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 |
|---|---|---|---|---|---|
601,918 | [
"https://math.stackexchange.com/questions/601918",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/114971/"
] | Given a set of $m$ orthogonal vectors $\{\phi_1, \dots, \phi_m\}$
show that if you form any $n>m$ linear combinations of them :
$$
\begin{align}
v_1 & = a_{11} \phi_1+ \dots+ a_{1m} \phi_m \\
v_2 & = a_{21} \phi_1+ \dots+ a_{2m} \phi_m \\
& \vdots \\
v_n & = a_{n1} \phi_1+ \dots+ a_{nm} \phi_m
\end{... | Here is an approach. Assume for simplicity they are orthonormal ($\langle \phi_i,\phi_j\rangle =\delta_{ij}$). Now, we follow the steps
<strong>step 1:</strong> construct the vectors
<blockquote>
$$ v_k = \sum_{i=1}^{m}a_{k i} \phi_i \quad k=1,2,\dots n, $$
</blockquote>
which are the linear combinations of the ... | Let $W=\operatorname{span}(\phi_1, \dots, \phi_m)$ and $U=\operatorname{span}(v_1,\dots,v_n)$. $\dim W=m$ because the vectors are orthogonal, and $U \subseteq W$. This implies that $\dim U\leq \dim W$. But $n > m$, so the vectors cannot be linearly independent.
| https://math.stackexchange.com |
71,970 | [
"https://security.stackexchange.com/questions/71970",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/59842/"
] | I've recently been reading on session cookies and how they can be hijacked via man-in-middle attacks. It seems this is mainly possible on an unencrypted connection between a client and a webserver.
However, I cannot figure out why, if one is already 'in the middle' of an unencrypted connection, would one prefer to cap... | There are 2 main reasons why cookies are easier to steal than login credentials:
<strong>Cookies are sent for every request, login credentials are only sent once for each "session"</strong>
If you sniff a network, it is less likely that you will be in place at the point when a user actually perform a login using its ... | <em>If</em> the username and password were sent in plaintext, then yes, sniffing them is a better option.
However, a common pattern is for the login process to be encrypted (for security), and then the remainder of the session takes place in the clear (because encryption imposes a bit of a performance penalty). In su... | https://security.stackexchange.com |
192,476 | [
"https://physics.stackexchange.com/questions/192476",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/55707/"
] | The following question is from David Griffiths' <em>Introduction to Quantum Mechanics</em>:
<blockquote>
<strong>Problem 2.13</strong> A particle in the harmonic oscillator potential starts out in the state
$$\Psi(x,0) = A[3 \psi_0(x) + 4 \psi_1(x)]\,.$$
(a) Find $A$.
(b) Construct $\Psi(x,t)$ and $|\Psi(x,... | <blockquote>
But how can we guarantee that two solutions $\boldsymbol {\psi_1}$ and $\boldsymbol {\psi_2}$ to the time-dependent equation don't have $\boldsymbol {\psi_1(x,0)} = \boldsymbol {\psi_2(x,0)}$. If we can't guarantee this, then how do we know that the solution found by Griffith's method is unique?
</blockq... | The form of the solution shown by Griffiths is <strong>not</strong> unique. That means that there exist cases where a basis $\{\psi_n(x)\}$ will reproduce $\Psi$ as
$$
\Psi(x,t)=\sum_{n=1}^\infty c_n\psi_n(x) e^{-iE_nt/\hbar},
$$
but there exists a second, different basis $\{\varphi_n(x)\}$ which (with different coeffi... | https://physics.stackexchange.com |
231,136 | [
"https://softwareengineering.stackexchange.com/questions/231136",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/119554/"
] | This is partly genuine curiosity, and partly a check on my understanding. I'm probably missing the point.
In Haskell, why does a monad use operations called <code>return</code> or <code>unit</code> to describe putting a type into the container -- lifting it into the monadic space? It seems more intuitive to call the o... | The term <code>unit</code> comes from category theory where we define a monad as two natural transformations <code>unit : Identity ~> m</code> and <code>join : m x m ~> m</code>. In case you're curious, <code>bind f = join . fmap f</code>.
<code>return</code> comes from do notation where <code>return</code> look... | As Benjamin Hodgson mentioned in his comment, the term <em>lift</em> is usually applied to lifting non-monadic functions into the monad.
As for why the function is specifically called <code>return</code>, that is because it is used in the <code>do</code> syntactic sugar, which is meant to resemble an imperative C/ALGO... | https://softwareengineering.stackexchange.com |
2,292,581 | [
"https://math.stackexchange.com/questions/2292581",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/335742/"
] | Can somebody please check my working?
<strong>The variable $y$ depends on $x$ and $x$ and $t$ are related by $x=e^t$</strong>
<strong>Show that $x\frac{dy}{dx}=\frac{dy}{dt}$</strong>
$$x=e^t$$
$$dx=e^t dt$$
$$\frac{dx}{dt}=e^t=e^t\times1=e^t \times\frac{dy}{dy}$$
$$\frac{dx}{dt}\times\frac{dy}{dx}=x\frac{dy}{dy}\tim... | In your answer, I am not sure how to get from line (3) to line (4).
I would proceed using the Chain Rule:
$$
\frac{dy}{dt} = \frac{dy}{dx} \frac{dx}{dt}
$$
but you know how $x$ depends on $t$, can you find $dx/dt$ and plug in?
| You are given $$y=f(x),x=e^t.$$
Then
$$\frac{dy}{dx}=f'(x)$$ and by the chain rule,
$$\frac{dy}{dt}=\frac{dy}{dx}\frac{dx}{dt}=f'(x)e^t=f'(x)x,$$ hence the claim.
| https://math.stackexchange.com |
73,250 | [
"https://electronics.stackexchange.com/questions/73250",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/20646/"
] | I would like to have a RTC alarm turn on my arduino at a specified time each day. I know that Arduino has good sleep modes but I'm concerned even with the quiescent power consumption from the voltage regulator due to feeding Arduino with 9V (this is my only option). My preference is to completely shut off the arduino b... | The 5V rail will most definitely be able to supply the power that you need in your setup. For most ATX PSUs, the +5v rail has the largest current capacity of all rails on the supply. Many, if not most devices will charge as soon as there is a voltage applied to their USB port, so I'd say that aspect of your setup is al... | Your circuit is ok. The USB connector is connected to your ATX PSU so the power limit is determined by the PSU. You can obtain the maximum current available in the 5 V line from the datasheet of your PSU. Usually there is a sticker on the power supply which gives the maximum current for each line.
Remember that modern... | https://electronics.stackexchange.com |
146,721 | [
"https://electronics.stackexchange.com/questions/146721",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/62736/"
] | I moved in to a rental home that only has 240 VAC available. Now I am faced with the task of connecting a sauna that ran on 340 V+ and an older 3 phase motor that was used for some hobby gear.
I have heard rumors that it is possible to run two 240v lines in series to make this happen. I am in Germany if that is needed... | I didn't know that there were 340V systems around on this planet.
Europe, including Germany has 400V 3Ph+N or 230V 1Ph+N power supply connections for domestic use. In some EU countries older pre-WWII estates still have 3-Ph 230V without neutral grids.
Connecting a 340V system is impossible. You could make use of ... | Europe uses 3 phase wye 220V/380V 4 wire system. (3 phases and a neutral)
Line to neutral is 220V, line to line 380V.
The house may not have 380V outlet, but the voltage may be coming to the house.
I would recommend getting a qualified help with that.
| https://electronics.stackexchange.com |
99,499 | [
"https://math.stackexchange.com/questions/99499",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/19793/"
] | <span class="math-container">$\sum_{n \in \mathbb{N}} \lVert f_{n}-f \rVert_{1} < \infty$</span> implies <span class="math-container">$f_{n}$</span> converges almost uniformly to <span class="math-container">$f$</span>, how to show this?
EDIT: Egorov's theorem is available. I have been able to show pointwise a.e. co... | Put $g_n:=|f_n-f|$, and fix $\delta>0$. We have $\sum_{n\in\mathbb N}\lVert g_n\rVert_{L^1}<\infty$ so we can find a strictly increasing sequence $N_k$ of integers such that $\sum_{n\geq N_k}\lVert g_n\rVert_1\leq \delta 4^{-k}$. Put $A_k:=\left\{x\in X:\sup_{n\geq N_k}g_n(x)>2^{1-k}\right\}$. Then $A_k\subset... | Suppose <span class="math-container">$\sum_{n=1}^{\infty} \|f_n - f\|_{L^1} < \infty$</span>, where
<span class="math-container">\begin{align} \|f_n - f\|_{L^1} = \int_{X}|f_n(x) - f(x)| dx. \end{align}</span>
Let <span class="math-container">$k \geq 1$</span>. By the absolute summability assumption, for a sufficien... | https://math.stackexchange.com |
367,660 | [
"https://electronics.stackexchange.com/questions/367660",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/148421/"
] | I am confused as to how to choose the receiving end voltage for a short line approximation
For example if i have a 220kV transmission line at 50Hz at 60Km. At the end of teh line theirs a load of 50MW and the lines impedance is Z=5+6j. The question asks find the sending end voltage using Vs=VR+ZIR. I can do the calcu... | I find that the concept of sending/receiving end voltage is somewhat meaningless in most cases. Actual transmission lines are connected in complex networks with distributed impedance (the line itself) and point impedance (loads tapped off) all over the network. There is no set beginning or end.
In the real world ... | You say: -
<blockquote>
The question asks find the sending end voltage
</blockquote>
If you are given a voltage and a line length and a line impedance then clearly the voltage you have been given (220 kV) is the voltage at the end of the line feeding the 50 MW load.
There can be no other reasonable options. Make y... | https://electronics.stackexchange.com |
54,562 | [
"https://cs.stackexchange.com/questions/54562",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/42518/"
] | I wrote pseudocode for <code>Selection Sort</code>, but I'm not sure what is the running time of my algorithm, can you help me with that?
<hr>
<strong>My Pseudocode: Selection Sort(int a[], int n)</strong>
Input: array of length $n$
Output: sorted array
<pre><code>for r=1 to n
min=a[r]
for i=r to n
... | If the body of the outer loop gets executed $A$ times and the body of the inner loop gets executed $B$ times, then your algorithm runs in time $\Theta(A+B)$. After calculating $A$ and $B$, you will discover that $B$ grows faster than $A$, and so the running time of your algorithm is dominated by the number of times the... | The inner loop will iterate $n - r + 1$ times for each iteration of the outer loop. To find the total runtime, we can sum this expression over $r = 1$ to $r = n$:
\begin{align*}
\sum_{r = 1}^{n} (n - r + 1) &= n^2 - \left(\sum_{r = 1}^{n} r\right) + n \\
&= n^2 - \frac{n(n + 1)}{2} + n \\
&= \frac{1}{2}n^2 ... | https://cs.stackexchange.com |
153,511 | [
"https://physics.stackexchange.com/questions/153511",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/67797/"
] | Newton's third law says "for every action, there's an equal and opposite reaction." So why is it, say, that when a pool/billiards ball hits the wall of the table, the ball doesn't just turn around?
| Note that in your suggested motion after the collision, momentum would not be conserved. The Law of Conservation of Momentum is kind of a big deal in Physics, and especially useful when analyzing collisions. It states that for a closed system, momentum is conserved. It's also sometimes restated that for a closed system... | The force from the ball on the wall is exactly equal and opposite to the force of the wall on the ball. Both forces however are perpendicular to the wall (and must be assuming the wall is frictionless) and <em>not</em> necessarily perpendicular to the ball's initial direction of motion. Being perpendicular to the wall ... | https://physics.stackexchange.com |
3,078,095 | [
"https://math.stackexchange.com/questions/3078095",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/596291/"
] | <strong>Problem</strong>: Given 20 distinct positive integers, not greater than 70. Show that among their pairwise differences, at least four are equal.
<strong>Solution given by the professor</strong>: We may assume that the numbers form an increasing sequence:<span class="math-container">$1 \leq a _ { 1 } < a _ {... | You want to minimize the telescopic sum for <span class="math-container">$a_{20}$</span>:
<ul>
<li>What is the minimal value for <span class="math-container">$a_1$</span>? <span class="math-container">$1$</span>!</li>
<li>How do we minimize the <span class="math-container">$19$</span> differences under the given const... | Consider <span class="math-container">$a_1=1$</span>, then:
<span class="math-container">$$71=1+(1)+(1)+(1)+\\
\qquad \qquad (2)+(2)+(2)+\\
\qquad \qquad(3)+(3)+(3)+\\
\qquad \qquad(4)+(4)+(4)+\\
\qquad \qquad(5)+(5)+(5)+\\
\qquad \qquad(6)+(6)+(6)+\\
(7)\le \qquad \qquad \ \ \ \\
a_1+(a_2-a_1)+(a_3-a_2)+(a_4-a_3)+\\
\... | https://math.stackexchange.com |
331,638 | [
"https://stats.stackexchange.com/questions/331638",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/192244/"
] | I need to cluster datapoints that are represented as a binary vector, using hierarchical cluster.
I chose the manhattan distance and am trying to figure out how to choose the "best" linkage method. I heard that Ward should not be used since it relies on euclidean distance. Is it true? I have not found any "real scienti... | There is no universal "best". It's your <em>choice</em>.
For example, <em>complete linkage</em> may be nice, because it means any two instances have at not h bits different at height h.
Or you may want <em>average linkage</em>, so that the average number of bits is h.
Or you may want <em>minimax linkage</em>, so tha... | I suppose I would employ <strong>cophentic correlation</strong> to identify which of the linkage methods mentioned above produces the dendrogram with the highest similarity to the underlying distance matrix.
The distance between two objects in your dendrogram and their first horizontal link, i.e. the point at which th... | https://stats.stackexchange.com |
75,132 | [
"https://electronics.stackexchange.com/questions/75132",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/26011/"
] | I use Eagle Cad 6.4 to prepare PCB layouts then manufacture them at home. As I use amateurish equipment and method, I would like to have bigger pads as much as possible so that when I drill the pad holes, I will have a very large ring of copper around the hole to solder. It would be convenient to have bigger pads (whe... | EAGLE has no say over the outcome of the thickness of the actual copper layers themselves, since you'll be etching the board yourself and you're the one picking the copper board stock. However, you can increase the size of the annular ring to give yourself more room to drill a hole close to the center of a PTH.
Using... | To have a minimum annular ring at pads, open your DRC in the PCB window, go to the RESTRING tab and set there the minimum for your pads in top, bottom (I guess you are not using inner layers). For my experience with DIY pcbs, a value over 12 mils works.
Note: take care as this can create pad-to-pad clearance violation... | https://electronics.stackexchange.com |
104,107 | [
"https://stats.stackexchange.com/questions/104107",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/44795/"
] | When plotting two kernel desitiy estimates into the same frame
<pre><code>plot(density(all4[,3],kernel="epanechnikov"),col='red',ylim=c(0,0.4),xlim=c(-50,50))
lines(density(all2[,3],kernel="epanechnikov"),col="blue",ylim=c(0,0.4),xlim=c(-50,50))
</code></pre>
the result looks like this:
<img src="https://i.stack.img... | <strong>The problem is discretization error.</strong>
<code>density</code> divides the range of data by default into <code>n=512</code> intervals. The outlier causes the intervals to be at least an order of magnitude greater than otherwise. With very large amounts of data (it seems to take somewhere more than $10^5$... | The only think I can think of is that the bandwidth selected with the outliers left in is very small and your "red" density is just a bunch of peaks at the data points. However, since it is only evaluated at n=512 points and the plot function just joins the function values it appears smoothed and with higher values eve... | https://stats.stackexchange.com |
11,760 | [
"https://physics.stackexchange.com/questions/11760",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | Landau writes "It is found, however, that a frame of reference can always be chosen in
which space is homogeneous and isotropic and time is homogeneous."
Does he mean that we can prove the existence of an inertial frame or does he want to say that it is assumed by doing enough number of experiments?
Can we start wit... | I believe this is just a restatement of the first Newton's law.
| The edition Mechanics was 1st published at 1960 and was written earlier than that.
Landau died in 1968 aged 60.<br>
Just 4 years before, in 1964, the CMB was discovered and the properties of it was unknown for years after.<br>
It appears that Landau's saying was vindicated with a referential with the properties of th... | https://physics.stackexchange.com |
168,929 | [
"https://stats.stackexchange.com/questions/168929",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/86911/"
] | I am running an analysis on the probability of loan default using logistic regression and random forests.
When I use logistic regression, the prediction is always all '1' (which means good loan). I have never seen this before, and do not know where to start in terms of trying to sort out the issue. There are 22 co... | Well, it does make sense that your model predicts always 1. Have a look at your data set: it is severly imbalanced in favor of your positive class. The negative class makes up only ~7% of your data. Try re-balancing your training set or use a cost-sensitive algorithm.
| The short answer is that logistic regression is for <em>estimating probabilities</em>, nothing more or less. You can estimate probabilities no matter how imbalanced $Y$ is. ROC curves and some of the other measures given in the discussion don't help. If you need to make a decision or take an action you apply the los... | https://stats.stackexchange.com |
284,822 | [
"https://dba.stackexchange.com/questions/284822",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/148012/"
] | I've built application that compares objects in the databases and generates scripts to replicate objects in the different DB. What I've noticed while I was using this to retrieve view code
<pre><code>select * from INFORMATION_SCHEMA.VIEWS where TABLE_NAME = 'V_SC_ALL_CUSTOMER_DOCUMENTS'
</code></pre>
is that <code>VIEW... | As Erik mentioned in the article he linked, <code>INFORMATION_SCHEMA</code> is a deprecated schema from the classic days of SQL Server 2000. You should read the article he linked as it goes through the reasons it's deprecated, and cites Microsoft's docs that support those reasons.
You can instead use the following quer... | FWIW, I worked a bit on the info schema views back in the days. Among other things I created a database diagram for them (which I probably still have lying around, somewhere).
Then came 2005, and I realized how out-of-phase they were with the product. Just consider the number of catalog views (approx 280) with how many... | https://dba.stackexchange.com |
819,521 | [
"https://math.stackexchange.com/questions/819521",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/146944/"
] | <blockquote>
If $m$ and $n$ are positive real numbers satisfying the equation $$m+4\sqrt{mn}-2\sqrt{m}-4\sqrt{n}+4n=3$$
find the value of $$\frac{\sqrt{m}+2\sqrt{n}+2014}{4-\sqrt{m}-2\sqrt{n}}$$
</blockquote>
I came across this question in a Math Olympiad Competition and had no idea how to solve it. Can anyone he... | It can be helpful to get rid of the square root symbols. If you let $m=x^2$ and $n=y^2$ with $x$ and $y$ understood to be positive, the equation becomes $x^2+4xy-2x-4y+4y^2=3$, which can be rewritten as
$$(x+2y)^2-2(x+2y)=3$$
or
$$u^2-2u-3=0\qquad\text{with}\quad u=x+2y$$
The quadratic factors as $(u-3)(u+1)=0$. Re... | The trivial answer is to realize that m = 1 and n = 1 meets the first criteria, so you can use those in the second equation.
But that's not much fun.
| https://math.stackexchange.com |
263,871 | [
"https://dba.stackexchange.com/questions/263871",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/48093/"
] | I am using:
SSMS-18.4
SQL Server-SQL 2019 CU3
Windows 10
I was able to create a linked server successfully from on-premise SQL 2017 to the Azure SQL database without exposing my password.
<pre><code>--Read the password from text file
DECLARE @password VARCHAR(MAX)
SELECT @password = BulkColumn
FROM OPENROWSET(B... | Depending on how you create the text file, it can be in all sorts of formats. Unicode or ANSI. With or without a Byte order Mark. With or without trailing whitespace and line feeds, either posix or Windows style.
JSON is simpler that way.
For instance if you run cmd.exe
<pre><code>c:\>echo CowboYs4EVR! > ... | I have just reproduced your scenario and in my environment, it works. The only issue I could think of might be the reading of the text file. Could you maybe:
<ul>
<li>try changing from SINGLE_BLOB to SINGLE_CLOB to ensure that it is read as a varchar(max) and not a varbinary?</li>
<li>make sure that there are no white... | https://dba.stackexchange.com |
216,154 | [
"https://dba.stackexchange.com/questions/216154",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/-1/"
] | I can easily raise user defined errors where severity is not higher than 18. When is higher, I get this error
<blockquote>
Error severity levels greater than 18 can only be specified by members of the
sysadmin role, using the WITH LOG option.
</blockquote>
I have access to sysadmin role, so can someone specify t... | <code>WITH</code> is an optional clause that goes at the end of the <code>RAISERROR</code>. A few examples:
<pre><code>RAISERROR('Oops', 10, 1)
RAISERROR('Oops', 10, 1) WITH NOWAIT
RAISERROR('Oops', 10, 1) WITH SETERROR
RAISERROR('Oops', 19, 1) -- Fails with "Error severity levels greater than 18..."
RAISERROR('Oops'... | You can also specify the @with_log parameter while using sp_addmessage sproc
<pre><code>sp_addmessage 50001, 19, 'Test Message', @with_log='True'
</code></pre>
| https://dba.stackexchange.com |
307,981 | [
"https://softwareengineering.stackexchange.com/questions/307981",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/90889/"
] | The primary use for Node.JS is of course as a full server stack, and I've used it in that manner to great success.
However, a number of useful, interesting NPM packages deal with things like transpiling a styling language, adding typing information to typeless JavaScript, running JavaScript unit tests, even having a "... | <blockquote>
if I turn on the warnings and notices on these live production websites, they'll be overloaded with them.
</blockquote>
You should always have warnings turned on to the fullest level in development, testing, and QA, but not in production. Actually, if it's a dogfooding application, i.e. an application t... | If warnings and notices are coming from your code, most definitely fix it. From my experience, in 95% it may be benign, but the 5% highlight a real problem that may lead to countless hours spent chasing.
If they are coming from the third-party code that you must use for one reason or the other, you generally don't ha... | https://softwareengineering.stackexchange.com |
14,890 | [
"https://quantumcomputing.stackexchange.com/questions/14890",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/13973/"
] | For quantum states <span class="math-container">$\vert\psi_1\rangle, \vert\psi_2\rangle, \vert\phi\rangle$</span>, is it true that:
<span class="math-container">$$\tag{1}\langle \phi\vert\psi_1\rangle\langle\psi_1\vert\phi\rangle\langle \phi\vert\psi_2\rangle\langle\psi_2\vert\phi\rangle + \langle \phi\vert\psi_2\rangl... | <span class="math-container">$\langle a | b \rangle$</span> is usually a scalar, so you can move such objects around on the left side, and arrive at (assuming all wavefunctions are normalized):
<span class="math-container">\begin{align}
\tag{1}
\langle \phi\vert\psi_1\rangle\langle\psi_1\vert\phi\rangle\langle \phi\v... | This is wrong, just take <span class="math-container">$c_1>0$</span> and <span class="math-container">$c_2<0$</span>.
| https://quantumcomputing.stackexchange.com |
237,790 | [
"https://stats.stackexchange.com/questions/237790",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/127041/"
] | I found somewhere that test set must not be used as a validation set. Why?
Validation set is acted upon when the model parameters are fixed, and learning happens only through backprop on the training batch.
So, why can't I use test data as validation data?
| I presume you're already understand why performance on the training set isn't representative of the actual performance of the trained model: overfitting. The parameters you learn during training are optimized to the training set. If you're not careful, you can over-optimize the parameters, leading to a model that's rea... | I will stick to neural networks. Note that some people swap validation and test set around.
In neural nets you train until your performance on the validation set starts getting worse ('stopped training'). Therefore the weights are being influenced by the validation set (just not through backprop).
Now you test your... | https://stats.stackexchange.com |
5,513 | [
"https://mechanics.stackexchange.com/questions/5513",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2427/"
] | The struts/pistons are no longer strong enough to hold the boot (trunk for americans) open. I went to buy one from the shop only to find the price was for an idividual unit. Is there ever a case where only one would need to be replaced? - how can I test which one needs replacing if this is the case?
| <pre><code>Is there ever a case where only one would need to be replaced?
</code></pre>
Sure: rust will kill anything but it does tend to start at a point of entry and spread. It could kill one strut before it dissolves the rest of the car. Likewise, a side or corner impact could bend a single strut.
<pre><code>how... | It has been my experience that the gas struts are similar to headlights. Occasionally one will fail early, but most of the time the second unit fails shortly after the first. If only one side is replaced it will take the load of the weaker side. This causes it to wear prematurely as it is carrying more than half the lo... | https://mechanics.stackexchange.com |
147,045 | [
"https://dba.stackexchange.com/questions/147045",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/103607/"
] | I need to modify a procedure to make <strong>statistics</strong> on my database.
I got a temporary table which contains all the data that I need to make those statistics.<br>
It contains all the relevant actions <em>FormIdNb</em> of the working units <em>NumCavalier</em> in one day :
<pre><code>-- Every action from... | Agree with Scott Hodgin, you essentially want to consider <em>MAX(FormIdNb)</em> instead of just <em>FormIdNb</em>, and count the results based on whether the MAX result is greater than, equal to or less than 3.
Adding a correlated subquery to the joining condition, as Scott is suggesting, would be one way.
Another w... | Perhaps, I'm missing something, but it sounds like to want the max(formidnb) for each NumCavalier in the time slice you're processing. I haven't fully syntax checked this, but I think you could add the following to just above your semicolon
<pre><code>AND d.FormIdNb =
(
select MAX(FormIdNb)
FROM #tmp_DailyMissions
... | https://dba.stackexchange.com |
190,530 | [
"https://mathoverflow.net/questions/190530",
"https://mathoverflow.net",
"https://mathoverflow.net/users/63877/"
] | Is there an elliptic curve over $\mathbb{C}[t, t^{-1}]$ that has a nonconstant $j$-invariant? What is an equation for such a curve, if it exists?
| Let me give an analytic argument, to complement Noam's algebraic one. Suppose $E\to \mathbb{C}^*$ is an elliptic curve. Then pulling back $E$ along the universal covering map (also known as the exponential map) $\mathbb{C}\to \mathbb{C}^*$, one obtains an elliptic curve $\tilde E\to \mathbb{C}$. Choosing a basis for... | There is no such curve.
One way to see this is via the action of
${\rm Gal}\bigl(\overline{{\mathbb C}(t)}\big/{\mathbb C}(t)\bigr)$
on the group $E[p]$ of $p$-torsion points of a putative elliptic curve
$E / {\mathbb C}(t)$ that has good reduction at all $t \neq 0, \infty$.
The image of Galois would be abelian, becau... | https://mathoverflow.net |
1,013,915 | [
"https://math.stackexchange.com/questions/1013915",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/68016/"
] | I've just started learning mathematical logic, and my teacher teaches in a very formal and unintuitive way.
I'd like to know what meaning hides behind the symbols below:
For an assignment $\sigma: Terms \rightarrow|M|$ (where M is a structure) we define:
<ul>
<li>$\sigma[x/a](x) = a$</li>
<li>$\sigma[x/a](y) = \sigm... | No, intuitively $\sigma[x/a](x)$ is the function that's exactly the same as $\sigma$ except it maps $x$ to $a$ instead of whatever $\sigma$ maps $x$ to.
| We have to "calculate" the truth value of :
<blockquote>
$(∀x)(∃x)(x < x)$
</blockquote>
using the <em>truth conditions</em> :
<blockquote>
$[∀x\varphi](\sigma) = 1$, if $[\varphi](\sigma[x/a]) = 1$, for all $a$
</blockquote>
and
<blockquote>
$[∃x\varphi](\sigma) = 1$, if $[\varphi](\sigma[x/a]) = 1$, for... | https://math.stackexchange.com |
6,691 | [
"https://dba.stackexchange.com/questions/6691",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/2038/"
] | I have a SQL Server sandbox installation on my local computer. I have set the memory SQL Server instance can use to 1000 mb. When running an intensive operation, memory usage rises up to 1000 mb. When operation is over, SQL Server is still holding the memory. How to free this memory reservation?
| Stop/start the service, nothing else will release the memory back to the OS.
Obviously not something you'd ever want to do with an operational server but perfectly reasonable for a local sandbox. With 3 different instances on my laptop, its the only viable way.
Edit following @Nick's comment.
<blockquote>
As James... | It will give up the memory it is not using automatically as other apps try to commit it.
| https://dba.stackexchange.com |
264,851 | [
"https://stats.stackexchange.com/questions/264851",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/116195/"
] | Say I have the classic mediation scenario, with predictor X, potential mediator M, and outcome Y. My thought to test whether mediation is present would be to do the following:
Set up one structural equation model with only the direct effect of X on M (i.e., setting the mediating coefficients from X to M and M to Y equ... | I don't think it makes sense, because this is a 2 df test, and you're only interested in testing one parameter - that is the mediated effect.
The mediation effect is equal to (X to M) * (M to Y). If that is equal to zero, in the population, then you don't have mediation. This parameter will be zero if either (X to M) ... | I would offer a different perspective: I believe ML estimation CAN be used to test for mediation. This is a trick I thought of which gets Sobel's test statistic from a linear model. The trick is the following: suppose you have a dataset with an outcome Y, an exposure of interest X, and a mediating variable M. These var... | https://stats.stackexchange.com |
437,883 | [
"https://physics.stackexchange.com/questions/437883",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | So I am studying Special Relativity and basic tensor calculus and got stuck at an exercise.
<span class="math-container">$$F^{\mu \nu}: = \left[ \begin {array}{cccc} 0&-{\it E_x}&-{\it E_y}&-{\it E_z}
\\ {\it E_x}&0&-c{\it B_z}&c{\it B_y}
\\ {\it E_y}&c{\it B_z}&0&-{\it cB_x}
\\ {\it... | You are summing matrices in your expression. If <span class="math-container">$A$</span> and <span class="math-container">$B$</span> are matrices, so is <span class="math-container">$A+B$</span>. Each element <span class="math-container">$F^{\mu\rho}g_{\rho\nu}$</span> is a matix itself. For any given <span class="math-... | <blockquote>
Now from here I recognize this to be a dot product between <span class="math-container">$F$</span> and <span class="math-container">$g$</span>.
</blockquote>
It is very difficult to write an answer without knowing your
mathematical background. In my opinion those who answered before me approached the di... | https://physics.stackexchange.com |
20,693 | [
"https://earthscience.stackexchange.com/questions/20693",
"https://earthscience.stackexchange.com",
"https://earthscience.stackexchange.com/users/-1/"
] | I am doing soil related calculations for moisture content and the soil characteristics I need (among others) is the content of the soil as a percentage for:
<ul>
<li>sand</li>
<li>clay</li>
<li>organic matter</li>
</ul>
I am thinking I take the the sand content (in g) divide by 1000 to get sand percentage content and l... | Many tree species do grow faster in climates that are warmer than their native range, especially where the added heat is combined with moist conditions, and faster growth is generally associated with lower density wood. This is why a lot of New Zealand's plantation pine is only good for paper pulp, the warmer wetter cl... | Nothing to do with climate change . Faster growth produces somewhat lower density and strength. There are strength tables for wood written more than 50 years ago that have separate listings for "new " growth and "old" growth. "New " growth being trees growing faster in clear cut areas with... | https://earthscience.stackexchange.com |
15,544 | [
"https://ai.stackexchange.com/questions/15544",
"https://ai.stackexchange.com",
"https://ai.stackexchange.com/users/23527/"
] | Let's assume we have an ANN which takes a vector <span class="math-container">$x\in R^D$</span>, representing an image, and classifies it over two classes. The output is a vector of probabilities <span class="math-container">$N(x)=(p(x\in C_1), p(x\in C_2))^T$</span> and we pick <span class="math-container">$C_1$</span... | writing here my suggestion, because i haven't earned the right to comment yet.
Your main "problem" could be your loss function. It converges, this is why your loss value is decreasing. So I suggest to let it maybe train longer.
Alternatively you could change the loss function to fit your need. For example you could u... | I'm still working on how to make the code work for text generation, but the following converges and work for text classification:
<pre><code>import tensorflow as tf;
tf.reset_default_graph();
#data
'''
t0 t1 t2
british gray is => cat (y=0)
0 1 2
white samoyed is => dog (y=1)
3 4... | https://ai.stackexchange.com |
227,289 | [
"https://mathoverflow.net/questions/227289",
"https://mathoverflow.net",
"https://mathoverflow.net/users/29992/"
] | Suppose that $C\subset \mathbb P^2$ is a plane projective curve (base field is $\mathbb C$) and $C^*\subset (\mathbb P^2)^*$ is its dual. What are the known examples in which $C$ is projectively (i.e., linearly) isomorphic to $C^*$? Besides the non-degenerate conic, I am aware of the cuspidal cubic. Anything else?
Tha... | I only want to explain Yves's example in details.
Put $\mathbf Z:=\mathbb Z[t,t^{-1}]$, the ring of Laurent polynomials. Let $B$ be a group of matrices
[\begin{pmatrix}
1&P&R\\
0&D&Q\\
0&0&1
\end{pmatrix}
]
where $P$, $Q$ and $R$ belongs to $\mathbf{Z}$, and $D\in\langle t\rangle$. The group $... | In the paper,
S. Thomas, On the concept of "largeness'' in group theory
J. Algebra 322 (2009), no. 12, 4181–4197,
it is shown that your "bi-surjectabilty relation" between finitely generated groups is strictly more complex (in the sense of Borel reducibility) than the isomorphism relation. The proof necessarily give... | https://mathoverflow.net |
3,690,906 | [
"https://math.stackexchange.com/questions/3690906",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/621402/"
] | I am a bit stuck. This is what I have so far and I am not sure how to simplify it further:
<span class="math-container">$${{x^2\over 2} - o(x^4)\over (x - {x^3 \over 6} + o(x^5))(x - {x^2 \over 2} +o(x^3))} $$</span>
How do I proceed further?
| What you did is absolutely correct and i hope that i can start from there <span class="math-container">$$\lim_{x\to o}\frac{1-cosx}{sin(x)ln(1+x)}=\lim_{x\to 0}\frac{\frac{x^2}{2}-\frac{x^4}{24}}{(x-\frac{x^3}{6})(x-\frac{x^2}{2}+\frac{x^3}{3})}$$</span> now take <span class="math-container">$x^2$</span> common in both... | Do some <em>asymptotic analysis</em>, it greatly simplifies things:
<ul>
<li><span class="math-container">$1-\cos x\sim_0 -\dfrac{x^2}2$</span>;</li>
<li><span class="math-container">$\sin x\sim_0 x$</span>, <span class="math-container">$\;\ln(1+x\sim_0x$</span>.</li>
</ul>
<span class="math-container">$$\text{Theref... | https://math.stackexchange.com |
325,734 | [
"https://electronics.stackexchange.com/questions/325734",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/158724/"
] | I have designed an RF based PCB board and for testing purpose I would like to measure the power dissipation through each component.
Someone suggested, by measuring the temperature of each component one can get the power dissipation. Is it a reliable solution ? Are there any other ways to measure that?
| It depends why you want to know.
If you want to verify that your simulations are an accurate representation of your design, then measuring voltages at various nodes would be better.
If you want to establish that none of your components are going to fail too early from over-dissipation, then you want the temperature, ... | At the level of physics, temperature is NOT a good indication of heat
dissipation, because dissimilar metals carrying current do heat pumping
(Peltier effect). If you can ignore that kind of effect (you usually
can) then the problem is just as easy as modeling the thermal conductivity
of all your materials, joints, a... | https://electronics.stackexchange.com |
95,584 | [
"https://physics.stackexchange.com/questions/95584",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | This is a very trivial question, but I can't seem to reason it out, again, as to why charges gather at points and edges.
| I think, on would need a model to understand how it works in principle.
<img src="https://i.stack.imgur.com/B8ewp.jpg" alt="enter image description here">
Let us consider the simplified system represented on the figure. You have two metallic spheres with radii $R_1$ and $R_2$ respectively.
They are linked via a metal... | Let's take for granted that excess charges in conductors gather on the surface. Since this is the case, only the component of force on the electrons parallel to the surface is important. Now imagine a charged, conducting square, and think about the charges near the corners of the square. The net force on such a charge ... | https://physics.stackexchange.com |
12,464 | [
"https://earthscience.stackexchange.com/questions/12464",
"https://earthscience.stackexchange.com",
"https://earthscience.stackexchange.com/users/11264/"
] | A large wildfire has been burning for four days some distance from my town. The air is smoky, but not smokier than yesterday or the day before. General wisdom holds that we should all stay indoors.
As I enjoy my relative safety and indoor accommodations, I wonder why the indoor air is safer than the outdoor air. Even ... | If I understand your question correctly, you are asking why air inside is usually cleaner than air outside, especially if it is smokey.
Smoke is actually not a gas, but solid particles that are suspended. Because of this, the smoke particles fall down, but at a very slow rate due to resistance. When the air is blown ... | If you're in the open air you will be exposed to the full concentration of the pollutants in the air. By being inside, there's a reasonable assumption that the rate of interchange of air between inside a house and outside will be low and that inside there will be a lower concentration of pollutants.
Houses and buildin... | https://earthscience.stackexchange.com |
231,999 | [
"https://security.stackexchange.com/questions/231999",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/235106/"
] | Let's say I access a website called example.com with VPN.
Here's the flow: me → ISP → VPN → example.com
Do typical VPN providers use the same IP address to receive data from ISP and send data to the destination server (example.com)?
If that is the case, can the government identify me, by matching VPN server address ... | <blockquote>
Do typical VPN providers use the same IP address to receive data from ISP and send data to the destination server (example.com)?
</blockquote>
This does not matter much. VPN have a severely limited number of entry and exit points. The protocols used are usually different from normal web traffic (i.e Ope... | When you say government, you are implying a certain level of privileged access. Not sure how much of that you are thinking about such as your computer, local ISP, VPN provider, hosting provider for the website;
Here's some variations, assuming that gov always has control over your local ISP (or can request sufficientl... | https://security.stackexchange.com |
163,487 | [
"https://electronics.stackexchange.com/questions/163487",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/37035/"
] | I have an older NI DAQ (PCI-6251) which comes equip with a bunch of ADC's, two DAC's and a hand full of DIO ports. I need to output a pulse of variable width, amplitude and DC offset which the DAQ can do but once you fall below about 5us pulses the rise and fall times become a considerable amount of the actual pulse. ... | How about a fast SPDT CMOS switch that flips between the two DAC outputs and is controlled by one of the digital pins? This eliminates any issues involved with the DAC settling time as the DACs will provide the high and low levels and the digital pin will control which level is selected.
| It sounds like you may have too much capacitive load on the output? Try using a shorter cable or a higher-impedance buffer amplifier.
| https://electronics.stackexchange.com |
344,807 | [
"https://physics.stackexchange.com/questions/344807",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/162215/"
] | how to find out whether a capacitor with different dielectric media is combination of parallel or series capacitors?
Or how one can determine equipotential line in capacitors with different dielectric media?
| If the two dielectrics are stacked (the electric field between the plates is normal to the interface of the two dielectrics), this is equivalent to two series connected capacitors, one for each dielectric and with the capacitance for each determined by the individual dielectric constant, dielectric thickness (which can... | Probably you know:
<ul>
<li>Parallel configuration: $C_{tot} = C_1 + C_2$.</li>
<li>Serial configuration: $\frac{1}{C_{tot}} = \frac{1}{C_1} + \frac{1}{C_2}$.</li>
<li>Dielectric medium: $C_j \to \epsilon_r \cdot C_j$ for $j=1,2$.</li>
</ul>
Now just replace the $C_j$'s in the first and second formula with $\epsilon_... | https://physics.stackexchange.com |
525,117 | [
"https://physics.stackexchange.com/questions/525117",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/248095/"
] | I would like to know what is the meaning of working with a physical measure that is purely imaginary. What I mean with "purely imaginary" is <span class="math-container">$ Z - Re(Z)$</span> where <span class="math-container">$Z$</span> is a complex number.
Furthermore, nowadays are there any physical measures that had... | <blockquote>
Work is being done on the the atoms in the wall, in contact with the
hands, when we push (hard) on the wall.
</blockquote>
At the macroscopic level the wall is considered a rigid body, and since the wall as a whole is not displaced, no work is done.
On the microscopic level you are doing work pushing... | Friction is a red herring here. You can do work on an object by pushing on it, even if there is no friction.
When you push on a spring, you do work by compressing the spring. The spring deforms (shortens) and the work that you do to deform the spring is stored as potential energy in the spring. The spring pushes back ... | https://physics.stackexchange.com |
21,000 | [
"https://dba.stackexchange.com/questions/21000",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/10178/"
] | Informix 11.70.TC4DE:
<pre><code>CREATE TABLE cluster_tbl
(
fk_id INT,
data CHAR(2048)
);
LOAD FROM "presorted.ld" INSERT INTO cluster_tbl;
CREATE UNIQUE CLUSTER INDEX cl_idx ON cluster_tbl(fk_id);
</code></pre>
{###}
<pre><code>CREATE TABLE noncluster_tbl
(
fk_id INT,
data CHAR(2048)
);
LOAD FROM... | No, there's no magic or hand-waving here. It'd be great if synonyms, say, applied to types, but that is not the case. If you want to make these columns first-class citizens, you'll need to change the table. You can automate this to some degree, though I won't post code to help with this unless you specify what you mean... | No, if you want to alter the column type you're going to have to use an ALTER COLUMN statement. Well, that's not true - you can drop the table and recreate it - but ALTER COLUMN is clearly superior :)
| https://dba.stackexchange.com |
1,301 | [
"https://mechanics.stackexchange.com/questions/1301",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/770/"
] | We own a Nissan 350 Z and this morning it would not start. It would turn over but it wouldn't fire. After pulsing the gas a little bit it would start but then letting off the gas would cause it to die. I held it down long enough to get it to stay started. After that I had no issue starting it and assumed I got some bad... | The Check Engine code could be related to the other two. Pull it and see. It might give additional clues to the cause. Attack this issue first.
The traction control and SLIP sound related to each other. Look into what causes the SLIP light to stay on.
Bad fuel typically should not keep the car from accelerating if... | I believe there is a procedure to deciper OBD faults on the VQ35DE motor without any additional hardware - this allows you to count the # of times the CEL blinks to determine a wide variety of fault codes. I'll try to post it when i find it.
Also, there are inexpensive OBD2 bluetooth dongles that will let you pull f... | https://mechanics.stackexchange.com |
208,605 | [
"https://softwareengineering.stackexchange.com/questions/208605",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/52871/"
] | In most programming languages, variables do not have identifying characters like they do in PHP. In PHP you must prefix a variable with the <code>$</code> character.
Example;
<pre><code> var $foo = "something";
echo $foo;
</code></pre>
I'm developing a new scripting language for a business application, and my targe... | The actual technical possibilites and limitations are nothing of the sort as are suggested throughout this thread. Let's clear out those first.
Here's what $ is making possible in PHP:
<ul>
<li>Variable variables</li>
<li>Variables with keyword name e.g. <code>$return</code> or being able to use same name for a varia... | Sigils actually make a lot more sense in perl, where they provide a certain amount of type checking. In php they don't help much outside of templating. You can get a sense of their usefulness and readability by looking around at different languages. Hardly any use them.
In an end user targeted language I'm working ... | https://softwareengineering.stackexchange.com |
2,935,784 | [
"https://math.stackexchange.com/questions/2935784",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/555241/"
] | I want to prove that <span class="math-container">$$\sum_{n=1}^{\infty}\frac{(-1)^{n+1}}{n^{2}}=\frac{\pi^{2}}{12}, $$</span>
using the Fourier Series for the <span class="math-container">$2\pi$</span>-periodic function <span class="math-container">$f(\theta)=\theta^{2},\quad (-\pi<0<\pi)$</span>, that is,
<spa... | <span class="math-container">$$\sum_{n=1}^{\infty}\frac{(-1)^{n}\cos(n\theta)}{n^{2}}=\frac{\theta^{2}}{4}-\frac{\pi^{2}}{12}$$</span>
Take <span class="math-container">$\theta=0$</span> so <span class="math-container">$\cos n \theta = 1$</span>
<span class="math-container">$$
\sum_{n=1}^{\infty}\frac{(-1)^{n}}{n^{2}... | Split it!
<span class="math-container">$$\sum_{n=1}^{\infty}\frac{(-1)^{n+1}}{n^{2}}=\sum_{n ~\text{odd}}\frac{1}{n^{2}} - \sum_{n ~\text{even}}\frac{1}{n^{2}}.$$</span>
Add and subtract the "even" part:
<span class="math-container">$$\sum_{n=1}^{\infty}\frac{(-1)^{n+1}}{n^{2}}=\left(\sum_{n ~\text{odd}}\frac{1}{n^{2... | https://math.stackexchange.com |
198,810 | [
"https://mathoverflow.net/questions/198810",
"https://mathoverflow.net",
"https://mathoverflow.net/users/41075/"
] | Let $F(M,k)=\{(x_1,\cdots,x_k)\mid x_1\cdots,x_k\in M,x_i\neq x_j, \text{ for } i\neq j \}$. It is known that $F(\mathbb{R}^\infty,k)$ is contractible for each $k$.
My question: is $F(S^\infty,k)$ contractible for each $k$? For what kind of space $X$ can we have $F(X,k)$ is contractible for each $k$?
| The space $S^\infty$ is actually homeomorphic to $\mathbb{R}^\infty$. To see this, put
\begin{align*}
B_n &= \{x\in\mathbb{R}^\infty\::\: \|x\|\leq n, x_k = 0\text{ for } k \geq n\} \\
C_n &= \{x\in S^\infty\::\: x_n \leq 1/2,\; , x_k = 0\text{ for } k > n\}.
\end{align*}
Then $\mathbb{R}^\infty$ is the ... | I believe each of these arguments will work.
<strong>Argument 1:</strong> Consider $S^n \subset \Bbb R^{n+1} \subset S^{n+1}$, where the last inclusion is
given by the upper hemisphere (which is homeomorphic to $\Bbb R^{n+1}$. This gives rise to a string of inclusions
$$
\cdots \subset F(S^n,k) \subset F( \Bbb R^{n+1... | https://mathoverflow.net |
2,864,034 | [
"https://math.stackexchange.com/questions/2864034",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/579836/"
] | I am trying to write a simple algorithm given below in mathematical notation. I wrote the formula up to a certain point, but I have no idea of restrictions. For example, I used the NULL statement even though it was not "else". It also needs a "break" statement or equivalent.
<pre><code> var thr = 0.5;
var M = 1... | The idea here is that $T$ is equal to $i$, where $i$ is the first index in the loop for which $\verb|sum|\,/M \ge \verb|thr|$. This can be written in a formula as follows:
$$
T = \begin{cases}0 &\tfrac1M\textstyle\sum_{j=0}^Gj<\verb|thr|\\\min\{i\mid i\in \{0,1,\dots,G\},\tfrac1M\textstyle\sum_{j=0}^ij\ge \verb|... | You need to think about what the code is doing, not just translate the code. Wehn you write $$sum = \sum_{j=0}^{i}i$$
there is a small error that the iteration variable is $j$ so you should write
$$sum = \sum_{j=0}^{i}j$$
More importantly, $sum$ is changing through the computation, so it would be better to write $$su... | https://math.stackexchange.com |
811,884 | [
"https://math.stackexchange.com/questions/811884",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/137446/"
] | The question is as follows:
If $\dfrac{\log_ba}{\log_ca}=\dfrac{19}{99}$ then $\dfrac{b}{c}=c^k$. Compute $k$.
| First we convert all of the logarithms to base $10$ (the base doesnt matter, they just should all be in the same base.) Then we cancel out the $\log a$ on the top and bottom and simplify the expression.
$$\large\frac{\log_ba}{\log_ca}=\frac{\frac{\log a}{\log b}}{\frac{\log a}{\log c}}=\frac{\frac{1}{\log b}}{\frac{1}... | Since $\log_p q =\dfrac{1}{\log_q p}$, we get
$$
\frac{19}{99}=\frac{\log_ba}{\log_ca}=\frac{\log_a c}{\log_a b} = \log_b c,
$$
so
$$
b^{19/99} = c.
$$
Hence
$$
c^{99/19} = b,
$$
so
$$
c^{80/19} = \frac b c.
$$
| https://math.stackexchange.com |
164,045 | [
"https://electronics.stackexchange.com/questions/164045",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/71925/"
] | This is an image demonstrating the use of a pull up resistor.
<img src="https://i.stack.imgur.com/j6Ytc.gif" alt="enter image description here">
I've just started studying electronics and have been learning about ohm's law. Ohm's law says that current within a circuit is equal to the potential drop across that circui... | <blockquote>
I am confused about how pressing the switch actually changes the current being delivered to the [74HC04].
</blockquote>
The 74HC04 has a high-impedance input. It will source or sink only miniscule currents, whether the input voltage is high or low (possibly it will sink more current at some in-between v... | With a 74HC04, the input current is less than 1 uA. With the switch open, the chip current produces a voltage drop of 1 uA x 10k, or about .01 volts, and the voltage at the chip is essentially Vcc. With the switch closed, the voltage into the chip is 0 volts, since the input is now connected to ground. Regardless of th... | https://electronics.stackexchange.com |
4,978 | [
"https://mechanics.stackexchange.com/questions/4978",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2336/"
] | I've got a 2001 WJ 4.0, The right brake light wasn't working, so I installed a new bulb, but I must have done something in the process because now all my brake lights work but I have no running lights. My dash lights all work, and I can't find any blown fuses.
Edit:Brake lights, turn signals, and reverse lights all wo... | Its fairly common for these to burn out sockets for the bulbs, and even often on both sides at the same time. The socket can be removed asa separate piece, and it is fairly likely melted and/or burned
| If the tail lights were hot during the swap you may have broken the filiments. Bumping a bulb that is on or been on recently can cause the filiments to fail. Remove the bulbs hold them up to a light and see if the filimant is intact.
| https://mechanics.stackexchange.com |
319,839 | [
"https://physics.stackexchange.com/questions/319839",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/96810/"
] | I'm a mathematics student currently tackling differential equations, but I'm not very good at interpreting problems so I hope you can help me with this one. I don't really know if the problem is actually a "real simplified" physical model but I thought this was the place to ask.
<blockquote>
<strong>Problem:<... | You can think it like this: the earth-rock system is very similar to a spring-ball system if you ignore any pertubations i.e. wind resistance and Coriolis effect, and the centre of the earth corresponds to the origin of spring.
The force of gravity is
$$F=G\frac{Mm}{r^2}$$
and earth mass $M$ is
$$M=\frac{4}{3}\pi \rho... | I think you are worrying too much it is in simple hormonic motion (SHM) hence the velocity is maximum and acceleration is zero as the equation of gravity at depth of $d$ is given by $g'=g(1-\frac{d}{R})$ where $g'$ is new gravity and R is radius of the Earth hence at center the gravity is zero but you have derived it u... | https://physics.stackexchange.com |
357,979 | [
"https://physics.stackexchange.com/questions/357979",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/169585/"
] | Suppose that I enclose a barometer inside an airtight (but not vacuum) box. Will the pressure reading change?
| We generally choose to use the location of the sun as our origin. You're correct in identifying this is at the focus of the ellipse. We then choose to take quantities relative to the Sun as origin. e.g. the radial distance for an ellipse from a focus is given by
$$
r=\frac{a(1-e^2)}{1\pm e\cos\theta},
$$
whereas to ... | The point in space you define as being the origin cannot change the nature of the force since nature does not care about coordinate systems.
When we say that a central force satisfy
$$\vec F=F(r)\hat r,$$
we are defining the origin as the center of force. However we can consider the center of force at position $\vec r... | https://physics.stackexchange.com |
3,372 | [
"https://scicomp.stackexchange.com/questions/3372",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/1184/"
] | I implemented downhill simplex simulated annealing algorithm. Algorithm is very hard to tune, w.r.t. parameters including cooling schedule, starting temperature...
My first question is about convergence. In general, independently from choice of initial parameters, is it sure that algorithm converges to global optimal... | There is a theorem that syas that a black box algorithm is guaranteed to find the global minimum of an arbitrary smooth (i.e., twice continuously differentiable) function if and only if it samples points densely in the search space.
Here dense is meant in the topological sense, i.e., it must sample points in arbirari... | No, it is not. Very few methods are provably convergent for nonconvex optimization problems. If you're looking for such a method, you might look into branch-and-bound methods.
| https://scicomp.stackexchange.com |
330,914 | [
"https://softwareengineering.stackexchange.com/questions/330914",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/228017/"
] | I am working with EntityFramework 6 code first approach and SQL Server 2014 Express. However, the DBMS may change in future.
That setup allows easily to create a database and add some dummy data for unit tests. Currently, I am creating one database per unit test and drop it after the unit test finished.
I am not sure... | The first thing to note is that, if you are creating and dropping DBs as part of your tests, then they aren't unit tests; they're better described as integration tests.
Pedantic point aside, then the key question is, does each test create a different DB, thus can the tests be run in parallel? Or could two tests runnin... | It is going to be slow, this is the major disadvantage. It might not be a problem if you have a dozen tests, but when you have hundreds it might be a real problem.
| https://softwareengineering.stackexchange.com |
68,642 | [
"https://physics.stackexchange.com/questions/68642",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/26048/"
] | I have a U- like pipe. Its inlet has atmospheric pressure $p_o=10^{5} \, Pa$. Vacuum is applied to the other end with a pressure gradient $\nabla p_v=-30 \cdot 10^{3} \, kPa/s$.
The total time of the simulation is $t=0.25$ s.
I assume that the highest velocity would be reached at the end of the simulation.
After 0.25... | I never particularly liked the textbook description of this topic.
The key concept is that there's a quantity called "energy" that we've decided is useful and can't be created or destroyed$^1$, it can just change "types". This is useful because if you choose a system you want to study carefully, you can learn a lot ab... | first of all you should understand that energy is a number we calculate and then we let nature do her tricks .after this we calculate this number again and find that it is the same number.in case of gravity we can extract the energy back from the gravitational field.but in case of friction this is not possible .energy ... | https://physics.stackexchange.com |
24,870 | [
"https://engineering.stackexchange.com/questions/24870",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/6993/"
] | Why is it that, at least in Ontario Canada, camber diagrams are required for detailed design drawings (Not shop drawings) for bridges with steel girders, but are not required for CPCI Girders?
My understanding is that the camber drawing is required for the steel manufacture to put in a vertical curved to the beam so t... | CPCI girders are prestressed precast concrete girders, right? (Every region seems to have their own acronym for these things so it's not the name I'm familiar with but the mechanics should be the same.)
The short version of the answer is that the prestressing will usually give you the appropriate amount of precamber e... | It might have something to do with the issue of quality assurance.
Steel beams are highly uniform, both in dimensions and material properties. Therefore, if you calculate the deflection of a steel structure and get 2 mm at midspan under dead load, you'll likely get something very close to 2 mm in the real wo... | https://engineering.stackexchange.com |
295,764 | [
"https://mathoverflow.net/questions/295764",
"https://mathoverflow.net",
"https://mathoverflow.net/users/16107/"
] | Apologies if this question is a bit simplistic/vague for MO:
I'm looking for an all-purpose definition in the literature of when a sufficiently generic filter "canonically codes" a generic real. Examples of what I mean come from everyone's favorite notions of forcing to add certain reals "on purpose":
In Cohen forcin... | In the examples that you gave, the question whether you take a "union of stems" or "intersection of conditions" is really just a matter of notation.
For example, there are several ways to define conditions in Silver forcing: as partial functions from $\omega$ to $2$ with coinfinite domains, or as sufficiently unifor... | Restricting to proper notions of forcing, we have the following (occasionally convenient) characterization of when $\mathbb{P}$ adds a new real,
<strong>Proposition:</strong> Assume $\mathbb{P}$ is a proper notion of forcing. Then, $\mathbb{P}$ adds a new real, <strong><em>if and only if</em></strong>,
for every cou... | https://mathoverflow.net |
162,073 | [
"https://softwareengineering.stackexchange.com/questions/162073",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/39814/"
] | What is the process for leaving a company (or even a group/division) in terms of code support?
Is it best to handle all questions? Do you give the remaining developers access to yourself as a future resource? If so, is there a way to not give full access?
I've experienced first hand where answers about the general so... | <blockquote>
How do you support your code post employment end?
</blockquote>
You don't. That's why it's called the <em>end</em>.
If they'd be surprised to see you walk through the door and start using their equipment a month after you left, you should be surprised to have them call you up and ask a bunch of questio... | Normally you prepare for this about 2 weeks before your scheduled end date. Plan some time for a knowledge transfer to another member of the team and try to make sure that they <em>can</em> support the code <em>before</em> you've packed up your desk. Don't set yourself up to be on perpetual support by putting your cont... | https://softwareengineering.stackexchange.com |
588,257 | [
"https://electronics.stackexchange.com/questions/588257",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/289681/"
] | I'm creating a board using an ATSAMS70 microcontroller, and found out in the datasheet that the I2S data out pin (which I'll be using) was multiplexed with another pin I wanna use, which is the SD card interface data 0 pin. I'm familiar with the concept of multiplexing, but I don't really understand how the MCU handles... | <blockquote>
Will it switch very fast at something like twice the peripherals's speed to swap the pin function everytime and let each peripheral do its stuff ?
</blockquote>
No. One of the functions is connected to the pin at a given time. You get to decide which one. You can switch back and forth between them, but it'... | You did not get the concept of multiplexing quit right. Think of it as 'custom' routing within the IC itself. You can decide what function to use on which pins during runtime. Sure, you can switch very fast too - but where is the point of having an ADC and an SD card on the same lanes? I guess your data flow looks like... | https://electronics.stackexchange.com |
2,264,731 | [
"https://math.stackexchange.com/questions/2264731",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/353484/"
] | I'm studying for my Discrete Math final and the following problem with a solution is provided but I'm getting stuck halfway through the solution. Particularly at the step where "we can use the convolution rule to find the coefficients of the product."
Find the infinite series given by the following generating function... | I've figured it out. It was listed in my book as the product rule. I'll add my solution for anyone else who stumbles on this.
The product rule is as follows:
For two functions
$$ A(x) = \sum_{n=0}^\infty a_nx^n $$
$$ B(x) = \sum_{n=0}^\infty b_nx^n $$
Then
$$ [x^n](A(x)*B(x)) = a_0b_n + a_1b_{n-1} a_2b_{n-2} + ... + ... | In this case I would write out the summation and manipulate as follows
$$\begin{align}(15x^2-11x-14)(1-x^2)^{-1}&=(15x^2-11x-14)\sum_{k\ge 0}x^{2k}\\[1ex]
&=\sum_{k\ge 1}15x^{2k}-\sum_{k\ge 0}11x^{2k+1}-\sum_{k\ge 0}14x^{2k}\\[1ex]
&=-14+\sum_{k\ge 1} (15-14)x^{2k}-\sum_{k\ge 0}11x^{2k+1}\\[1ex]
&=-14+... | https://math.stackexchange.com |
148,528 | [
"https://dba.stackexchange.com/questions/148528",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/8419/"
] | I have experienced a problem with flashback and the solution is to recreate the control file (the error was ORA-01207).
So to do this I tried
<pre><code> alter database backup controlfile to trace as '/tmp/trace.sql';
</code></pre>
This creates a file that instructs one to either use set one or set two. i.e. with o... | From /tmp/trace.sql:
<blockquote>
The first set opens the database with the NORESETLOGS option and should be used only if the current versions of all online logs are available. The second set opens the database with the RESETLOGS option and should be used if online logs are unavailable.
</blockquote>
If you're only... | In addition to @Andrew Brennan answer.
The following steps are using RESETLOGS option, assuming online logs are unavailable.
<hr>
Trace the Control File backup
<pre><code>ALTER DATABASE BACKUP CONTROLFILE TO TRACE as 'path\trace.sql'
</code></pre>
Restart the database in NOMOUNT stage
<pre><code>SHUTDOWN IMMEDIATE... | https://dba.stackexchange.com |
174,556 | [
"https://electronics.stackexchange.com/questions/174556",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/73531/"
] | I am trying to convert 5V to a constant current source
<img src="https://sub.allaboutcircuits.com/images/03039.png" alt="circuit">
for op amp I use AD822.
for 250 ohm I use 180 ohm, so I should get a current of 28 mA.
I verified when Rload = 0, 28 mA across negative terminal to ground.
But when I put Rload to circui... | Have you tried bog standard thermal glue? They are not particularly strong, and the component can be slid with modest force to release from adhesion. The glue can be scraped off fairly easily, I don't know what solvent would remove it, but I can't imagine it would be easy to find one that does it. An alternative idea w... | I've used Kapton tape in the past for larger ICs that I need to keep down. Smaller ICs can be addressed by placing a small amount of solder paste on a corner pad. Place part and REflowing that corner pin. Very Small shifts can then be made to part before soldering the other corners then rest of pins.
| https://electronics.stackexchange.com |
18,054 | [
"https://mathoverflow.net/questions/18054",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2389/"
] | Hello all, the $\Delta$ operator on functions $\mathcal{N} \to \mathbb{R}$
(where $\mathcal N$ denotes $\lbrace 1,2, \ldots , \rbrace$ )defined by
$\Delta(f)(n)=f(n+1)-f(n)$ is well-known and
it is not very hard to show by induction that
$f$ is a polynomial of degree $\leq k$ iff $\Delta^{k+1}(f)$ is identically zero... | One can also get this from a standard form of the remainder in Taylor's theorem. Namely, if $k>\lambda$, and $T_{k-1}(x)$ is the degree $k-1$ Taylor polynomial of $f(x)$ at $x=n$, then
$$f(x) = T_{k-1}(x) + \frac{f^{(k)}(\xi_x)}{k!} (x-n)^k$$
for some $\xi_x \in [n,x]$. Applying $\Delta^k$ kills the Taylor polynom... | There is an "iterated" version of the mean value theorem which states that for
a smooth enough function $f$ on an interval that $\Delta^k f(x)=f^{(k)}(\xi)$
where $\xi$ is between $x$ and $x+k$. This should be enough for your
purposes.
| https://mathoverflow.net |
20,984 | [
"https://electronics.stackexchange.com/questions/20984",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5674/"
] | This is simple mathematical question but I cannot figure it out:
Compact fluorescent lamps consume 75% less wattage and still deliver equal power of incandescent lamp. If 15W compact fluorescent lamp which consumes 75% less wattage, delivers same result as 60W incandescent lamp then how much wattage of incandescent la... | This is off topic, but it's right out of 7th grade arthmetic and easy to answer, so I'll just do it:
<i>If johnny leaves his apples on the table and Suzy always takes 3/4 of them at noon, then how many apples did Johnny start with if Suzy left 9 of them?</i>
F = I - (75% I)<br>
F = 25% I<br>
F = .25 I
I = F / .25<br... | I'll not go into detailed description why this is not a good way to compare the light sources. Basically the only real way to be sure is to read the specification of the 9 W CFL or to do measurements yourself.
Anyway, to answer the question here we have a basic elementary-school lever proportion.
If we assume that bo... | https://electronics.stackexchange.com |
36,356 | [
"https://mechanics.stackexchange.com/questions/36356",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/10053/"
] | So, I've been having trouble starting my 02 - Diesel Excursion 4WD (7.3 PSD with 4R100 tranny). I get the squealing/grinding sound of a starter/flexplate with missing teeth. I replaced the starter last month due to the same issue and could see the flex plate had some worn teeth. This is a common issue on this vehicle.
... | I never use the tool, there's never enough room to get it in there. I use a screw driver/pry bar to turn the flywheel/flexplate by the teeth. You should be able to do that once you get the cover and or starter off. And yes you can turn the flywheel/flexplate by turning the crank bolt. That will work fine to move the fl... | Summit Racing offers a (Performance Tool Flywheel Turners W80510) for under $20. For it to work you have to have a removable cover that allows access to the bottom of the flywheel. I have a similar tool and it works well although it can get tough to turn once the cylinder pressure builds up.
| https://mechanics.stackexchange.com |
131,194 | [
"https://softwareengineering.stackexchange.com/questions/131194",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/33159/"
] | I have a question concerning derivative works of GPL'ed software. Imagine the following situation: A company writes a software (A) using a library (B) which is released under the terms of the GPL. Now of course, software (A) has to be released under a compatible license to the GPL. But what about dual-licensing? If sof... | <blockquote>
Now of course, software (A) has to be released under a compatible
license to the GPL. But what about dual-licensing?
</blockquote>
Software A can be released under any number of licenses as long as they are all compatible GPL.
<blockquote>
If software (A) is released under two licenses, GPL and a ... | If you created a derived work of a lib you received under the GPL then your lib is GPL.
If you paid them for a commercial license then the derived work is under whatever the terms are for that license
| https://softwareengineering.stackexchange.com |
507,810 | [
"https://physics.stackexchange.com/questions/507810",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/227820/"
] | Suppose in a situation there is a man falling from a height, when he falls from a height and touches the ground then he applies some force on the ground which is equal to his weight, and in another situation the same man with same weight is lying down on the ground.
So is it that that the force applied by the man on t... | Answer of both case is different, in first case while the man is in air, he is in free fall with respect to earth, he apply force when he just touches he earth, there will be the impulse experience by the earth due to change in momentum of your body from <span class="math-container">$mv$</span> to <span class="math-con... | No, the force applied in the two cases won't be the same.
The falling person will exert a force on contact to the earth which will be much higher than his weight. The force will be impulsive and is given by
<span class="math-container">$$\vec F=\lim_{\Delta t\to 0}\frac{\Delta \vec p}{\Delta t}$$</span>
That's beca... | https://physics.stackexchange.com |
83,175 | [
"https://mathoverflow.net/questions/83175",
"https://mathoverflow.net",
"https://mathoverflow.net/users/19051/"
] | Periodic matrices in SL(3,Z) will be conjugated to
product of periodic matrices in SL(2,Z) by +- indentity on a third
integer direction. Is this true?
<hr>
Sorry, following your comments, maybe something I said is misleading. I state the original question:
Consider a periodic automorphism $\phi$ on $Z^3$, can we... | ok, let me expand Geoff's suggestion. Let $A\in SL(3,\mathbb{Z})$ be such that $A^n=Id$ for some positive integer $n$. Since the characteristic polynomial of $A$ is a cubic polynomial of the form $-t^3+\cdots +1$, it has a positive real root; and since all roots of $A$ are roots of the unit, 1 is an eigenvalue of $A$. ... | The matrix
$0\ 1\ 0$
$1\ 0\ 0$
$0\ 0 \-1$
in $SL_3(\mathbb Z)$ is not conjugate to any block sum of an $SL_2(\mathbb Z)$ matrix and $+1$. And of course it is not conjugate to any block sum of an $SL_2(\mathbb Z)$ matrix and $-1$, either.
For $GL_3$ and $GL_2$ the answer is yes.
EDIT This last statement is wrong;... | https://mathoverflow.net |
2,897,474 | [
"https://math.stackexchange.com/questions/2897474",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/582814/"
] | I was reading complex numbers when I came across this inequality:
<blockquote>
$- \pi ≤ arg(z) ≤ \pi$
</blockquote>
Where $z$ is a complex number, I want to know what this inequality mean?
Can't it simply be that,
<blockquote>
$0 ≤ arg(z) ≤ 2 \pi$
</blockquote>
| As mentioned in the comments, the $1 \over 12$ answer is wrong by both interpretations of "two doublets". What leads to this "answer" is the flawed reasoning that:
$$P_{\,{\rm 2-doublets}} = \eqalign{
{\rm (*\,aabb\,*)\;} &(1) (1/6) (1) (1/6)\; + \cr
{\rm (*\,abab\,*)\;} &(1) (1) (1/6) (1/6)\; + \cr
{\rm (*\,a... | Using the counting principle, I get the same answer as the question contributor:
$6+5+4+3+2+1=21$ different pairings of doubles which includes $6$ identical pairs.
There are $\frac{4!}{2!2!}= 6$ ways to get each pairing of different doubles
Hence $P = \frac{15\cdot \frac{4!}{2!2!}+6}{6^4} = \frac{2}{27}$
| https://math.stackexchange.com |
200,533 | [
"https://security.stackexchange.com/questions/200533",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/195605/"
] | I want to implement the following encryption scheme. The data is created and stored on a web server, but related to some user of the system (i.e. it is entered "on behalf" of the user). Both encryption and decryption process should involve a request to a mobile device of this user (the encryption password is located on... | Before designing a protocol, we need to make an important decision: <strong>do we trust the server?</strong>
If we do, the design can be quite simple: HTTPS would be used for communication encryption, and disk encryption would be used for data encryption, and there would be no encryption in application code. All acces... | <strong>EDITED because of misunderstanding</strong>
In my opinion, the mechanism described isn't good because of several issues:
<ul>
<li>You're (more or less) about to re-invent asymetric encryption... Generally, re-inventing crypto stuff isn't a good idea ;-)</li>
</ul>
For the same needs i would:
<ol>
<li>During... | https://security.stackexchange.com |
253,247 | [
"https://dba.stackexchange.com/questions/253247",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/192202/"
] | I've got to filter data in a string column and thus need to compare the column using <code>NOT LIKE</code> with a bunch of strings.
I'm using SQL Server and my code looks like this:
<pre><code>SELECT history.date,
history.new_value,
res.resource_name
FROM item_history history,
owned_resource ... | I would use join here instead of old writing way<br>
Regarding "lower" are you sure that this is needed?<br>
Did you check collation of new_value?<br>
If it has CI(case insensitive) in collation name it you can avoid using lower.
If you do, you can write something like this
<pre><code>WITH cte
AS ( SELECT history... | For the sake of completeness, you could have solved the problem (many excludes) on the following way too:
<pre><code>SELECT history.date
, history.new_value
, res.resource_name
FROM item_history AS history
INNER JOIN owned_resource AS res
ON history.com_par_id = res.own_resource_uuid
AND res... | https://dba.stackexchange.com |
130,571 | [
"https://softwareengineering.stackexchange.com/questions/130571",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/29270/"
] | Why was the property <code>string foo = string.Empty</code> included in the BCL? It seems more verbose and no clearer than just using an empty string (<code>string foo = ""</code>)
| I can only assume here:
<code>string.Empty</code> has been defined for explicitness - when initializing a string, it may not be clear from context that <code>""</code> was indeed explicitly meant as an initializer (instead of <code>null</code> or say <code>" "</code> or just as a place holder during testing). Using <c... | I'm not 100% sure of the sources where I learned these, but some of the points for using it include:
<ul>
<li>Each string in a .NET assembly is unique, so having
<pre><code>string foo = "";
string bar = "";
</code></pre>
results in 2 strings in the output assembly since strings are immutable. Having both reference ... | https://softwareengineering.stackexchange.com |
144,343 | [
"https://electronics.stackexchange.com/questions/144343",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/59831/"
] | I need to pass integer values from one PIC to another through serial port
for char I can use the following code
<pre><code>char data1='a';
TXREG=data1;
while(PIR1.TXIF==0);
</code></pre>
but when I try to pass int type variable it returns an ASCII equivalent..
Is there anyway ... | You already are sending integer values over the UART with the code you show. Your problem is apparently sending integers that are more than 8 bits wide.
The UART inherently only sends 8 bit bytes (in the most common configuration) at a time. If you want to send a wider integer, you have to send more than one byte to... | To send an integer value over the UART you have to send 2 bytes. For example:
<pre><code>int data = 0x1234;
TXREG = data & 0xff;
while(PIR1.TXIF==0);
TXREG = (data >> 8) & 0xff;
while(PIR1.TXIF==0);
</code></pre>
| https://electronics.stackexchange.com |
30,765 | [
"https://mathoverflow.net/questions/30765",
"https://mathoverflow.net",
"https://mathoverflow.net/users/6094/"
] | Is there a notion of an octonion prime?
A Gaussian integer $a + bi$ with $a$ and $b$ nonzero is prime if $a^2 + b^2$ is prime.
A quaternion $a + bi + cj + dk$ is prime iff $a^2 + b^2 +c^2 + d^2$ is prime.
I know there is an eight-square identity that underlies the octonions.
Is there a parallel statement, something lik... | You should probably read "On Quaternions and Octonions" by J.H. Conway and D.A. Smith
P.S. It's "octonion" not "octonian"
Edit: The first thing you will find is a discussion of integral numbers. For the complex numbers you have $\mathbb{Z}[i]$ (aka Gaussian integers) which is an $A_1\times A_1$ lattice. You also have... | There may be Octonion primes as Conway suggests as there are
Hurwitz and Gaussian primes, the great difficulty is that of calculating
and visualizing an eight vector of Integers so that their Norm is
a prime on current desktop computer. Just going 5 deep involves
looking at 5^8 numbers. Projecting the two Gaussian pr... | https://mathoverflow.net |
406,493 | [
"https://physics.stackexchange.com/questions/406493",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/193942/"
] | I have read the quantum mechanical model of an atom which says that path of an electron around the nucleus is uncertain due to uncertainity principle which says that it is impossible to measure both momentum and position of an electron
at the same time so it is impossible for an electron to move in a well defined circu... | <strong>1)</strong>
I would not call this a capacitor. Your typical parallel plate capacitor has two charged plates kept at some potential difference (by being hooked up to opposite terminals of a battery, for example). These are just two charged plates that end up being connected and the charges balance out on each si... | I will answer the questions in order 2-3-4-1.
<hr>
<ol start="2">
<li>Charge – After closing the switch, will there be equal charges on both plates (each $(Q_1+Q_2)/2$) in order to minimise repulsion?</li>
</ol>
Ans– Yes, both plates will gain equal charge which can be seen through symmetry arguements.
<hr>
<ol st... | https://physics.stackexchange.com |
90,760 | [
"https://security.stackexchange.com/questions/90760",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/77664/"
] | Is there any point in signing an OpenPGP public key that has not been uploaded to a key server? In other words: does anyone except person A who signs person B's public key notice that the signing has taken place?
Background: since I haven't decided to upload my public key to a key server yet, I'm wondering if there's... | Web of trust? Instead of using a centralized, public key server, you and your friends could be exchanging key files directly. In which case the added signatures would be doing something.
However, if you are going to sign it, and then leave the file on your hard drive then you are correct that it doesn't do much good t... | <h2>Keeping Certifications Private or Public</h2>
The whole OpenPGP web of trust idea is build around certifications (signatures of other keys) being publicly available, so other users can build trust paths on these. Keeping certifications private is surely legit, but will not help others (also contacting you).
If yo... | https://security.stackexchange.com |
285,197 | [
"https://mathoverflow.net/questions/285197",
"https://mathoverflow.net",
"https://mathoverflow.net/users/398/"
] | Let $0<\sigma\leq 1$. Let $T$ be large. How can we give good explicit $L^2$ bounds on the tails of $\zeta(\sigma+it)$? That is, we want to bound the quantity $$\int_{\sigma-i\infty}^{\sigma-iT} + \int_{\sigma+iT}^{\sigma+i\infty} \frac{|\zeta(s)|^2}{|s|^2} ds.$$
Morally, we should expect something about as good as $... | Let $\sigma>0$ be fixed, and let $T\geq 2$ be a parameter.
By Theorem 4.11 in Titchmarsh: The theory of the Riemann zeta-function,
$$ \zeta(\sigma+it)=\sum_{n\leq T}n^{-\sigma-it}+O(T^{-\sigma}),\qquad T<|t|\leq 2T.$$
It follows that
$$ \int_{\sigma+iT}^{\sigma+2T}|\zeta(s)|^2\,ds\ll T^{1-2\sigma}+\int_T^{2T}\le... | Thanks, GH! Let me have another go. I think the following is the right way to go about things, at least if one wants something self-contained and with good, explicit constants. (The latter more or less implies the former, given that almost all of the literature is non-explicit.)
We want to estimate
$$\frac{1}{2\pi i} ... | https://mathoverflow.net |
244,606 | [
"https://physics.stackexchange.com/questions/244606",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/7424/"
] | The concept in my mind is that an asteroid is on a vector similar to Earth's, but slightly slower (e.g., 50kmh slower). As Earth passes it, it enters the atmosphere at a sharp angle, and since Earth was passing it, it just barely touches down due to Earth's gravity and atmospheric drag.
Given a large asteroid (e.g., 5... | If the asteroid is in parallel to the orbit of the earth and at rest it will feel the gravitational attraction and will fall with velocity growing as $g\cdot t^2.$ This force will be there whatever the angle and velocity of the asteroid, centrifugal forces may make it miss the earth in a parabolic orbit, or be caught i... | Well, technically, the answer is no as the other answers and comments also say.
The approach speed can not be less than escape velocity.
But in order for such a thing to happen, nature has to be really creative and totally in our favor. For example, the asteroid can have a very very lucky combination of these:
<ol>
<... | https://physics.stackexchange.com |
3,165 | [
"https://stats.stackexchange.com/questions/3165",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/253/"
] | Let's say we created a plot, with labels:
<pre><code>plot(1, xlab = "text", ylab = "text times three") # text too small
</code></pre>
In this plot there is still a lot of free region to enlarge the text. We could do so by using cex.lab, like this:
<pre><code>par(cex.lab = 2)
plot(1, xlab = "text", ylab = "text time... | The following uses calls to par(), strheight() and strwidth() to fit within the borders of the plot area and the edges of the margin for the text. They don't rescale together the same so this will give you a framework for redrawing your graph if you change the overall dimensions. If you want something different this ... | I can't think of an answer to Q1, but Q2 can be done via separate calls to <code>title()</code>. Here's an example
<pre><code>x <- 1:10
y <- runif(10)
plot(y ~ x, ann = FALSE)
title(ylab = "my Y axis label", cex.lab = 2)
title(xlab = "my X axis label", cex.lab = 3)
</code></pre>
But I don't see the value in doi... | https://stats.stackexchange.com |
139,333 | [
"https://cs.stackexchange.com/questions/139333",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/135728/"
] | The Problem:
<blockquote>
Say that a language is prefix-closed if all prefixes of every string
in the language are also in the language. Let C be an infinite,
prefix-closed, context-free language. Show that C contains an infinite
regular subset.
</blockquote>
Can we show this by using Myhill-Nerode Theorem?
| Given a normal form grammer <span class="math-container">$G$</span> for an infinite prefix-closed <span class="math-container">$L$</span>, examine the (almost) regular grammer <span class="math-container">$G'$</span> obtained by transforming rules of the form <span class="math-container">$A\rightarrow BC$</span> into <... | Another easy solutions uses the pumping-lemma for context-free languages. Let <span class="math-container">$L$</span> be infinite, prefix closed and context free. Then there is an <span class="math-container">$l$</span> such that for all <span class="math-container">$z\in L$</span> with length at least <span class="mat... | https://cs.stackexchange.com |
1,172,341 | [
"https://math.stackexchange.com/questions/1172341",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/220469/"
] | I'm trying to find the antiderivative of $A(x)=\cos(x)\log(1+\cos(x))$
By using integration by parts I get :
$$\int A(x)\, dx = \sin(x)\ln(1+\cos(x))+\int \frac{\sin^2(x)}{1+\cos(x)} \\ =\sin(x)\ln(1+\cos(x))+\sin(x)\int \frac{\sin(x)}{1+\cos(x)}\\ =\sin(x) \ln(1+\cos(x))+\sin(x)(-\ln(1+\cos x))=0$$
However using ... | On the second line, you cannot pull the $\sin(x)$ in front of the integral. You should use
$$
\sin^2(x)=1-\cos^2(x)=(1+\cos(x))(1-\cos(x)).
$$
| The mistake was the Integration of $\frac{sin^2 (x)}{1+cos(x)}$. Use $sin^2(x)=1-cos^2(x)=(1-cos(x))(1+cos(x))$.
| https://math.stackexchange.com |
45,172 | [
"https://mechanics.stackexchange.com/questions/45172",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/29188/"
] | i am using Honda Shine since 2014, i replaced battery after 2.5 yrs with new exide dry battery, but after a 4-5 month starter, horn, indicator fail to work and then my bike unable to start, i replaced that battery with the new one immediately but same problem occur in next weeks, after 1 week its running like out off ... | Although I can't imagine it would be needed for your application, there is a truly non-hardening thread locking compound available. Vibra-Tite VC-3 is an acrylic polymer that dries to a resilient plastic substance as the solvent evaporates. It will allow the fastener to be re-torqued or even be removed and reused while... | The Loctite brand fastening sealants are Anerobic sealants that cure in the absence of air. That is why they cure when your fastener is assembled and they ask that you wipe away any excess. Whether they are considered Hardening sealants or not I don't know. Any Loctite sealant, including the red, will come undone and y... | https://mechanics.stackexchange.com |
650,168 | [
"https://physics.stackexchange.com/questions/650168",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/306389/"
] | It's a thought experiment which I've been running in my mind for long in order to understand tidal forces. Any suggestions/ideas are appreciated.
Assume a perfectly spherical planet with no atmosphere.<br>The planet is not in a translating motion, but it is rotating.<br>
And we have a stationary rocket with infinite su... | The point is that spins are interacting with each other as well as with the external field. Plus, they get disturbed by the statistical motion of the particles. That is the reason for example, why ferromagnetism breaks down above a certain temperature. Furthermore, due to the Pauli principle, spins tend to pair with re... | Every subatomic particle in atoms has a <strong>magnetic dipole moment</strong>. Generally, these particles pairwise form closed magnetic loops and do not contribute to a magnetic dipole moment of the atom.
Permanent magnets are those in which the remaining <strong>unpaired particles</strong> in the material are more o... | https://physics.stackexchange.com |
376,288 | [
"https://mathoverflow.net/questions/376288",
"https://mathoverflow.net",
"https://mathoverflow.net/users/155247/"
] | If we define <span class="math-container">$$f(n) = \Bigl\{ n \sum_{k=2}^{n-1} \frac{1}{k}\Bigr\}$$</span>
is it true that <span class="math-container">$f(n) \ne f(m)$</span> whenever <span class="math-container">$n \ne m, \forall m,n \in \Bbb{N}$</span> (where the curly braces denote the fractional part)?
I wanted to e... | It follows from Bertrand's postulate that <span class="math-container">$mH_m - nH_n$</span> is an integer only in the case <span class="math-container">$n=m$</span>. Suppose <span class="math-container">$n<m$</span>, and assume that <span class="math-container">$m$</span> is reasonably large below (say <span class=... | Here is a proof that <span class="math-container">$nH_n-mH_m$</span> cannot be an integer for <span class="math-container">$n>m$</span> in the case that <span class="math-container">$n$</span> is odd while <span class="math-container">$m$</span> is even. The argument in that case follows directly from the <A HREF="h... | https://mathoverflow.net |
39,096 | [
"https://electronics.stackexchange.com/questions/39096",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1024/"
] | Firstly some background:
I would like to make a magnetic stirrer, like the ones they use in chemistry labs:
<img src="https://i.stack.imgur.com/i2L70.jpg" alt="Magnetic Stirrer">
A small bar magnet sits inside the glass jar, while another bar magnet, attached to a motor is spun underneath the jar. This causes the fi... | Finally found the closest thing to an answer, thanks to hints from David Kessner and Ignacio Vazquez-Abrams.
A pancake motor (AKA Floppy Drive motor) has a planar separation between the rotor and stator, and so is most suitable for working through a sheet of glass.
<img src="https://i.stack.imgur.com/QfTKd.jpg" alt="... | My college roommate built exactly what you are talking about. This would have been back in 1978-79 or so. It worked quite well, and we used it mainly to mix up our Tang<sup>TM</sup>. IIRC, he didn't use a microprocessor — just a 555-based oscillator and a ring counter to generate the waveforms to drive the coils.... | https://electronics.stackexchange.com |
596,015 | [
"https://electronics.stackexchange.com/questions/596015",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/288611/"
] | Please help with this. I have a generator which I loaded in parallel with other generators. I noticed that the power factor became exactly one and after a while leading.
The other two generators had a power factor of 0.5 about. Can there be a damage to the windings of the generators if I make more attempts to synchroni... | If the generators are connected in parallel but have differing power factors, this is ultimately due to uneven load-sharing between them. The overall power factor depends on the load of course, but generators in parallel won't necessarily share equal parts of the complex/apparent power.
In your case, one generator sou... | There's alot of information missing... it would be great if you add specifics to your question: setup schematic, model numbers, etc.
However, there may be some value in some general information wrt this type of question...
If we're talking three-phase power generation, connected to a bus bar; then a key aspect of ope... | https://electronics.stackexchange.com |
432,253 | [
"https://stats.stackexchange.com/questions/432253",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/263187/"
] | I need to assess the impact of cultures on urban economies. The hypothesis is that more entrepreneurship oriented culture will better facilitate the local economy, controlling for other factors (that may contribute to local economic growth). The study area is 3 cities next to/not far from each other but with different ... | Comparing error to predicted value is frequently done: the result is a relative error. Whether relative or absolute error is more important depends on your data/application/the task at hand.
However, relative errors are most useful if the denominator gives a good impression of what the encountered values are like. I... | It seems that you are relating the value of MAE to the value of mean of the time series? Thats not a good idea imho: if you shift the whole series by a constant, its mean would also shift by that constant, but the MEA / quality of your model should stay the same (if your model is e.g. some regression with intercept, th... | https://stats.stackexchange.com |
116,774 | [
"https://mathoverflow.net/questions/116774",
"https://mathoverflow.net",
"https://mathoverflow.net/users/30082/"
] | In a note I saw this fact that $PSL(3,q)$ where $q=p^n$ does not have any abelian subgroup of order $q^3$. But I could not prove it or find any reference about it, could you please help me about it?
Thanks
| One of the Sylow $p$-subgroups of $PSL(3,q)$ is the subgroup of all unitriangular matrices (i.e. upper triangular matrices with 1 on the diagonal): just compute the order of $PSL(3,q)$ and the order of the unitriangular subgroup which is $q^3$ (or look in Bogopolsky's group theory book). Therefore if $PSL(3,q)$ contain... | I think you can find the answer in the paper "Finite simple groups with some abelian Sylow subgroups" by Rulin Shen.
Best regards
| https://mathoverflow.net |
16,533 | [
"https://physics.stackexchange.com/questions/16533",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5791/"
] | Two plastic sheets with charged densities as shown:
<img src="https://i.stack.imgur.com/DlpDA.jpg" alt="enter image description here">
I'm trying to find the field at $B$. I obtained the correct answer by adding up the fields created by each charge density. But I realized that since the field is uniform in the region... | You tell us that one surface of the box is at $B$, but you're a little vague on where the opposite face is. You do say that your surface is "between the two sheets", so I think you may mean that the surface is entirely contained in the space between the two sheets. The box does not intersect any charged surface. Wit... | If you draw a gaussian box between the plates, the flux in the surface near to $\sigma_3$ is equal to that of the surface $\sigma_2$. In this case $\vec{E}\cdot\vec{A}$ is the same as $\vec{E}\times\vec{A}$.
If you apply the superposition principle and for each separate plate and calculate the field by Gauss law the... | https://physics.stackexchange.com |
448 | [
"https://cardano.stackexchange.com/questions/448",
"https://cardano.stackexchange.com",
"https://cardano.stackexchange.com/users/1092/"
] | I've minted a token but some of the metadata.jsosn properties don't look so great. Is there a way to update them?
The general form I've tried is:
<pre><code>cardano-cli transaction build-raw \
--fee $fee \
--tx-in $txhash#$txix \
--tx-out $address+$output \
--metadata-json-file metadata.... | Technically you cannot change the metadata for a token once its minted. Thats the whole point of putting something on the blockchain-its immutable. On Cardano, token metadata is just metadata in the minting transaction. What you are doing is just adding new metadata to a new transaction with the token. This is not chan... | This seems to work:
<pre><code>export address="address the token was created on"
export txhash="transaction hash the token was create don"
export txix="index of txhash above"
export funds="funds at the txhash"
export policyid="the token policy id"
export fee="0&quo... | https://cardano.stackexchange.com |
85,820 | [
"https://dsp.stackexchange.com/questions/85820",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/65792/"
] | I am new to DSP and I am trying to understand how to work with fixed point operations and in particular the Q31 format.
In floating point (full range) I am doing some multiplications, it could be for example <code>6.0 * 10.0 = 60.0</code>. Converting this to Q31 would require first scaling it down to [-1,1) and then co... | Fixed point processing is very difficult (unless it's a very simple algorithm and well behaved data).
Here is roughly how this can be done. For simplicity I will assume that the fixed point data type is a 32-bit signed integer.
<ol>
<li>Prototype your entire algorithm in floating point. Make sure it's fully unit tested... | OK -- I see your problem. You're multiplying <span class="math-container">$a$</span> and <span class="math-container">$b$</span>, by first bringing them into Q31 then bringing them out. <span class="math-container">$a$</span> and <span class="math-container">$b$</span> happen to be 6 and 10, but let's not worry about... | https://dsp.stackexchange.com |
176,099 | [
"https://dba.stackexchange.com/questions/176099",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/63371/"
] | We are going to migrate our data center from one state to another in next 3 months. I wanted to know, what is the best possible way to migrate one of our biggest database (i.e. ~7TB in size) as quickly as possible. Here is the information on the server and database:
<ul>
<li>Existing Data-Center: Georgia</li>
<li>New ... | One could write a book on this topic, but one option would be an out-of-band initial replication of your database to the new site by flying a copy of the server hard drive(s) to New Jersey, followed by log shipping until you catch up, followed by setting up your "transnational" replication to target both old and new si... | Suggested plan:
(1)Set up the databases at new location and bring the online.
(2)Perform SQL replication between old and new locations.
(3)Bring the new location to production environment.
(4)Bring the old location offline.
| https://dba.stackexchange.com |
263,119 | [
"https://softwareengineering.stackexchange.com/questions/263119",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/156533/"
] | Is possible and, if so, common practice to initialize an object inside a class in Python?
<pre><code>self.field = Class()
</code></pre>
| Everything in Python is an object, so yes, this is common practice. You could not create a meaningful Python program without creating other instances in your own classes.
| If you want to do it in a Object Oriented way, you could pass a factory into the class, so that you can instantiate your class using a factory method:
<pre><code> self.field = myFactory.GetSomeClass()</code></pre>
| https://softwareengineering.stackexchange.com |
72,158 | [
"https://mathoverflow.net/questions/72158",
"https://mathoverflow.net",
"https://mathoverflow.net/users/16969/"
] | Hello everyone,
it seems to be "well-known" that $H^0(X;End(V))$ only contains isomorphisms where $X$ is a Riemann surface and $V$ a stable (algebraic) vector bundle over $X$. The usual proof considers (roughly) the (coherent) image sheaf of a non-zero vector bundle morphism $\varphi:V\to V$ and one obtains a contrad... | Consider the two following potential definitions of stability of a locally free coherent sheaf $E$.
(A) Every subbundle (i.e. locally free subsheaf) has strictly smaller slope.
(B) Every subsheaf has strictly smaller slope.
I claim that over a curve $X$ these two definitions are equivalent. Indeed, suppose (A) ho... | Although this is rather a comment (or at best a partial answer) than an (honest) answer, I don’t write it as such. But it’ll contain some thoughts about my question and so it seems appropriate to write it as an answer (at least to me…).
@Jason Starr: Of course you’re completely right. Sorry, I was probably too sloppy... | https://mathoverflow.net |
124,830 | [
"https://cs.stackexchange.com/questions/124830",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/104656/"
] | I am trying to prove the fact that every CFL is decidable, however I can't come to terms with what the statement exactly means.
I know that generation of a particular string by a given CFG is a decidable problem. This means that we can design a TM that will definitely halt and tell us whether the given string is gener... | The phrase
<blockquote>
Every context-free language is decidable
</blockquote>
has the following meaning:
<blockquote>
If the language <span class="math-container">$L$</span> is context-free, then <span class="math-container">$L$</span> is decidable
</blockquote>
or in other words
<blockquote>
If <span class... | It means for every context free language there is an algorithm that can correctly decide if any string S is in the language or not.
We can actually say something a lot stronger: There is actually a known algorithm that can take an arbitrary context free language and a string as input and decide in polynomial time whe... | https://cs.stackexchange.com |
221,086 | [
"https://physics.stackexchange.com/questions/221086",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/94537/"
] | A long solenoid has current $I$ flowing through it, also denote $N$ as the turns per unit length. Take its axis to be the $z$-axis, by symmetry the only component of the magnetic field inside is $B_z$. Find the magnetic field at the center of the solenoid (on the axis). Also, find the magnetic field at the ends of the ... | Notice, the magnetic field at some internal point on the axis of a solenoid is given by general expression
$$B=\frac{\mu_0 NI}{2}(\cos\theta_1-\cos\theta_2)$$
where, $\theta_1$ & $\theta_2$ are the angles between axis & the lines joining the extreme-points of both the ends of solenoid to the concerned point. ... | since you are concerned about a <em>long</em> solenoid, this problem has a very simple solution.
Suppose you have two identical long solenoids, each of them having magnetic field $B$ at the ends. You join them end to end, such that their magnetic moments are in same direction. Thus, at the junction the magnetic field ... | https://physics.stackexchange.com |
187,276 | [
"https://dba.stackexchange.com/questions/187276",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/97259/"
] | In a SQL Server database <code>sp_recompile</code> can be run on a stored procedure to update the execution plan. I would like to run this on all stored procedures in a database. Also, I would like to run its equivalent on all table-valued functions but I do not know which sys procedure to run.
Is it possible to do ... | You can run <code>sp_recompile</code> on everything by using a cursor to produce ad-hoc SQL for each and run it, if you think that will help:
<pre><code>DECLARE C CURSOR FOR (SELECT [name] FROM sys.objects WHERE [type] IN ('P', 'FN', 'IF'));
DECLARE @name SYSNAME;
OPEN C;
FETCH NEXT FROM C INTO @name;
WHILE @@FETCH_ST... | If you add memory (even if it's a Hot Added to a VM), and increase Max Server Memory to match, your plan cache will clear out.
That is effectively 'recompiling' all of those things you mentioned, because they won't have a stored plan in cache to re-use. SQL Server will have to build a new one.
You may not have ever ... | https://dba.stackexchange.com |
715,441 | [
"https://physics.stackexchange.com/questions/715441",
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"https://physics.stackexchange.com/users/271469/"
] | The standard textbook approach in Newtonian gravitational dynamics is to derive the particle dynamics using the particle Lagrangian:
<span class="math-container">$$L = T-V = \frac 1 2 m \dot x_u \dot x_u -m\phi(x_u)\tag{1}$$</span>
With the corresponding Euler-Lagrange equation taking the variation w.r.t. <span class="... | <blockquote>
First, is it essential to use two different Lagrangians?
What is the physical basis and meaning of having two Lagrangians?
Is it a rigorous approach?
</blockquote>
No, it is not essential to use two different Lagrangians.
In my opinion it is just a conceptional step before merging
these two partial Lagrang... | The first Lagrangian is the Lagrangian for the motion of a point particle in a Newtonian gravitational potential (or field), whereas the second is the Lagrangian for the gravitational potential (or field), the latter which eventually leads to the Newtonian field equation. So, actually there is no real relationship. Th... | https://physics.stackexchange.com |
45,031 | [
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] | I need to teach my teenage son how to drive. I need the emergency brake in the middle so I can override just in case. I am looking at 4 door sedans from Toyota and Honda between 2007 and 2010. I would like to target my search to only cars that have this feature.
Update: Thank you for your many answers and comment... | If you are concerned that you need it as an over-ride you could consider fitting an extra pedal box and getting brakes that way.
You may find enough room on the bulkhead / firewall to have a simple mechanical linkage that will work. Ask driving schools where they get the work done.
I started both my sons at12 / 13 ju... | As just about everybody else pointed out, the e-brake/hand brake will not stop the car unless the driver is intending to stop the car. 2 things:
<ul>
<li>I once had a leak in the braking system and I did use the hand brake to stop the car at traffic lights just to limp home. I was shifting into neutral and applying th... | https://mechanics.stackexchange.com |
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