is the unit circle (as stated in the question ?). Rearrange to
\begin{eqnarray*}
\frac{2}{\cos(\alpha)} \oint \frac{dz}{\left( z+i\frac{1+\mid\sin(\alpha)\mid}{\cos(\alpha)} \righ... | https://math.stackexchange.com |
502,778 | [
"https://electronics.stackexchange.com/questions/502778",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/25862/"
] | I often find that consumer electronics from reputable brands come with fused plugs that are rated significantly higher than the actual product.
I would have thought that the <em>ideal</em> fuse would be <span class="math-container">\$x+\epsilon\$</span> where <span class="math-container">\$x\$</span> is the product's ... | The purpose of the fuse is not to protect the product, it's to protect the wiring — to keep it from getting hot enough to start a fire. The fuse is rated according to the gauge of the wire. The only connection with the actual power consumption of the product is that the wire gauge must be selected to support the ... | In addition to the answer by Dave Tweed, while BS1362 fuses can be bought in a wide variety of ratings, there are only two "standard" values that people are expected to keep to hand. These are 3A and 13A. 3A is for small flexes on things such as table lamps. 13A is for everything else. So long as the fuse blows bef... | https://electronics.stackexchange.com |
62,185 | [
"https://security.stackexchange.com/questions/62185",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/21051/"
] | The other day I tried to withdraw some cash from an ATM in a hurry and punched in a wrong pin. I realized that only when I hit the "ok" button, but to my surprise the ATM did not complain. It showed the usual menu, asking me to select an operation. It's only when I selected withdrawal I was prompted that the pin is inc... | This answer applies when the ATM uses the card's magnetic stripe, not when the card's chip is used.
The keyboard of an ATM is a completely separated device with special hardware security features (like self-destroying chips if someone tries to open it, etc.) because it's the bottleneck of the whole ATM security.
When... | Confirming the PIN when the card's magnetic stripe is used requires contacting the bank's server. Since this takes time (and took even more time back in the days of dialup), the ATM combines "verify the PIN" and "withdraw money" into a single contact.
The behavior might be different if the card has a chip and the ATM... | https://security.stackexchange.com |
4,500,396 | [
"https://math.stackexchange.com/questions/4500396",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1074195/"
] | I am pretty sure that, for the iterates of the backward Euler's method for <span class="math-container">$y'=f(t,y)$</span> one cannot obtain <span class="math-container">$\displaystyle \frac{y_n-y_{n-1}}{\delta t}\rightarrow y'(t^*)$</span>, for a suitable choice of <span class="math-container">$n$</span>. The reason i... | The situation is indeed somewhat complicated as you have two convergences to consider, the convergence of the difference quotient and the convergence of the numerical solutions as <span class="math-container">$δt\to 0$</span>. It should be without doubt that
<span class="math-container">$$
\frac{y(t_n)-y(t_{n-1})}{t_n-... | Not really sure what you are asking, but concerning
<blockquote>
Do you have a counterexample, and possibly a descriptions of the class of functions on which backward Euler is of higher order than 1?
</blockquote>
you can examine the Taylor expansion of
<span class="math-container">$$ \frac{y_n - y_{n-1}}{\Delta t} $$... | https://math.stackexchange.com |
350,512 | [
"https://softwareengineering.stackexchange.com/questions/350512",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/267519/"
] | I looked at using python for the AI in a security application for hobby-business but apparently you either release it as source code or it can be easily decompiled. Of the new machine learning languages/packages, which can be kept confidential?
Likely I would use it to identify between good and bad traffic and conten... | You can use architectural design to make sure your code remains confidential. If possible, you could create a web service that holds the AI logic. You would then write a client to ask your web service if the given traffic is good or bad etc. This way your algorithm is never on the clients computer. You can add authenti... | <blockquote>
Of <strike>the new machine learning</strike> languages/packages, which can be kept confidential?
</blockquote>
<h2>None. All.</h2>
Which language you use is irrelevant. If someone has control over the hardware your software is running on, they can convert it from whatever format it's in into a more readabl... | https://softwareengineering.stackexchange.com |
684,077 | [
"https://physics.stackexchange.com/questions/684077",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/305999/"
] | The <em>net</em> electric field at any point <em>inside</em> a conductor which is not connected to an EMF source is zero and an external field is present. What is <em>net</em> electric field? It is the net field due to all the charges in the universe. Now consider an electron (or for that matter a proton in the nucleus... | The electric field inside a conductor is zero.
Let's consider the alternative. If there were a field at some point in the conductor that means there would be a force on the electrons there - and they would move. They would redistribute themselves until the field became zero.
The books are talking about a scale bigger... | Physically, they will continue to move, until there is no field.
Mathematically,
For a conductor following ohms law:
<span class="math-container">$J=\sigma E$</span>
Taking the divergence of both sides
<span class="math-container">$\nabla \cdot \vec{J} = \sigma \nabla \cdot E$</span>
Sub in gauss law
<span class="math... | https://physics.stackexchange.com |
75,968 | [
"https://softwareengineering.stackexchange.com/questions/75968",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/19166/"
] | I'm writing a small application that will reset the entire “environment” consisting of various machines and applications.
Machine names are added via config file - this is read, the appropriate services are stopped and log files deleted. My problem isn’t how to do this (its already working) a bit more elegantly, bu... | <strong>Break it down</strong>
Super High level:
<pre><code>Obj-->-->--->
C -> P -> A |
^-------
</code></pre>
<ul>
<li>Configuration File/Data is read in (C)</li>
<li>Data is processed & actions taken (P)</li>
<li>Results of actions are analysed (A)</li>
<li>Feedback to Process section if ... | What you're doing sounds pretty simple, and it works. 5 classes sounds enough, the danger if you start splitting into fancy patterns is that it becomes harder to read. I'd suggest finishing up and moving on to something else.
| https://softwareengineering.stackexchange.com |
7,539 | [
"https://mathoverflow.net/questions/7539",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2623/"
] | I understand the ordinary Springer correspondence gives a bijection between orbits in the nilpotent cone for the adjoint representation and irreducible representations of the Weyl group, through action of the Weyl group on the top intersection cohomology. (I'm still learning about this, I know a very vague picture).
M... | Let me make another guess as to what you are seeing:
The Lie/algebraic group acts on the coordinate ring for the closure of the nilpotent orbit (since it acts on the nilpotent orbit). Take the weight 0 weight space of this coordinate ring; the Weyl group (realized as N(T)/T) acts on it since T acts trivially on this ... | A couple of things: Springer theory does not give a bijection between orbits of the nilpotent cone and irreducible representations of the Weyl group outside of type A: in general, there is an injective map from the irreducible representations of the Weyl group to the set of equivariant irreducible local systems on nilp... | https://mathoverflow.net |
569,061 | [
"https://physics.stackexchange.com/questions/569061",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/235742/"
] | The proton radius puzzle appears to one of the more widely known unsolved problems in physics, but doesn't it point to a much deeper issue? Nearly all of a baryon's observed mass can be attributed to the (kinetic) energy of the quarks they are comprised of. It is my understanding that their radius is also a consequence... | <blockquote>
[...] he only logical explanation would be that all three quarks are point particles at the exact same point in space.
</blockquote>
Classically, the electric dipole of three point charges <span class="math-container">$+2q, -q,$</span> and <span class="math-container">$-q$</span> at respective locations <s... | The neutron does have a nonzero <em>magnetic dipole moment</em> which was detected almost 100 years ago and taken as direct evidence for it possessing internal structure, which was much later identified as consisting of quarks in communication via gluon exchange.
The deep inelastic scattering experiments that revealed ... | https://physics.stackexchange.com |
706,204 | [
"https://math.stackexchange.com/questions/706204",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/123134/"
] | I am studying linear algebra and I have been having trouble with fully understanding the concept of vector. The definition from <code>wordnik</code> says
<code>A quantity, such as velocity, completely specified by a magnitude and a direction.</code>
As I understand, any quantity is a vector or actually CAN be descri... | Simple: multiplication between vectors is not defined, but multiplication between scalars is. If you consider scalars to be a 1-D vector, then you have a weird situation where $\mathbf{a}\mathbf{x}$ is defined only if $\mathbf{a}\in \mathbb{R}^1$, but never when $\mathbf{a}\in \mathbb{R}^n$ for $n > 1$.
Arguably, y... | I was kind of with you up until $A = 5*\mathbf{i} + 0*\mathbf{j} + ...$ because there you've implicitly used more than one scalar (you're assigning 0 to all other directions). Only in 1D will you have a vector that can be represented by precisely one scalar value, because it is enough to give both magnitude and direct... | https://math.stackexchange.com |
171,591 | [
"https://softwareengineering.stackexchange.com/questions/171591",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/70138/"
] | First off, sorry if this is answered somewhere else. I did a brief search, but wasn't sure how to ask in search terms.
I'm looking at some code and came across lot's of statements like this:
<pre><code>if ( ($a != empty_or_null_or_notDefined && $a == 5 )
</code></pre>
Is this the same as just saying:
<pre>... | At a purely logical level, presuming <code>&</code> is the local and operator, then <code>$a</code> being <code>5</code> precludes it from being <code>null</code>.
That said, in some languages, and short circuits (that is, if one operand fails, it does not check the others, as the whole clause is known to fail whe... | This code is necessary to avoid errors. If you try to access an undefined object, you get a fatal error.
Checking whether this object is not undefined before checking the value allows you to work around this error.
If the first check doesn't pass (is it undefined?), it won't check the value, thus will not throw an er... | https://softwareengineering.stackexchange.com |
30,861 | [
"https://stats.stackexchange.com/questions/30861",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/4054/"
] | I have fit a simple binary logistic GAM model in R and have used the <code>plot()</code> function to plot the results of this model. The plotted graph shows a fitted line and a confidence interval, but the scale is clearly not 0-1. Does anyone know what is being plotted? Ideally, I would like to get a graph of the pred... | The individual plots are on the scale of the linear predictor, i.e. a scale that is <code>-Inf</code> to <code>+Inf</code>. The inverse of the link function is used to map from this scale to the <code>0, ..., 1</code> scale of the response. Further note that each smooth is subject to centring constraints and so is cent... | What is being plotted is the log-odds. It's log(p/(1-p)). That's the space of the logistic regression. You can convert the values using the logistic distribution and the qlogis and plogis functions.
I don't know what GAM functions you're using but often times there are options to get the p-values out.
| https://stats.stackexchange.com |
705,303 | [
"https://physics.stackexchange.com/questions/705303",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/332707/"
] | An exercise made me consider the following Lagrangian
<span class="math-container">$$L = \dot{x}_1^2+\dot{x}_2^2+2 \dot{x}_1 \dot{x}_2 + x_1^2+x_2^2.\tag{1}$$</span>
If I didn't make a mistake the equations of motion should be given by:
<span class="math-container">$$2x_1 = 2 \ddot{x}_1 + 2 \ddot{x}_2\tag{2}$$</span>
<... | with
<span class="math-container">$$L = \dot{x}_1^2+\dot{x_2}^2+2 \dot{x_1} \dot{x_2} + x_1^2+x_2^2$$</span>
you can obtain the "mass matrix"
<span class="math-container">$$M= \left[ \begin {array}{cc} {\frac {\partial ^{2}}{\partial {{\dot{x}}_{
{1}}}^{2}}}L \left( {\dot{x}}_{{1}},{\dot{x}}_{{2}} \right) &am... | First, for dimensional reasons, let's introduce a parameter <span class="math-container">$\omega$</span> with dimensions of frequency and rewrite your original Lagrangian as
<span class="math-container">\begin{equation}
L = \dot{x}_1^2 + \dot{x}_2^2 + 2 \dot{x}_1 \dot{x}_2 + 2 \omega^2 x_1^2 + 2\omega^2 x_2^2
\end{equa... | https://physics.stackexchange.com |
46,997 | [
"https://chemistry.stackexchange.com/questions/46997",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/24150/"
] | A question in my book was as following:
<blockquote>
Benzine and chloroform are considered very toxic organic solvents that dissolve in each other and in a solution of benzine and chloroform there is 0.45 mol of benzine. Find the the percent of mass( percent concentration solutions) in this solution.
</blockquote>
... | Sorry, but the accepted answer is wrong. The problem is indeterminate. Is there 1 liter of solution, or 5 liters, or 10 liters, or some other amount?
If the problem was to be solved using mole fraction, then the problem should have been written that way. e.g.:
<blockquote>
<em>Benzine and chloroform are considered... | This is the general assumption we take when we are short of information. We obviously couldn't solve the question without knowing the number of moles in the solution. There is no answer to "why specifically 1", it is generally assumed to be so. You are going to come across a lot of questions when you would require the ... | https://chemistry.stackexchange.com |
99,015 | [
"https://chemistry.stackexchange.com/questions/99015",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/48804/"
] | Is there any way to prove that ionic compounds, for instance $\ce{NaCl}$, completely dissociate into singular $\ce{Na+}$ and $\ce{Cl-}$ ions within water by hard experimental evidence?
Besides adhering to the perfect solvation model in theory, I am interested in definitive proof of monoatomic solvation in practice.
H... | One method is by making electrical conductivity measurements on aqueous solutions of salts. If we take four strong electrolytes:
<ul>
<li>Sodium chloride</li>
<li>Potassium chloride</li>
<li>Sodium perchlorate</li>
<li>Potassium perchlorate</li>
</ul>
We can measure the electrical conductivities at very low concentra... | Taking aside modern methods on nanochemistry, many experiences can be used. The mixture will have very different properties depending on which is the final particle size, from entropy changes to conductivity changes.
You can argue in terms of conductivity just by the verification of the law of independent ionic molar ... | https://chemistry.stackexchange.com |
240,236 | [
"https://electronics.stackexchange.com/questions/240236",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/113214/"
] | I have a power bank which is rated to store 20000mAh of charge and 72Wh of energy. It is recommended by the manufacturer to charge it with a Quick Charge charger which provides 1.5 Amps with 12 Volts. The company claims that using this charger, the battery can be fully charged within 7 hours.
Now, here's what I don't... | You forgot to include the <strong>difference between the charger voltage and the battery voltage</strong> !
From 72 Wh and 20 Ah I conclude that the battery voltage is 3.6 V, that is the voltage of LiIon battery when its considered empty. When it still has charge it can be up to 4.2 V. I use an average of 4V.
The 12 ... | Your battery is 20A·h and 72W·h, meaning its rated voltage is 3.7V. As such, you cannot charge a battery like this with 12V directly. There is a converter somewhere (either in the charger, or in the battery circuitry), which steps down 12V 1.5A to a lower voltage and higher current.
| https://electronics.stackexchange.com |
10,712 | [
"https://stats.stackexchange.com/questions/10712",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/3541/"
] | I'm just reading the book "R in a Nutshell".
And it seems as if I skipped the part where the "." as in "sample.formula" was explained.
<pre><code>> sample.formula <- as.formula(y~x1+x2)
</code></pre>
Is sample an object with a field formula as in other languages? And if so, how can I find out, what other field... | The dot can be used as in normal name. It has however additional special interpretation. Suppose we have an object with specific class:
<pre><code> a <- list(b=1)
class(a) <- "myclass"
</code></pre>
Now declare <code>myfunction</code> as standard generic in the following way:
<pre><code> myfunction <- func... | Look at the help page for <code>?formula</code> with regard to <code>.</code> Here's the relevant bits:
<blockquote>
There are two special interpretations of . in a formula. The usual one
is in the context of a data argument of model fitting functions and
means ‘all columns not otherwise in the formula’: see ter... | https://stats.stackexchange.com |
48,642 | [
"https://mathoverflow.net/questions/48642",
"https://mathoverflow.net",
"https://mathoverflow.net/users/11264/"
] | Does anyone know how to parametrize the boundary of the Mandelbrot set? I am not a fractal-geometer or a dynamical systems person. I just have some idle curiosity about this question.
The Mandelbrot set is customarily defined as the set $M$ of all points $c\in\mathbb{C}$ such that the iterates of the function $z\map... | Lasse's answer expanded: Let $\psi$ be the map of the exterior of the unit disk onto the exterior of the Mandelbrot set, with Laurent series
$$
\psi(w) = w + \sum_{n=0}^\infty b_n w^{-n} =
w - \frac{1}{2} + \frac{1}{8} w^{-1} - \frac{1}{4} w^{-2} +
\frac{15}{128} w^{-3} + 0 w^{-4} -\frac{47}{1024} w^{-5} + \dots
$$
Th... | I am not quite sure what you are asking. The boundary of the Mandelbrot set certainly is not an analytic curve. In fact, a famous result of Shishikura shows that the boundary of the Mandelbrot set has Hausdorff dimension 2.
Indeed, it is not even known whether the boundary is a curve at all (i.e., locally connected): ... | https://mathoverflow.net |
14,027 | [
"https://physics.stackexchange.com/questions/14027",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5046/"
] | it would be great if someone could help me understand the following quote regarding wavefunctions :)
<blockquote>
"$$\psi(x)=\sum_n C_nu_n(x)+\int dE C(E)u_E(x)$$ The expression is schematic because we have not specified exactly which form of the continuum eigenfunctions we are supposed to use."
</blockquote>
Why i... | I think this has to do with the integration measure $dE$ which is the only thing that makes the continuum part of the expansion possibly more "schematic" than the discrete one. In general you expand your wave function in a basis of common eigenstates of a (complete) set of commuting operators, which means that every ei... | Some eigenstates may be degenerate so it is not always the energy that is a "summation subscript". In such cases there must be degeneracy factor introduced in the integrand, like $d^3p=4 \pi p^2dp \propto \sqrt{E}dE$ .
| https://physics.stackexchange.com |
45,236 | [
"https://stats.stackexchange.com/questions/45236",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/16557/"
] | They seem so similar. Are they the same thing but just referred to as different names?
| When I see panel data, I think longitudinal data, so observations collected on the same individuals at multiple times, on the same topics. Repeated cross sections should be the same topics, but you get different samples of individuals at each observation. I'd welcome other descriptions.
| The answer here is pretty straight forward:
Both pooled cross sectional data and pure panel data collect data over time (this can range from 2 time periods to any large number). The key difference between the two is the "units" we follow. I am defining units as households, countries, or whatever we are collecting data ... | https://stats.stackexchange.com |
312,443 | [
"https://physics.stackexchange.com/questions/312443",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/145509/"
] | Can somebody tell me how the units work out in Heisenberg's principle equation?
Mass in $kg$ and velocity in $m/s$ cancel partially with Planck's constant, so what kind of unit is given to $Δx$ to balance the units?
| I agree with Greg Petersen: the normalization factor should be the number of terms in the sum, i.e. $t_{\rm max}-t+1$ and not $t_{\rm max}-t$ if your sum goes from $t=0$ to $t_{\rm max}$.
Your choice of a system where each spin in the lattice had spin 1 for every $t$ is pathological: the spins are infinitely correlate... | Your sum needs to go from $1$ to $2000$ instead of $0$ to $2000$. Essentially you are taking an average so it doesn't make sense to divide by fewer values than you are summing together (i.e. $2001/2000$). If you make this correction, all your calculations above work out to $0$. This leads to an indeterminate auto-co... | https://physics.stackexchange.com |
64,762 | [
"https://dsp.stackexchange.com/questions/64762",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/48283/"
] | What are my options for Open Sourced Image Processing functionality on a Raspberry Pi?
So, I am referring to the old-school processing, using operators like open/close/erosion/dilation/threshold/convolution etc.
I am not looking for neural network based processing.
Bonus points if it has a Python interface, but C wi... | A sinusoid with a frequency that is between bins in the FFT frequency domain is circularly discontinuous in the time domain. So you can't use the same IFFT results back-to-back without the noise from this discontinuity between each IFFT window, as the end of one window will have a value too far from the beginning of t... | If this is about using the STFT, then it's about frames of audio (or whatever signal class) and, if it's about frames, it's about windows. Usually the windows we want are complementary, they add to 1. An example would be a Hann window.
So now imagine your sinusoid of an arbitrary frequency (mid bin or between bins o... | https://dsp.stackexchange.com |
362,735 | [
"https://softwareengineering.stackexchange.com/questions/362735",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/291474/"
] | Is it a good practice to use #ifdef during development to switch between different types of behavior?
For example, I want to change the behavior of existing code, I have several ideas how to change the behavior and it's necessary to switch between different implementations to test and compare different approaches. Usua... | I would prefer using version control branches for this use case. That allows you to diff between the implementations, maintain a separate history for each, and when you have made your decision and need to remove one of the versions, you just discard that branch instead of going through an error-prone edit.
| <strong>Temporarily</strong> there is nothing wrong with what you're doing (say, before check-in): it's a great way to test different combinations of techniques, or to ignore a section of code (though that speaks of problems in and of itself).
<strong>But</strong> a word of warning: <strong>do not keep #ifdef branches... | https://softwareengineering.stackexchange.com |
81,833 | [
"https://mechanics.stackexchange.com/questions/81833",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/59792/"
] | Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is.
I have a battery charger that I am thinking of using but it's currently inconvenient to do.
My question is: If I just jump start the car and run it for long enough to charge the battery, is this the same as charging th... | <blockquote>
Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is.
</blockquote>
Why is it empty?
Is it empty because the battery is old and dying and won't hold capacity?
Or is it empty because you yesterday forgot the lights on?
The correct course of action depends on t... | If the battery is completely flat, then it will have been severely degraded in capacity. Lead acid batteries don’t hold their full charge after going completely flat, so it would be best to replace the battery and make sure this doesn’t happen again.
However if you want to try to charge it, it will be less stressful f... | https://mechanics.stackexchange.com |
584,707 | [
"https://physics.stackexchange.com/questions/584707",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/208473/"
] | I realize this might be a silly question but it is plainly true that, for example, a lighthouse beacon or any powerful light source, produces a much larger "spot" the farther it falls from the origin. So why don't distant objects also look bigger than closer objects, just the opposite as in experience things ... | Your interpretation is correct.
<h2>Single Bubble Case</h2>
We have a bubble of vapour surrounded by fluid water, with the vapour having a much lower density than the water. The average gas pressure in the bubble will be equal to the average water pressure around the bubble. But the water pressure changes with the heig... | Close. When water is heated, the water which is closest to the flame will start to vibrate rapidly such that the hydrogen bonds between the water molecules will break forming a gaseous vapour. These vapours will form bubbles. Because the density of these bubbles are much lower than the surrounding water, they will feel... | https://physics.stackexchange.com |
45,503 | [
"https://electronics.stackexchange.com/questions/45503",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/15312/"
] | Let say I have a AC to DC adapter with output 19V 7.9A connected to a 150W DC to DC power supply board (PC/104) with input 14-30V and output 5V.
What is amount of current I'll get from the 5V output board? Is it 150W/5V = 30A or 7.9A?
Sorry if this is so primitive question but I can't find corresponding reference.
| It'll probably be more on the order of 135W out, or 27A @ 5V, since the first supply is only capable of 150W, and the DC-to-DC converter's efficiency is going to be on the order of 90%.
| The AC/DC and DC/DC will only draw what current they need.
Take the current for the PC/104 board, call it x.
x × 5 V is its power.
Divide by 90% (as Dave Tweed said) to get input power to the input power to the DC/DC.
| https://electronics.stackexchange.com |
547,793 | [
"https://physics.stackexchange.com/questions/547793",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/262561/"
] | Let us assume that a gravitational field is created by a mass <span class="math-container">$M$</span>. An agent is bringing a unit mass from <span class="math-container">$\infty$</span> to distance <span class="math-container">$r < \infty$</span>, both measured from mass <span class="math-container">$M$</span>.
The... | <blockquote>
The agent is always forcing the unit mass with a continuously changing Force, <span class="math-container">$\vec{F}$</span>(x) ... = <span class="math-container">$\frac{GM}{x^2}\hat{x}$</span>
</blockquote>
By your force definition, the agent is not the attractive gravitational force but is something wh... | You made a mathematical error in trying to prove the result. It arises in many scenarios.
To give you an insight into your mistake I would like to tell you the correct method of integration in physics.
Remember that we always consider an element <span class="math-container">$dx$</span> at a distance <span class="m... | https://physics.stackexchange.com |
129,414 | [
"https://physics.stackexchange.com/questions/129414",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5473/"
] | we know that for a one component system
$$U= TS - PV + N \mu$$
Now all terms on the right hand side have well defined zeros, but the internal energy is known to be a relative quantity, with no unique zero. What's going on?
Similarly, we derive the above from the fact that:
$$U(kS, kV, kN)= kU(S,V,N)$$
And it seems... | The statement <em>"the internal energy is known to be a relative quantity, with no unique zero"</em> refers probably to the fact that for common systems of thermodynamics that <em>do not lose or gain matter</em>, the First law of thermodynamics implies the internal energy is a function of temperature $T$ and volume $V$... | I think in your arguments you're neglecting the potential energy from intermolecular forces, or should I say the chemical bonding energy of your system or even mass-energy of the atoms. Meaning that even if you consider the 0 Kelvin case and freeze all degrees of freedom (vibrational, transnational, rotational) you sti... | https://physics.stackexchange.com |
48,014 | [
"https://engineering.stackexchange.com/questions/48014",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/24766/"
] | I am a software engineer and have hobbyist understanding about electronics, so this is something completely out of my scope. Just need to understand if my idea of thermal storage is practical at all.
So, I have a basement in my apartment building and I have renovated and insulated it. But of course it is not heated. Wi... | That is true. A point within a body which is acted upon by force(s), and if you make an element at different rotations/orientations at the same point, then you will get different values of stresses. A Mohr's circle is used to observe the limits of the stresses for a 2D as well as 3D element case. To draw a Mohr circle,... | Yes there is an infinite number of normal and shear stress combinations, one for each different rotation angle.
However, there is a relationship between the magnitudes of the normal and shear stress at all different orientations.
| https://engineering.stackexchange.com |
415,329 | [
"https://stats.stackexchange.com/questions/415329",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/252317/"
] | In calculating sensitivity rates where TP =0 and FN =0 and the formula is TP/(TP+FN) - although it mathematically won't compute, does this equate to 100% sensitivity since it has correctly identified no true-positives?
| You can look at this as binomial proportions. I.e. proportion of correctly identified cases out of the ones that should be identified.
So you could use all the theory for estimates (and confidence intervals) for sparse binomial data. One reasonable approach could be to assume a Beta(1/3, 1/3) (or a Beta(1/2, 1/2) or ... | <span class="math-container">$TP$</span> and <span class="math-container">$FN$</span> are discrete variables. Let's pretend as if they're continuous, and investigate the limiting case using well-known techniques in multivariable calculus. For simpler notation, let <span class="math-container">$x=TP, y=FN$</span>; and w... | https://stats.stackexchange.com |
272,198 | [
"https://mathoverflow.net/questions/272198",
"https://mathoverflow.net",
"https://mathoverflow.net/users/110843/"
] | Let $\mathbb{H}$ be hyperbolic plane, $\Gamma$ is a discrete subgroup of $PSL_2(\mathbb{R}$) so that $\Gamma \backslash \mathbb{H}$ is a compact hyperbolic surface. Maybe it will be very simple to you but I am very confused when I try to construct a homeomorphism $\phi: \Gamma \backslash T_1 \mathbb{H} \longrightarrow ... | I'll define the map and leave the proof that it is a diffeo to you. Assume $M$ is a Riemannian manifold and $\Gamma$ is a torsion free group that acts properly discontinuously by isometries on $M$. Get the quotient map $M\to \Gamma\backslash M$.
Check that it is differentiable map between Riemannian manifolds which der... | You only need to think how do you define the structure of Riemannian manifold in $\Gamma \backslash \mathbb{H}$. For this you need an action in the tangent bundle of $\mathbb{H}$ which is same as the one you define to construct $\Gamma \backslash T_1\mathbb{H}$, you can do this because $\Gamma$ is an isometry. So the... | https://mathoverflow.net |
291,355 | [
"https://electronics.stackexchange.com/questions/291355",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/141636/"
] | I am interested in creating a portable diagnostic tool, and as such would like to passively (no wall plug) amplify the 18Vpp sine wave signal that I have (4-7 kHz range) to about 30 Vpp to adequately power a disc style PZT on my device. I have searched extensively and have not been able to come up with a good solution ... | If the frequency was fixed, you could have used a LC resonant tank, but frequency is variable.
So, if you want to passively increase voltage on a signal, pretty much the only solution you have is a transformer.
Another solution would be to use switching converters to get higher DC voltages, and power your signal ampl... | I suggest you to find a suitable transformer, maybe with an amorphous core. Start to compute anything at lowest possible frequency and maximum voltage amplitude, because the flux will be largest at low frequency. Then, if you put a signal with higher frequency or smaller amplitude, anything will still work normally.
| https://electronics.stackexchange.com |
195,696 | [
"https://physics.stackexchange.com/questions/195696",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/1650/"
] | When an exothermic reaction occurs, the energy in the chemical bonds of the reactants is partially transferred to the chemical bonds of the products. The remaining energy is released as heat.
For example:
$$\mathrm{N_2 + 3H_2 \to 2NH_3} \qquad \Delta G^\circ = -32.96 \,\rm kJ/mol$$
Therefore, when $1\,\rm mol$ of ni... | As far as the theory goes, you are absolutely correct, the (negative) binding energy between atoms in a molecule contributes to the total mass of that molecule, so a stable molecule is less massive than the sum of the masses of its constituent atoms.
However (as you yourself calculated), the mass difference is absolut... | Yes, bonds have mass, like every other kind of energy.
This can be significant; if you had a glueball (a hypothetical particle made of massless gluons), it would have mass, and <em>all</em> of the mass would be from the bond energy! Same would go if you somehow managed to bind photons together.
| https://physics.stackexchange.com |
123,285 | [
"https://chemistry.stackexchange.com/questions/123285",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/85472/"
] | I am quite new to the field. So try to figure out what is meant by the equilibrium state of an electrochemical cell?
Is it, where both half cells passing the same number of electrons to either side? if yes, how do the electrons transfer during non-equilibrium state (is it like, there is a net electron transfer due to ... | You should consider the Nernst equation
<span class="math-container">$$
\Delta G = \Delta G^{\ominus} + RT\ln Q=- RT\ln Keq + RT\ln Q
$$</span>
At equilibrium deltaG is zero and Q the reaction coefficient is Keq also note
<span class="math-container">$$
\Delta G = -nFE
$$</span>
so E is zero at equilibrium. Outside e... | An electrochemical cell is producing electricity. So it is out of equilibrium. Reagents which are included in the cell are slowly consumed. The chemical composition of the cell changes, and will slowly tend towards equilibrium. When the reactions are finished, the cell will not produce any electricity later on. The equ... | https://chemistry.stackexchange.com |
291,938 | [
"https://electronics.stackexchange.com/questions/291938",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/127015/"
] | I am currently building a line-following robot for a competition this summer. I have figured out everything except the power.
I expect my robot to draw 7.5 amps in the worst case. now, I've selected a 2S LiPo battery for this, as 7.4 volts is enough for my system. However, I am not sure which capacity to select:
<u... | It depends on your robot and the competition.<br>
If speed is part of the competition, you are much better going for the 300 mAH unit. It's likely that the 300 mAH battery will weigh in at about 20g or less and the 1000 mAH at 60g or more. Carrying 3 times the weight will impact your speed and potentially balance. Most... | i would go with the 1000 mAh. batteries never work efficiently as they should.you have to expect less than the manual says with batteries that is a thing i knew by experience
| https://electronics.stackexchange.com |
271,216 | [
"https://softwareengineering.stackexchange.com/questions/271216",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/128300/"
] | Consider the following singly linked list implementation:
<pre><code>struct node {
std::unique_ptr<node> next;
ComplicatedDestructorClass data;
}
</code></pre>
Now, suppose I stop using some <code>std::unique_ptr<node> head</code> instance that then goes out of scope, causing its destructor to be ... | Yes, this will eventually blow your stack, unless the compiler just happens to apply a tail call optimization to <code>node</code>'s destructor <em>and</em> <code>shared_ptr</code>'s destructor. The latter is extremely dependent on the standard library implementation. Microsoft's STL, for example, will never do that, b... | Late answer but since no one provided it... I ran into the same issue and solved it by using a custom destructor:
<pre><code>virtual ~node() noexcept {
while (next) {
next = std::move(next->next);
}
}
</code></pre>
If you really have a <em>list</em>, i.e. every node is preceded by one node and has at... | https://softwareengineering.stackexchange.com |
493,264 | [
"https://math.stackexchange.com/questions/493264",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/85632/"
] | While using the <em>elementary transformation</em> method to find the inverse of a matrix, our goal is to convert the given matrix into an identity matrix.
We can use three transformations:-<br>
1) Multiplying a row by a constant<br>
2) Adding a multiple of another row<br>
3) Swapping two rows
The thing is, I can't... | First get a non-zero entry in the upper lefthand corner by swapping to rows if necessary. If that entry is $a_{11}\ne 0$, multiply the first row by $a_{11}^{-1}$ to get a $1$ in the upper lefthand corner. Now use operation (2) to get $0$’s in the rest of the first column.
Now get a non-zero entry in the $a_{22}$ posit... | I give you an example of a similar approach to Brian's one.
Start from the matrix
$$A=\left[ \begin{array}{ccc}1&2&0\\2&0&-1\\2&3&-1\end{array}\right]$$
First step is to write the identity matrix on right side of the matrix A.
$$\left[ \begin{array}{cccccc}1&2&0&1&0&0\\2&... | https://math.stackexchange.com |
14,993 | [
"https://astronomy.stackexchange.com/questions/14993",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/11940/"
] | I’ve got a question about white dwarfs and oxygen.
I read in a book that a temperature of 100 million degrees is required to fuse Helium in the core of a red giant. The Helium fuses into Carbon by the triple-alpha process.
It’s also written that, after a temperature of 350 million degrees is reached, the core of a r... | Some oxygen is produced during CNO cycle processing of hydrogen, starting with carbon nuclei. Oxygen is also produced by alpha capture onto carbon nuclei at temperatures well below 350 million K.
Both of these occur in and around the cores of low mass stars before they become white dwarfs. Neon production is not requi... | <h1> Because the Red-Giant Sun can fuse carbon to oxygen </h1>
But, the process is extremely slow. The Sun is too light to actually fuse carbon to oxygen on a large scale. You need much more mass to do that.
So instead, the Sun simply fuses it passively. But the Sun does not do <strong>carbon+carbon=oxygen</strong> fus... | https://astronomy.stackexchange.com |
539,388 | [
"https://electronics.stackexchange.com/questions/539388",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/241568/"
] | For instance, could you get a printed circuit board and connect the cpu to that? I want to connect multiple cheap cpus to each other without spending thousands of dollars on a motherboard that will only hold three or four. If not, what is the actual problem with doing that?
| The question is rather conflicted, so I will address each question raised separately.
In the strictest sense, you could use a CPU without a motherboard. You could do things such as wire wrapping and point-to-point wiring. I've done plenty of wiring like that when I was a teen (though with oscillators and makeshift AM r... | Creating a board from a blank PCB for the processor is pretty much unusable and not worth it.
Because:
<ul>
<li>You need to reverse engineer the entire CPU block.</li>
<li>You need to understand all I/O</li>
<li>You need basically to understand the language code for CPU eg: x86 CPU has much code.</li>
<li>It doesn't wo... | https://electronics.stackexchange.com |
101,554 | [
"https://physics.stackexchange.com/questions/101554",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/15635/"
] | <h1>Semiconductor Optoelectronics:</h1>
What are the differences between multiple Quantum Wells and supperlattices.
| Quantum wells (or more precisely <strong>multi-quantum wells, MQWs</strong>) are nanometer wide layers of a lower band gap semiconductor grown on a higher band gap barrier material. For example GaAs/AlAs layers.
The defining feature of MQWs is that the barriers are wide enough such that wavefunctions in adjacent quan... | Normally, you call a system either MQW or superlattice based on a width of the band formed by interaction of the levels in adjoint QWs. If the bandwidth is small enough (in comparison with temperature, characteristic times, etc., whatever is important for your problem) and you may consider carriers as localized within ... | https://physics.stackexchange.com |
473,390 | [
"https://stats.stackexchange.com/questions/473390",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/48166/"
] | Someone can conduct a t-test and test unidirectional instead of bidirectional. As far as I know, unidirectional testing is not allowed when doing a chi^2-test, correct? If I am right, is it because there is no "directionality" in chi^2-distribution?
Can there be done something similar like chi^2-test that all... | If you consider the form of the classical Pearson chi-squared statistic, as the sum of (observed frequency <span class="math-container">$-$</span> expected frequency)<span class="math-container">$^2$</span> / expected frequency, you can see that the sign of the discrepancy between observed and expected is washed out by... | One of the problems here is that there is no such thing as "the" chi squared test. There are lots of classical hypothesis tests where the null distribution is a chi-squared distribution. If you are referring to the classical Pearson test then that does not have this property --- higher values of the test st... | https://stats.stackexchange.com |
421,728 | [
"https://physics.stackexchange.com/questions/421728",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/203483/"
] | I'm a bit confused about incompressible flow definition. In many textbooks or scientific articles, they simply claim that the incompressibility condition for Navier-Stokes equation is:
$\nabla \cdot \mathbf{u} = 0$
But, nobody says explicitly how to prove that incompressible velocity field should be divergence free.
... | If we look at the mass conservation equation in an Eulerian framework (because it's easier), we have:
$$ \frac{\partial \rho}{\partial t} + \nabla \cdot \rho \vec{u} = 0 $$
Where, if density is constant, obviously $\partial \rho / \partial t = 0$ and then we can factor the $\rho$ out of the derivative and divide, whi... | Physical meaning of divergence is rate of change of control volume per unit volume. If density is not changing then rate of charge of control volume will be zero this is directly from conservation of mass.
| https://physics.stackexchange.com |
270,270 | [
"https://math.stackexchange.com/questions/270270",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/53076/"
] | I'm trying to prove that if $U \in \mathbb{R}^2$ is open and path connected, then for a point $ p \in U$ we have $U \smallsetminus \{p\}$ still path connected.
Start by taking $x,y \in U$. As path connected there exists continuous $\gamma : [0,1] \to U$ such that $\gamma (0) = x$ and $\gamma(1) = y$.
Take $p \in U$. ... | Your idea is good, but the proof is not rigourous enough.
<ol>
<li>You should choose $\delta>0$ such that $\delta < \min\{\|x-p\|, \|y-p\|\}$ and $B(p,c\delta)\subset U$ for some $c>1$. The first condition is needed because you want to keep $x$ and $y$ outside the open disc. The second condition is needed, ot... | This is a comment: what if one of or both $x, y$ are inside the open nbd you have picked?
<strong>added</strong> How about this: Pick a point $q$ different from $p$ and consider the set of points in $U-\lbrace p \rbrace$ that can be path connected to $q$. This set and its complement are both open. If the complement is... | https://math.stackexchange.com |
339,405 | [
"https://softwareengineering.stackexchange.com/questions/339405",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/93096/"
] | I'm looking for some assistance and ideas for developing an algorithm for choosing random soccer teams based on the skill levels of the participating players.<br>
What I have so far is a list of particpating players with arbitrary skill levels between 1 and 100. e.g.
<pre><code>PlayerA: 30,
PlayerB: 45,
PlayerC: 50,
P... | <ol>
<li>Break down users into buckets (owned-it, expert, immediate, beginner, noob)</li>
<li>Randomly split the people into two teams from each bucket</li>
<li>Any remainders left from each bucket are randomly assigned. </li>
</ol>
Note that you're trying to make things not skewed one way or the other and, hence, in ... | I suggest a time-boxed approach.
<ol>
<li>Generate two random teams using whatever method you have been using</li>
<li>Compute the total skill of both teams, and take the difference</li>
<li>If the difference is 0, your teams are perfectly balanced. Exit.</li>
<li>Trade two random team members and recompute the total... | https://softwareengineering.stackexchange.com |
6,918 | [
"https://electronics.stackexchange.com/questions/6918",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/588/"
] | How can I design a system that would allow me to put multiple receivers on a single 4-20mA current loop? Assume that I have design control over only one of the receivers.
Sensor:
<ul>
<li>Loop powered (2-wire)</li>
<li>Supply voltage: 12-28VDC</li>
<li>Max Load: 250 Ohms @ 12VDC (500 Ohms @ 24VDC)</li>
</ul>
Current... | Current loops were initially designed to connect multiple teletypewriters in series (originally 60 ma was used instead of 20 ma). This scheme was latter adapted for instrumentation use, with 4-20 ma as the standard.
In your current receiver design, one end of the resistor is connected to ground. Instead it should be... | As the sensor you are using has a maximum load I think that one (maybe good) alternative is use a hall sensor on the loop. This way you can extract the information on the current without interfering in the main loop. The other receiver can be a regular one.
| https://electronics.stackexchange.com |
266,223 | [
"https://softwareengineering.stackexchange.com/questions/266223",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/102768/"
] | <pre><code>--------------------- ----------------------
| FLIGHT | | STEWARD |
--------------------- ----------------------
| Arrival time | | Steward ID |
| Departure time | | Name |
| Flight ID | ----------------------
---------------------... | <blockquote>
<ol>
<li>I am doubting what I should name my association. Should it be "a flight has * stewards"? Or should it be "a steward works on many flights"?</li>
</ol>
</blockquote>
Usually, the more specific you can name your association, the better, because a more specific name conveys more information.
... | In my eyes there is no such thing as a Many to Many relationship. There is a crucial concept that is lost in the shuffle when you rely on a many to many relationship.
Let's look at a diagram I made for your scenario
<img src="https://i.stack.imgur.com/2PsIB.png" alt="Flight/Assignment Diagram">
In here I've modeled y... | https://softwareengineering.stackexchange.com |
732,178 | [
"https://math.stackexchange.com/questions/732178",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/125459/"
] | Let $F$ be a finite field of characteristic $p$. Show that every element of $F$ is algebraic over $\mathbb{Z}_p$.
Since char$(F)$ = $p$, $\forall a \in F $ not zero, $ap$ = 0. We also have the same characteristic for $\mathbb{Z}_p$.
How can I use the prime characteristic to show there is a polynomial $P(x) \in \mathb... | As $F$ is finite, every element of $F^*$ has finite (multiplicative) order. So, for $\alpha \in F^*$, there is some $n \in {\mathbb N}$ such that $\alpha^n = 1$, making $\alpha$ a root of $X^n - 1 \in {\mathbb Z}_p[X]$.
(In fact, $F^*$ is cyclic and you can take the same $n$ for all elements of $F^*$.)
Alternatively,... | For every polynomial $f(x)$ over $\mathbf{F}_p$, the value $f(a)$ is also in $\mathbf{F}_p$.
There are infinitely many such polynomials, but only finitely many possible values for $f(a)$. In particular, there must be two polynomial $f(x)$ and $g(x)$ such that $f(a) = g(a)$. Can you use this information to find a polyn... | https://math.stackexchange.com |
372,868 | [
"https://electronics.stackexchange.com/questions/372868",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/188053/"
] | How do we find the Q-factor of a fourth order active-RC filter? The filter in question is not developed by cascading lower order filters.
| Serial communication is transmitting data one byte at a time. Your code is fast enough to read and process one byte before the next one is received.
There are many possible solutions to this, and using delays is not a good one.
You could send a marker character at the end of each command, e.g. <code>LED_ON!</code>. T... | @9600 Baudrate, you are receiving data at 10 bits per millisecond. One character is 8 bits + start and stop bits in a frame. You are reading the buffer faster than it. So a simple solution would be to put a delay of > 1 ms or so after serial read(), inside the loop.
| https://electronics.stackexchange.com |
335,945 | [
"https://physics.stackexchange.com/questions/335945",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/70392/"
] | I am slightly confused why the decay $\pi^0 \rightarrow \gamma \rightarrow e^-e^+$ is forbidden. A naive guess would say that the intemediate photon $\gamma$ has a spin 1, the initial pion has a spin $0$ therefore this violates spin conservation. However, on the same reasoning $\pi^+\rightarrow W^+ \rightarrow e^+ \nu_... | The QCD and QED themselves conserve parity. The conclusion of this statement is that all corresponding effective vertices must conserve the parity. The only coupling of $\pi^{0}$ to $\gamma$ conserving the parity is
$$
L_{\pi^{0}} \simeq \frac{\pi^{0}}{\Lambda}\epsilon^{\mu\nu\alpha\beta}F_{\mu\nu}F_{\alpha\beta},
$$
... | your question could be generalized: pion decays to odd number of photon is forbidden. That's a conclusion of Furry's theorem: even number of photons is forbidden to odd numbers of photon
Here the only assumption is that strong interaction and EM process charge conjugation symmetry.
As for the second process, because ch... | https://physics.stackexchange.com |
3,727,940 | [
"https://math.stackexchange.com/questions/3727940",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/593295/"
] | Suppose <span class="math-container">$\mathscr{B}$</span> is the cylindrical <span class="math-container">$\sigma$</span>-algebra on <span class="math-container">$\mathbb{R}^{[0,1]}$</span>. Let <span class="math-container">$C:=C[0,1]$</span> and <span class="math-container">$\mathscr{A}:=\{B\cap C: B\in\mathscr{B}$</s... | <span class="math-container">$$B := \bigcup_{k \ge 1} \bigcap_{N \ge 1}\bigcup_{n \ge N} \bigcup_{\substack{\alpha_0,\dots,\alpha_{n-1} \in \mathbb{Q} \\ \frac{1}{n}(\alpha_0+\dots+\alpha_{n-1}) \le 1-\frac{1}{k}}} \left\{f : [0,1] \to \mathbb{R} \hspace{1mm} | \hspace{1mm} \left|f\left(\frac{j}{n}\right)-\alpha_j\righ... | <strong>Hints:</strong>
<ol>
<li>Recall (or show) that <span class="math-container">$\mathcal{A}$</span> is the Borel <span class="math-container">$\sigma$</span>-algebra generated by the uniform topology on <span class="math-container">$C[0,1]$</span>.</li>
<li>Show that the set <span class="math-container">$A$</span>... | https://math.stackexchange.com |
409,521 | [
"https://physics.stackexchange.com/questions/409521",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/194291/"
] | Suppose a charge $q$ is experiencing a force due to charge $Q$. Suppose we move the charge $Q$ very slowly (no acceleration) what's the instantaneous impact on the charge $q$? How will the $q$ react?
| No two things in the universe happen "instantaneously", unless they are at exactly the same location, because "instantaneously" would have different meanings for observers moving at different velocities. Maxwell's equations, which describe electromagnetic interactions perfectly for most practical purposes, contain tim... | If you accelerate Q, then you will create a changing electric field, which creates a changing magnetic field, which create a changing electric field, etc., and the result will be EM waves emanating from Q, and they will travel at c to q, changing the force on q when they arrive.
But if there's no acceleration, there's... | https://physics.stackexchange.com |
511,475 | [
"https://electronics.stackexchange.com/questions/511475",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/258104/"
] | The electric company was working on the power lines for four days out in the woods, so they put our street on huge diesel generators (each was the size of a small car) that ran constantly to supply us with power. Everything worked fine, but I noticed some anomalies:
<ul>
<li>My roof solar panels were not working.
</li>... | It sounds like the voltage and frequency of the temporary generator power were both overly high.
<ul>
<li>Grid-tied solar power systems measure the frequency and voltage of incoming power and do not supply their own if it is not within expected ranges. This is for a number of reasons that can be generally described as ... | The standby mains voltage and frequency would not be as stable as the grid.Where would exported solar energy go if the neighbours were not drawing much power ?.The voltage waveform would probably have more harmonics present .This is why the power is not as good .Also the power is expensive to generate .
| https://electronics.stackexchange.com |
58,427 | [
"https://mathoverflow.net/questions/58427",
"https://mathoverflow.net",
"https://mathoverflow.net/users/13641/"
] | True or false: If G is special 2-group, then |G:Z(G)| is a square.
Recall that G is a special p-group if Z(G) = G' = Frat (G) be elementary abelian. The above assertion is true, whenever |Z(G)| = 2, that is, G is an extra-special 2-group.
Thank you.
| Being systematic a $2$-special group is specified completely by two $\mathbb Z/2$-vector
spaces $U=G/Z(G)$ and $V=Z(G)$ together with the induced square map $\Gamma^2U\to V$
which is non-degenerate in the following sense: We have an injective map $\Lambda^2U\to\Gamma^2U$
mapping $u\land v\mapsto\gamma_1(u)\gamma_1(v)$ ... | This is false.
Let $G = E_{16} \rtimes C_2$, where $E_{16}$ denotes the elementary abelian group of order $16$. Then $G$ is special, but $Z(G) \cong C_2 \times C_2$ has index $8$ in $G$.
| https://mathoverflow.net |
46,272 | [
"https://softwareengineering.stackexchange.com/questions/46272",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/16625/"
] | I'm working as a web developer and I want to be able to determine if I'm efficient.
Does this include the how long it take to accomplish tasks such as:
<ul>
<li>Server side code for the site logic with one language or multiple php,asp,asp.net.</li>
<li>Client side code like javascript with jquery for ajax, menus and ... | There is a lot to be said for detailed requirements. Everyone hates creating requirements documents but they are a very necessary evil. That being said, I've managed a lot of software projects over the years and I have a few methods that I've found make it much easier to estimate.
Personally I can't say enough about... | <blockquote>
How can i judge how long it will take to complete a website?
How can I estimate how long the job will take, and how can I calculate the required time to finish any new projects?
</blockquote>
You can't.
Make up a schedule you feel comfortable with.
The best you can do is make small deliverables (weekly, ev... | https://softwareengineering.stackexchange.com |
403,439 | [
"https://electronics.stackexchange.com/questions/403439",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/202501/"
] | I have grip warmers on a bike. basically just heat tape. I would like to reduce the supply voltage from lithium battery from 18 vdc to 12 vdc. My goal is to reduce warmer element temperature and increase battery life. What is the simplest way to do this? thanks!
| A resistor dropping 18 down to 12V wastes <span class="math-container">\$1\over3\$</span> of the energy.
A DC-DC buck converter can be about 90 percent efficient, but the cheap ones typically get about 85% - wasting about <span class="math-container">\$ 1\over 6\$</span>, but PWM can improve on that by removing the i... | Adding a resistor half the resistance of the elements will get you down to 12V, and increase battery life by 50%, but you end up wasting a third of the energy in the battery (unless you use that resistor to keep something else warm). There are cheap DC-DC buck converter modules available, that will regulate down to 12V... | https://electronics.stackexchange.com |
484,065 | [
"https://physics.stackexchange.com/questions/484065",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/47467/"
] | What I understand:
<ol>
<li>In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt</li>
<li>I understand that a watt is a unit of power (change in energy per unit time) that describes the rate at which physical work can be done</li>
<li>Reactive power is power for whi... | What you understand is basically correct. Regarding DC circuits it is important to point out that 1 watt = 1 amp x 1 volt under steady state (long time) conditions when transients are gone. Under those conditions an ideal capacitor looks like an open circuit (no current flow) and an ideal inductor looks like a short-ci... | <blockquote>
I understand that a watt is a unit of power (change in energy per unit time) that describes the rate at which physical work can be done
</blockquote>
Right.
The key thing to observe is that energy can move in both directions. It can move from the "supply" to the "load", but it can also move from the "l... | https://physics.stackexchange.com |
359,573 | [
"https://softwareengineering.stackexchange.com/questions/359573",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/285950/"
] | I have a try/catch block which looks like this :
<pre><code>try {
geoms.add(convertLineToGeom(ln));
} catch(IllegalArgumentException e) {
System.out.println("ligne n°" + counter + " : " + e.getMessage());
}
</code></pre>
My function convertLineToGeom might throw different exceptions that I made myself, all of... | There is no point in forcing your callers to use a complicated type expression for this purpose. They expect to get an <code>IllegalArgumentException</code> as usual, and the fact that you are delivering helpful subclasses of this standard type shouldn't impose more burdens on the caller, since the normal <code>catch(I... | <pre><code>As yourself not which is the best to *throw* ...
As yourself which is the most useful to *catch*!
</code></pre>
Why do we have multiple Types of Exception?
So that the catching code can <em>handle</em> them differently.
If all you want to do is put a message on the screen and kill the program stone de... | https://softwareengineering.stackexchange.com |
166,234 | [
"https://mathoverflow.net/questions/166234",
"https://mathoverflow.net",
"https://mathoverflow.net/users/31045/"
] | Let $G$ be a finite group such that $G$ has a normal subgroup $H$ and $H$ is isomorphic to the alternating group $A_5$. Also we know that $G/H \cong A_5$.
Can we say that $G \cong A_5\times A_5$?
Thanks for your helps
| Well, $G$ must be isomorphic to the direct product $A_{5} \times A_{5}$ in any case, under your assumptions, since the outer automorphism group of $A_{5}$ just has order $2$. Note that $H$ is a maximal normal subgroup of $G,$ and that $F(G) = 1$ under your assumptions. If $G \not \cong A_{5} \times A_{5},$ then $H = F^... | This is essentially the same proof as Geoff's, but in different language. The action of $G$ on $H$ by conjugation gives a homomorphism $\rho\colon G\to\text{Aut}(H)$ whose kernel is the centralizer $C_G(H)$. The image $\rho(G)$ is a subgroup of $\text{Aut}(H)\cong S_5$ which contains $\rho(H)\cong A_5$, so $C_G(H)$ h... | https://mathoverflow.net |
250,833 | [
"https://softwareengineering.stackexchange.com/questions/250833",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/5800/"
] | A friend has written a programming language. It has a syntax reminiscent of SGML. He has written an interpreter for it, and an IDE. He and his colleagues use it in-house as a server-side language. It can also be used to write command-line tools.
He wants to make it available to the public, in the expectation that peo... | The answer is yes, and no. It depends on the commercial motivations of potential customers and the attributes of the language and the problems it solves.
No, the world does not need another general purpose computing language created by an individual or a small team. When Perl, Python, Ruby, Java and Javascript and wer... | Does his language do something that enough people will pay for?
That's really the only thing that decides whether a business model will work. Do you have a large market of users who are large enough not to worry about licensing costs? Does the language support devices or standards that the customers can't live withou... | https://softwareengineering.stackexchange.com |
95,462 | [
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] | I am trying to understand the uniformly most powerful (UMP) equivalence tests presented by Welleck (2010) with respect to $p$-values for the tests. In the case of the paired $t$ test example concerning measures before and after an intervention (pp 94–96) Wellek presents a UMP one-sample $t$ test of mean equivalence wit... | Calculating the $p$-values for asymmetric equivalence bounds is a nested process. First, one has to set up the procedure to find the critical values for each $\alpha^*$. Note that this $\alpha^*$ is not the intended type I error but a placeholder for any such level. Then, one has to find the $\alpha^*$ such that one of... | For all kinds of tests, the $p$-value can be imagined as the particular $\alpha$ for which the present data's test would be on the edge between significance and nonsignificance. In other words: The $p$-value is the $\alpha$ that makes the critical value coincide with the test statistic. So if the test statistic of your... | https://stats.stackexchange.com |
593,039 | [
"https://physics.stackexchange.com/questions/593039",
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"https://physics.stackexchange.com/users/209383/"
] | Consider a metal stick, say iron or aluminum. From the experience, even if it's resilient, bend it forward and backward a couple of times, it would be broken.
However, consider a thin iron foil or thin aluminum foil. From the experience, we know that it could be bend forward and backward for almost as many time as time... | Almost all solid metals are made up of individual small crystals called grains. A small stretching movement will simply stretch the crystal lattice of each grain a little, so the whole thing bends.
When you flex thin foil, it is so thin that the stretching distance is small and the grains can deform to match.
But with ... | Let me use just a simple geometrical reason.
You can in principle bend a monodimensional row of bound particles to a wide angle affecting only the angle of the bond at about the pivotal point.
Conversely, if you bent a 2-D ensemble of particles (variously bound, it can be multiple rows as above slightly interacting or ... | https://physics.stackexchange.com |
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