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3,293,303 | [
"https://math.stackexchange.com/questions/3293303",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/593426/"
] | I am reading Intro to Math Stats by Hogg, McKean & Craig and I've come across an example that I don't understand, and I am not sure if it's a mistake in the text or not. I disagree with the bold part:
Let <span class="math-container">$X$</span> be a continuous random variable with the pdf <span class="math-contain... | The support of a random variable depends on the context of the problem. For example, you could have a random variable <span class="math-container">$X$</span> with the property that it has support on <span class="math-container">$(0, \infty)$</span>, but it would need to be appropriately normalized in order to be a vali... | Pdfs should satisfy <span class="math-container">$\int f(x)\,dx=1$</span>. You can say that <span class="math-container">$f$</span> has support in <span class="math-container">$(0,\infty)$</span> but in this case, to make sure the above integral valid, we need to determine where <span class="math-container">$f(x)$</spa... | https://math.stackexchange.com |
2,508,120 | [
"https://math.stackexchange.com/questions/2508120",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/500053/"
] | I was wondering how it would be possible to say that there exist 'exactly' $x$ elements within our domain of discourse (without using the uniqueness quantifier?) $x$ can be any positive integer, but it must be a constant.
| Let $T_i=1$ if $Z_i=1$ and $Z_{i+1}=0$ and $0$ otherwise. Note that $ET_i=pq$ and that $T_i T_{i+1} = 0.$ Then $U_n=\sum_{i=1}^{n-1}T_i$ and $$\mathrm{Var}(U_n) = \sum_{i=1}^{n-1}\mathrm{Var}(T_i) + 2 \sum_{i=1}^{n-2}\sum_{j=i+1}^{n-1} \mathrm{Cov}(T_i,T_j)$$
$$ = (n-1)\,\mathrm{Var}(T_1) + 2(n-2)\,\mathrm{Cov}(T_1,T_... | The following is an incorrect treatment (incorrectly assuming independence)... just leaving in place for reference.
Let $J$ be the number of zeros in the sequence, not counting the first element. $J$ is binomial with $n-1$ trials and probability q.
For a sample with $j$ zeros beyond the first element, the number that... | https://math.stackexchange.com |
34,492 | [
"https://softwareengineering.stackexchange.com/questions/34492",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/1338/"
] | Suppose you have an application that reads an input file, on a language that does not support the concept of None. The input is read, parsed, and the contents are stored on a structure for later use.
Now, in general you want to keep into account transformation of the data from the input, such as adding default values ... | This is, of course, a false dichotomy. The real answer is not this simple.
Also the presence or absence of <code>None</code> or <code>Null</code> isn't interesting (or even relevant).
<blockquote>
The first strategy is to perform these transformations at input file reading time.
</blockquote>
In the long run, th... | Proper encapsulation of the problem would suggest that neither solution you presented is correct. An alternative would be to follow choice 2 up to the point that you litter the code with data domain transformations. This should be factored out as a post processing step to be applied after the file is read.
This sepa... | https://softwareengineering.stackexchange.com |
14,598 | [
"https://astronomy.stackexchange.com/questions/14598",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/11589/"
] | So I just learned that CMB redshift is 1100 regardless where we look (up down left right). According to Hubble's Law that makes it around 46 billion light years away, making it the farthest matter away from us. If CMB redshift is the same regardless which direction we look, then how could that be unless we're in the ce... | At the time when the universe was ~380,000 years old it was completely filled with a plasma and light. Light could only travel very short distances (I forget the specifics, but think a couple meters at the most) before being absorbed. So the entire universe was a fog, if you were there and there was an object 10 meters... | We're at the centre of the <strong>observable</strong> universe - but this is because everything (when observed over very long distances) is expanding away from everything else, so we are at the centre of what we observe.
The spherical shape of the observable universe is really an optical illusion, in conjunction with... | https://astronomy.stackexchange.com |
71,534 | [
"https://physics.stackexchange.com/questions/71534",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/25589/"
] | At high-energies when the Higgs field won't affect (interact with) particles, when the symmetry breaking won't occur, what would be $\rm W\pm$ or $\rm Z^{0}$ bosons speed if they would then have a $0$ rest mass? What about Fermions?
| In the unbroken phase of the Standard Model, all particles are massless. Thus, they can only move with the speed of light, in order to fulfill the mass-energy-relation
$$ E^2 = \vec p^2 c^2 + m^2 c^4 = \vec p^2 c^2 \big|_{m = 0} $$
This is true for photons and gluons in our broken world, but would be true for $W^\pm, ... | Originally, you have 3 massless gauge bosons $W_x, W_y, W_z$ for the symmetry $SU(2)_L$ and one massless gauge boson $X$ for the symmetry $U(1)_Y$.
With the higgs mechanism, you have linear combinations of $W_z$ and $X$ which give the massless photon and the massive $Z_0$, while the $W \pm = W_x \pm iW_y$ acquire a ma... | https://physics.stackexchange.com |
51,347 | [
"https://stats.stackexchange.com/questions/51347",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/21559/"
] | I'd like to perform an exponential regression with multiple independent variables (similar to the LOGEST function in Excel)
I'm trying to model the function $Y = b {m_1}^{x_1}{m_2}^{x_2}$ where $b$ is a constant, $x_1$ and $x_2$ are my independent variables, and $m_1$ and $m_2$ are the coefficients of the independent... | As a start:
<pre><code>f <- function(x1,x2,a,b1,b2) {a * (b1^x1) * (b2^x2) }
# generate some data
x1 <- 1:10
x2 <- c(2,3,5,4,6,7,8,10,9,11)
set.seed(44)
y <- 2*exp(x1/4) + rnorm(10)*2
dat <- data.frame(x1,x2, y)
# fit a nonlinear model
fm <- nls(y ~ f(x1,x2,a,b1,b2), data = dat, start = c(a=1, b1=1... | Huub Hoofs' approach above worked! Thank you. Here is the technique I utilized to plot a visualization of the model:
<pre><code># x1 is the variable we want to show on the x-axis
plot(x1, y)
# generate a range of values for x1 in small increments to create a smooth line
xRange <- seq(min(x1), max(x1), length.out ... | https://stats.stackexchange.com |
72,552 | [
"https://dsp.stackexchange.com/questions/72552",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/54413/"
] | Let <span class="math-container">$H(z)$</span> be the rational system function of an LTI system.
How can we show that <span class="math-container">$|H(e^{j\omega})|=|H(e^{-j\omega})|$</span>?
| Your statement only holds true for a real sequence <span class="math-container">$h[n]$</span>.
The frequency response of <span class="math-container">$h[n]$</span> equals to
<span class="math-container">$$H(e^{j\omega}) = \sum_{n=-\infty}^{\infty}h[n] e^{-j\omega n}$$</span>
and if <span class="math-container">$h(n)$</... | A simple counter-example: take a causal two tap FIR filter <span class="math-container">$H(z)=h[0]+h[1]z^{-1}$</span> with <span class="math-container">$h[1]\neq 0$</span>. Now we have <span class="math-container">$H(z^{-1})=h[0]+h[1]z$</span>. Take any <span class="math-container">$z\in\mathbb{C}$</span> satisfying <s... | https://dsp.stackexchange.com |
67,054 | [
"https://softwareengineering.stackexchange.com/questions/67054",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/22695/"
] | In my team, everyone would like to do everything, including backend, frontend, middle layer. I told them that we should divide the work according to roles and area of expertise.
What are the pros and cons of dividing the work vertically (each user story is done by the same person from the back end to the front end) ve... | These here are good advices,I guess the answer depends on your point of view. Here's how I see it...
<ul>
<li>Divide the project vertically so that each iteration when completed yields a usable subset of the whole.</li>
<li>Divide each iteration horizontally as you work together to achieve the goal.</li>
<li>Re-use a... | Break each user story up into tasks, and then see if people want to split them.
The risk is that if one person spends too much time on a certain related set of features then others may not understand that code as well, and that person becomes the expert for problems there.
Since everyone can work on each level, it ma... | https://softwareengineering.stackexchange.com |
713,566 | [
"https://physics.stackexchange.com/questions/713566",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/183646/"
] | What makes us believe that the Cosmological constant was the same in the past?
And if there is no way to prove this then could the age of our Universe be different from the current calculated value since the Universe could be expanded at a different rate in the past?
Even if the Cosmological constant value was differen... | Sinuosoids (and the very closely related exponential function) are eigenfunctions of the derivative operator.
That means if you take the derivative of a sinusoid, the output is another sinusoid of the same frequency.
So if you have an equation that equates sums of derivatives of a function to the function, you are like... | As another answer says, you can use the principles of Fourier decomposition to construct a square wave or any other function you like from a superposition of sinusoids —— or, for that matter, from any other "complete basis" of functions.
However, the physics of the Schrödinger equation is that its eigenvalues... | https://physics.stackexchange.com |
131,223 | [
"https://mathoverflow.net/questions/131223",
"https://mathoverflow.net",
"https://mathoverflow.net/users/34136/"
] | Ground field $\Bbb{C}$. Algebraic category. Elliptic surfaces are those surfaces endowed with a morphism onto some smooth curve, with generic fiber an elliptic curve.
Suppose $E$ is an elliptic curve and consider the ruled surface
$$ S=\frac{E\times\Bbb{P}^1}{G} $$
where $G$ is a group of translations of $E$, acting o... | <strong>EDIT</strong> We show that the answer to the OP's question is <em>yes</em>. Thanks to Will Sawin for his comments.
I use the notation of [Hartshorne, <em>Algebraic Geometry</em>, Chapter V Section 2].
Since $S$ is a ruled surface, there exists a section $C_0$ of minimal self-intersection; set $C_0^2 = -e$. If... | One more attempt.
All the fibers of $p\colon S\to C$ dominate $E$, so they are all isogenous to $E$ and by Kodaira's classification of elliptic fibers they all have smooth support. Hence $p$ is a so-called "quasi-bundle'' and by a result of Serrano [F.Serrano,
Isotrivial fibred surfaces
Ann. Mat. Pura Appl. (4) 1... | https://mathoverflow.net |
149,594 | [
"https://softwareengineering.stackexchange.com/questions/149594",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | In my Programming Language Concepts class it was mentioned in passing that Fortran's original control structures were insufficient. It was alluded that they were too similar to machine instructions for the IBM 704. Was this the case? What exactly made them insufficient?
| Well let's see early versions of Fortran had <code>IF</code> <code>GOTO</code> and <code>DO</code>.
There were several variations on IF and GOTO including ASSIGNED GOTOs and computed GOTO which was sort of like a CASE statement.
So apart from the DO loops all the control statements were variations on IF and GOTO invo... | The bad thing about FORTRAN IV was that all control "structures" (including loops) depended on labels. So they provided unstructured control. They were too powerful. How about, for example branching into a label inside a loop and then, later, branching out again ...
| https://softwareengineering.stackexchange.com |
110,401 | [
"https://physics.stackexchange.com/questions/110401",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/45446/"
] | A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be?
Logically, to me the answer seems to be infinity, as always a fraction of velocity will get reduced. But in my book the answer is n^2/(2n-1) (that comes from energy balance). What i... | <blockquote>
Ayush: Isn't the question telling that the bullet always loses 1/n th of its velocity no matter which plank?
</blockquote>
Based on the answer provided, it seems the writer wanted you to assume that the energy loss per plank is constant. This is not the same as the bullet losing $1/n^\text{th}$ of its... | I think so that the answer is wrong and the answer should be infinite as no plank will take away full velocity of the bullet and it would never stop.Assuming that initial velocity is $u$, velocity after passing through first plank is $(u - u/n)$ ,
then if we assume the length of the plank to be $d$, velocity after pas... | https://physics.stackexchange.com |
277,921 | [
"https://stats.stackexchange.com/questions/277921",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/52874/"
] | We know that sufficient statistic is not necessarily minimal. For example, consider a random sample $X_1,\cdots,X_n \sim \text{Bernoulli}(\theta) $. It can be shown easily that both $T'(X_1,\cdots,X_n) = (X_1,\cdots,X_n)$ and $T(X_1,\cdots,X_n) = \sum_{i=1}^n X_i$ are sufficient statistic. However, $T'$ is not minimal.... | Consider a Normal sample $(x_1,\ldots,x_n)$ from ${\cal N}(0,\sigma^2)$. Then it is a standard result that the statistic$$S(x_1,\ldots,x_n)=\sum_{i=1}^n x_i^2$$is minimal sufficient. If I now define the statistic
$$Z(x_1,\ldots,x_n)=\text{sign}(x_1)\sum_{i=1}^n x_i^2$$where$$\text{sign}(x_1)=\begin{cases} 1&\text{i... | Suppose $T$ and $T'$ are both sufficient statistics of dimension 1 in $\mathbb{R}$, and suppose without loss of generality, that $T$ is minimal sufficient but $T'$ is not.
Then there exists a function $g$ such that $T = g(T')$ but there is no function $f$ such that $T' = f(T)$ (otherwise $T'$ would be minimal suffici... | https://stats.stackexchange.com |
116,730 | [
"https://cs.stackexchange.com/questions/116730",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/-1/"
] | I understand that any assembly programming language has so little abstraction, so that one who programms with it (OS creator, hardware driver creator, "hacker" and so on), would have to know the relevant CPU's architecture pattern very well.
For me, this requirement <em>to know the relevant CPU's architecture pattern ... | The two most obvious characteristics of an assembly language are:
<ol>
<li>It is specific to a particular CPU architecture.</li>
<li>There is a one-to-one correspondence between assembly language commands and machine code instructions (once you strip out labels, assembler directives and code comments).</li>
</ol>
By ... | The essential difference between assembly language and every other programming language is that assembly language specifies the sequence of instructions directly, whereas in any other language, the code has to be converted into a sequence of instructions, a process known as <em>compilation</em> or <em>code generation</... | https://cs.stackexchange.com |
47,593 | [
"https://dsp.stackexchange.com/questions/47593",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/33902/"
] | In image processing we may use derivatives to help us detect the edges. While at mean time, this operation would also make the data noisier. But why do we have this effect?
My intuition is that if we denote the image data as
$I_{actual}(x, y) = I_{ideal}(x, y) + I_{noise}(x, y)$.
Then apparently when we do $I_{actua... | Differentiation in one axis will amplify high-frequency components. Assuming noise at Fs/2 (i.e maximum frequency), the gain at this frequency will be 6 dB. Intuitively, if you have a sequence alternating between +1 and -1 i.e (1, -1, 1, - 1), Then the difference will be +2, - 2, +2, -2, a gain of 6 dB
Another reason ... | Let's have a look at:
$$\Delta I (x_1,x_2) = I_{actual}(x_2, y) - I_{actual}(x_1, y) = I_{ideal}(x_1, y) + I_{noise}(x_1, y)
- I_{ideal}(x_2, y) - I_{noise}(x_2, y)$$
If you assume that for close $x_1$ and $x_2$ the $I_{ideal}$ doesn't change much so that
$$ I_{actual}(x_2, y) \approx I_{ideal}(x_2, y)$$
then
$$\De... | https://dsp.stackexchange.com |
13,656 | [
"https://stats.stackexchange.com/questions/13656",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/5582/"
] | I have a line and I have detrended it but it seems to still have a trend. Visually it has one (see jpg) and it has a unit root (Dickey-Fuller) and fails the Durbin-Watson test, so it is not stationary.
The line that I am calling 'detrended' is a plot of the residuals (errors) of a regression of the data on time.
My que... | It would still have a trend if you have not properly detrended it. Trends are a complicated thing, and you may want to re-visit the model you are using to describe the trend.
First of all, if you're using a linear model, it is almost certainly wrong. You can clearly see a unit root, where the shock in September '06 ... | At a more basic level aren't you assuming that the original graph has two parts that have the same slope but different intercepts, so if you throw a linear regression through it, the regression line should share that slope and split the difference in intercepts?
This isn't true. Try using the points
<pre><code>x=(1, ... | https://stats.stackexchange.com |
291,112 | [
"https://physics.stackexchange.com/questions/291112",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/135336/"
] | I could get the dispersion relation for a wave traveling in a rectangular waveguide of width $a$
$$\omega=c\sqrt{ \left( \frac{\pi}{a}\right)^2 + k_{z}^2 }$$
with $k_z = \dfrac{2\pi}{\lambda_g}\,.$
where z is the direction along the guide. From here I got the group velocity
$$ \dfrac{\partial\omega}{\partial k_z} ... | The expression of the group velocity $$v_g=\frac {\partial \omega}{\partial k_z}$$ for the waveguide with wave vector $k_z$ in propagation direction is correct. And the phase velocity is $$v_{ph}=\frac{\omega}{k_z}$$ According to the dispersion relation of the wave guide, when $\omega$ approaches the cut-off frequency ... | Good question. Guided wavelenght is a somewhat tricky concept. Let's see if we can get some intuition for it.
The group velocity is the straight line velocity of propagation of the wave down the center-line of the waveguide. Its value is always less than the propagation velocity of the wave in free space ($c$), becau... | https://physics.stackexchange.com |
3,251,164 | [
"https://math.stackexchange.com/questions/3251164",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/109263/"
] | Consider <span class="math-container">$H$</span> be a separable Hilbertian space with real inner product <span class="math-container">$\langle , \rangle $</span>. Let <span class="math-container">$\Gamma: H \to H$</span> be a Nuclear operator
<span class="math-container">$$\Gamma(u) = \sum_{n=1}^\infty \lambda_n \lang... | Let <span class="math-container">$u_n\rightharpoonup u$</span>. Fix some index <span class="math-container">$N$</span>. Then
<span class="math-container">$$
\|u_n-u\|_*^2 = \sum_{i=1}^\infty \lambda_i\langle u-u_n,\phi_i\rangle^2
= \sum_{i=1}^N \lambda_i\langle u-u_n,\phi_i\rangle^2 + \sum_{i=N+1}^\infty \lambda_i\lan... | From the compactness of <span class="math-container">$\Gamma^{1/2}$</span>,
the weak convergence <span class="math-container">$u_n \rightharpoonup u$</span>
implies <span class="math-container">$\Gamma^{1/2} (u_n - u) \to 0$</span>,
hence <span class="math-container">$\|u_n - u\|_\star \to 0$</span>.
| https://math.stackexchange.com |
100,601 | [
"https://softwareengineering.stackexchange.com/questions/100601",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/32827/"
] | I have to create an Adapter between two software (mech. simulation, non-cs). Assuming we have a class named <code>ThatThing</code>. I have to handle various vendor specific implementations. These versions don't have meaningful names (unlike eclipse helios, indigo etc.).
<strong>1. How should I name a class that should... | Use a different package name.
<pre><code>com.example.version36.ThatThing
com.example.version37.ThatThing
</code></pre>
This allows you to keep all the "things" for specific versions together.
Apache Commons Lang used this format when releasing their "version 3" rewrites.
<hr>
Since you need to be able to reference... | It doesn't matter a lot. Pick a convention that expresses everything you need it to express and stick with it.
You could use <code>ThatThing3_6</code> for "That Thing 3.6".
| https://softwareengineering.stackexchange.com |
30,797 | [
"https://biology.stackexchange.com/questions/30797",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/4717/"
] | I have to perform an RNA extraction that should start with 900 uL of 2%SDS bacterial solution. The problem is that the sample is in 900 uL of PBS.
I thought about centrifugation of the sample at 5ºC, remove PBS and then add the 2%SDS.
DO you think bacterial RNA quantities will vary?
Thanks!
| PBS is isotonic to most cells, so in this buffer your bacterial cells are intact. Centrifuging them to remove PBS won't harm them it is quite standard procedure. You have to be careful after adding 2% SDS because it will lyse your cells and then the RNA contained within them will become "free" and RNAs are fragile mole... | I'm assuming that you have a solution of bacteria in your buffer directly after growing them for some time, and without performing a lysis step yet. The 2% SDS step looks like it is for lysis of your cells.
In that case, centrifuging the bacteria and resuspending them in lysis buffer is a very common step in many prot... | https://biology.stackexchange.com |
18,031 | [
"https://mathoverflow.net/questions/18031",
"https://mathoverflow.net",
"https://mathoverflow.net/users/83/"
] | A couple weeks ago I attended a talk about the Keel-Mori theorem regarding existence of coarse moduli spaces for Deligne-Mumford stacks with finite inertia. Here are some questions that I have been wondering about since then: What are some applications of this theorem? What does it matter if a DM stack has a coarse spa... | An example is Deligne's theorem on the existence of good notion of quotient $X/G$ of a separated algebraic space $X$ under the action of a finite group $G$, or relativizations or generalizations (with non-constant $G$) due to D. Rydh. See Theorem 3.1.13 of my paper with Lieblich and Olsson on Nagata compactification f... | May I suggest rephrasing the question to something like: Are there any results in the theory of stacks that rely on the existence of an underlying coarse moduli space?
| https://mathoverflow.net |
131,385 | [
"https://physics.stackexchange.com/questions/131385",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/57317/"
] | In Ampere's law, the current outside the curve taken is not included in the expression. Does it mean that the magnetic field calculated by using the law gives the contribution of only the currents crossing the area bounded by the curve?
| The value of the line integral $\oint_C \vec B \cdot d\vec l$ really does only depend upon the current bounded by the closed path $C$. That's a consequence of Ampere's law. <strong>However,</strong> the value of the magnetic field $\vec B$ at any point along the path $C$ depends on every current, even those outside.
Kn... | It would be nice to provide a picture or diagram to make the question a little more clear.
The answer is that the curve of integration (to find the associated magnetic field) <strong>should cover</strong> the area or loop into which the current flows, as such there is <strong>no current outside</strong> which is not t... | https://physics.stackexchange.com |
938,400 | [
"https://math.stackexchange.com/questions/938400",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/102617/"
] | 1) Is it possible to weight two coins in such a way that if the two coins are tossed, the three possible outcomes (both heads, both tails, or one head and one tail) all have probability $\frac{1}{3}$? The two coins do not have to be weighted the same as each other.
2) What about three coins? Can you weight them so tha... | We deal with the general case of $n\ge 2$ coins.
Let the $i$-th coin have probability $p_i$ of landing heads, and $q_i$ of landing tails. (Of course $p_i+q_i=1$, but that will turn out to be of no importance!)
Then the probability of $k$ heads and $n-k$ tails is the coefficient of $x^k$ in the product
$$(p_1x+q_1)(... | Let $p,q$ denote the respective bias of the first and second coin:
$$
\mathbb{P}\{C_1=\mathsf{Heads}\} = p,\qquad \mathbb{P}\{C_2=\mathsf{Heads}\} = q
$$
Then, as long as $p,q\in[0,1]$ satisfy $p+q=1$ and $pq=1/3$, one can easily show the three conditions are satisfied (this is necessary):
\begin{align}
\mathbb{P}\{C_1... | https://math.stackexchange.com |
262,855 | [
"https://softwareengineering.stackexchange.com/questions/262855",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/156226/"
] | I've been doing web programming for a long time now, and somewhere, I lost track of why we are doing what we are doing today (or how did we come to do things this way)?
I started out with basic ASP web development, and very early on, display and business logic were mixed on the page. Client-side development varied wi... | Shifting the computing load between the server and the client is a cyclical phenomenon, and has been so for quite some time.
When I was in community college the Personal Computer was just getting a head of steam. But Ethernet was not in widespread use yet, and nobody had a local area network. Back then, the college ... | You seem to be mixing two very different concepts:
<ol>
<li>Separating presentation and business logic (MVC) => increase maintainability</li>
<li>Assigning execution to a node => increase efficiency</li>
</ol>
Back in the days Client/Server computing was often confused to imply the first because clients generally did... | https://softwareengineering.stackexchange.com |
668,117 | [
"https://physics.stackexchange.com/questions/668117",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/245410/"
] | This is a homework question, I will make it as concise as possible:
<blockquote>
A 1-way plane trip is 2800km and the plane's airspeed is 790km/h. The plane flies with the wind on the way there, and against it on the way back. It took 1 hour longer going from point B to A (returning flight) than to go from A to B (to t... | <span class="math-container">$\require{cancel}$</span>
<span class="math-container">$$\frac{2800}{t_1}-r_a=\frac{-2800}{t_1+1}+r_a$$</span>
<span class="math-container">$$\xcancel{\frac{2800}{t_1}=\frac{-2800}{t_1+1}}$$</span>
Did you add <span class="math-container">$r_a$</span> to both sides or subtract <span class="... | Given that <span class="math-container">$v$</span> equals the speed of the wind, an equation that represents the time of travel of the airplane for the forward and return trips, in terms of velocities and distances, is:
<span class="math-container">$$\frac{2800}{790-v}=\frac{2800}{790+v}+1$$</span> <span class="math-co... | https://physics.stackexchange.com |
23,940 | [
"https://mathoverflow.net/questions/23940",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5801/"
] | This is a question of the motivation for a common assumption found in the literature.
The free topological group $F(X)$ on a space $X$ exists for all spaces $X$ (It seems this was first shown by Katutani and Samuel). I mean "free topological group" in the sense that $F:Top\rightarrow TG$ is left adjoint to the forgetf... | Let <span class="math-container">$X$</span> be a topological space. If <span class="math-container">$F(X)$</span> is <span class="math-container">$T_0$</span> then I think <span class="math-container">$F(X)$</span> is isomorphic (as topological groups) to <span class="math-container">$F(Y)$</span>, where <span class="m... | Hi.
This is mainly because one wants to have $X$ as a subspace of $F(X)$. Since every topological group is tychonoff (:=closed sets can be seperated from points outside by continouos functions) and so is every subspace. So being Tychonoff is necessary (and sufficient) for $X$ being a subspace of $F(X)$.
| https://mathoverflow.net |
311,492 | [
"https://stats.stackexchange.com/questions/311492",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/183315/"
] | I'm having trouble doing a forecast based on previous data. I have data that represents eight years worth of monthly data $(n=96)$, for number of sales. I want to forecast the next 12 months based on this data using an optimal linear forecast, and I want to provide the variance of this forecast.
Here is the data
<pre... | The first equation of the question as the M step is incorrect (and Andrew Ng does not use this equation as the M step but as an argument to show EM increases the observed likelihood at each step of the algorithm).
The correct M step is the derivation of
$$\arg\max_\theta\mathbb{E}[\log p(x,Z|x,\theta) | \theta^{(t)}]$... | In the very last equation: What you get is indeed the same as above:
$$\sum_z p(z|x)p(x) = \sum_z \frac{p(z,x)}{p(x)}p(x) = \sum_z p(z,x) = p(x)$$
| https://stats.stackexchange.com |
1,577,176 | [
"https://math.stackexchange.com/questions/1577176",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/232077/"
] | I see this pretty much everywhere, but I'm still not really sure what it means. I've heard the explanation that it "maps the third dimension onto the second dimension," but even that doesn't make sense to me. Could someone elaborate?<br/> An example: Suppose that $F : \mathbb{R}^2\rightarrow\mathbb{R}$ and $f : \mathbb... | When someone writes
$$f : X \rightarrow Y $$
They are using notation to explain something about the function $f$. In particular this spells out what the <em>domain</em> and <em>codomain</em> spaces are. For
$$f : \Bbb{R}^3 \rightarrow \Bbb{R}^2$$ it means that the function takes input from $\Bbb{R}^3$ and has output va... | An application $f$ from $\mathbb{R}^3$ to $\mathbb{R}^2$ is a function that for all vectors of $\mathbb{R}^3$ gives one (and only one) vector of $\mathbb{R}^2$.
There are <strong>a lot</strong> of examples:<br>
$f=0$. This map sends every $(x,y,z)$ to $(0,0)$<br>
$f(x,y,z) = (x,y)$. This map ignores the third coordina... | https://math.stackexchange.com |
104,548 | [
"https://chemistry.stackexchange.com/questions/104548",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/40365/"
] | For my science classes, I have built multiple types of electrochemical batteries utilizing oxidation-reduction reactions, and I have demonstrated that they each produce potential difference across the different solid metals used using a voltmeter. Unfortunately, I have been unable to harness any of this to light up a ... | Your experimental procedures seem to be perfect. There is just one minor error in your conclusion: you said that no current flowed. I disagree - current flowed, just not as much as you hoped. Harnessing one of these reactions to light up even the teeniest lightbulb would be similar to harnessing a bumblebee to a model ... | You could try considering the Cottrell equation, Randles–Sevcik equation or the mass transfer limiting case of the butler-volmer equation
<span class="math-container">$$
i = \frac {nFAc_{j}^{0}\sqrt{D_{j}}}{\sqrt{\pi t}}
$$</span>
i = current, in unit A
n = number of electrons (to reduce/oxidize one molecule of ana... | https://chemistry.stackexchange.com |
10,994 | [
"https://computergraphics.stackexchange.com/questions/10994",
"https://computergraphics.stackexchange.com",
"https://computergraphics.stackexchange.com/users/6165/"
] | I'm just trying to figure out, how rounded corners are usual drawn for user interfaces in a performant way & as insight also try to figure out how it's done in Browser, as they allow for variable round corners (without being blurry) :)
In the end I try to use some of this information for the implementation of the u... | The choice of various tristimulus color spaces or spectral rendering matters when you're doing <em>multiplicative</em> color operations, like multiplying a light source color by a material reflectance. For these operations, the spectral approach is most accurate, and multiplying tristimulus color values is a pretty coa... | <blockquote>
How accurate it is to estimate rendering equation using wavelengths
</blockquote>
This is probably as accurate as it gets if you are using with the full form of Fresnel equation.
<blockquote>
then convert result to CIE XYZ
</blockquote>
This brings in two problems with respect to accuracy.
If the spectral ... | https://computergraphics.stackexchange.com |
602,724 | [
"https://physics.stackexchange.com/questions/602724",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/259747/"
] | The problem says:
<blockquote>
A bullet hits a block kept at rest on a smooth horizontal surface and gets embedded into it. Which of the following does not change?
A. Linear momentum of the block
B. Kinetic energy of the block
C. Gravitational potential energy of the block
D. Temperature of the block.
</blockquote>
My ... | In the usual situation, where the quantum state is on the right (a ket), like <span class="math-container">$A^{\dagger}A^{\dagger}A^{\dagger}A|\psi\rangle$</span>, you do indeed apply the (annihilation) operator on the far right first, and then successively to the left. If you have trouble remembering this, think of i... | With any operators acting on a ket <span class="math-container">$| \psi \rangle$</span>, you apply the one farthest to the right first. So in your case <span class="math-container">$A$</span>.
| https://physics.stackexchange.com |
103,222 | [
"https://electronics.stackexchange.com/questions/103222",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/38823/"
] | I just started studying Arduino and I'm watching a online course. I got into the stage where we're suppose to build some sort of protection system so we can plug-in outsourced power supply and prevent the arduino uno from frying.
My problem is that the class course uses a 2N222 Transistor and he talks about \$V_{ce}\$... | Your understanding is correct, in that you have to careful about subjecting your I/O pins directly to external devices. Sometimes, that is because the external device requires a different (usually, when it is a concern, this means higher) voltage than your I/O pin can provide or tolerate. Sometimes, that is because the... | The 2N2222 (note the four 2s, not 3) or 2N2222A are common jellybean NPN small signal transistors. Just about any small signal NPN transistor that can handle a few 100 mA collector current will probably work. I prefer the somwhat more robust 2N4401 for my small signal NPN jellybean applications, but there are many tr... | https://electronics.stackexchange.com |
14,979 | [
"https://biology.stackexchange.com/questions/14979",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/86/"
] | Assume you have an exam which has 5 extensive questions and 60 minutes.
You do not have time to cover most if you write everything in essay format.
If you start to write essays, you do not really have time to cover all mechanisms and so on.
I just heard that one student did the exam with by list format, for instance
... | Given the highly variable nature of such processes and systems, it's unlikely that a common standard is feasible or sensible. In medical questions, a bottom-up order like in your example usually makes sense, starting with the most specific known cause and deriving from there until you arrive at the symptoms. Treatments... | I usually answer in a extensive and descriptive way, and I try to put as much information as possible. If it's a process I usually add a little diagram. If there are lot of attributes to add sometimes I do lists, but usually teachers don't like them an it's easier to find errors or lacks in lists.
There is no standard... | https://biology.stackexchange.com |
207,291 | [
"https://dba.stackexchange.com/questions/207291",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/133835/"
] | I'm using PostgreSQL 9.6 and have the following table:
<pre><code>CREATE TABLE eco.tracks (
id bigserial NOT NULL,
time_track timestamp NOT NULL,
track bigint ,
distance_1 int ,
CONSTRAINT pk_tracks PRIMARY KEY ( id )
);
</code></pre>
A... | assuming you have an index on time_track
move the offsets to the other side of the inequality so that the arithmetic is only done once and so that an index on time_track can be used.
<pre><code>SELECT (track, distance_1, aircraft_time)
FROM eco.tracks
WHERE time_track >= (%s) + INTERVAL '10 seconds'
and t... | You can determine the time interval in the application and use a query like:
<pre><code>SELECT (track, distance_1, time_track)
FROM tracks
WHERE time_track BETWEEN (%s) AND (%s)
AND distance_1 IS NOT NULL
ORDER BY distance_1 asc
LIMIT 1;
</code></pre>
An index like:
<pre><code>CREATE INDEX ... (time_track, dist... | https://dba.stackexchange.com |
123,282 | [
"https://electronics.stackexchange.com/questions/123282",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/16307/"
] | I apply a constant 4ma current I to a resistor R and I measure a voltage V across.<br>
so the resistor \$ R = \dfrac{V}{I}\$.
But when I apply \$ I_2=20ma\$ to the same resistor R and I obtain the voltage \$V_2\$ then the resistor \$R= \dfrac{V_2}{I_2}\$ I expect the same.
but in first case for 4ma, I obtain 248.2 ... | Perhaps check the temperature coefficient of the resistor. With 20mA, the power dissipation in the resistor is 25x larger than with 4mA (power dissipation is proportional to I<sup>2</sup>). The resistor heats up as you increase your current. As it heats up, its resistance changes. Incorporating the temperature coeffici... | <ol>
<li>Use a lower resistance value. A smaller resistor will heat itself less for the same current. Values below 1 ohm are often used for current measurement applications.</li>
<li>Use a resistor with a lower TCR. Certain types of resistors (for example, wirewound types) have much lower TCR than others. </li>
</ol>
... | https://electronics.stackexchange.com |
31,523 | [
"https://stats.stackexchange.com/questions/31523",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/4048/"
] | I have data from an experiment where I measured the $CO_2$ from:
<ul>
<li>4 different dissolved organic carbon (DOC) solutions </li>
<li>each at 4 different concentrations </li>
<li>each in light and in dark. </li>
</ul>
Each combination of DOC source, concentration, and light occurred only once (e.g., only one jar ... | I agree with your assessment that the 4 measurements of a jar are pseudo-replicates, and the easiest way of dealing with it is to combine them into one value (I think you are creating a rate, but any meaningful combination could be used). Let's concentrate on modeling one $Y$ value per jar. Consider the ANOVA table for... | I think you're believing "replication" in this instance to mean sampling a unit with the exact same concentration and light which is inherently continuously valued. Obviously, this is impossible to do with any moderately sensitive equipment. It's also something that arises in real life, no two units are the same, but i... | https://stats.stackexchange.com |
141,795 | [
"https://softwareengineering.stackexchange.com/questions/141795",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27367/"
] | I understand the role of the model and view in the Model-View-Controller pattern, but I have a hard time understanding why a controller is necessary.
Let's assume we're creating a chess program using an MVC approach; the game state should be the model, and the GUI should be the view. What exactly is the controller in ... | Using your example the Controller would be what decided what was a legal move or not. The Controller would let the view know how to arrange the pieces on the board at start up using the information it received from the Model. There are more things that can be handled by the Controller but the key is to think about Busi... | <blockquote>
Why not just perform all the logic on the model in the view itself?
</blockquote>
The controller is the glue that binds the model and view together, and it's also the insulation that keeps them apart. The model shouldn't know anything about the view and vice versa (at least in Apple's version of MVC). T... | https://softwareengineering.stackexchange.com |
703,737 | [
"https://physics.stackexchange.com/questions/703737",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/82364/"
] | It is very difficult to hear underwater sounds from above the surface of a body of water. This is suggested to be due to the speed of sound being very different in air versus water, leading to most underwater sound being reflected back into the water, and not passing into the air.
Am I supposed to think of the air-wate... | Within reason, a thick sheet of water and a thin one will affect sound mostly the same.
With extremely large thicknesses, sound actually transmits better.
When the thickness approaches a wavelength of the sound in question, the equations get a bit more complicated. I'd be wary of venturing a guess in this regime.
| Yes but not directly because of the speed of sound. It's analogous to Snell's Law in optical reflectivity, or to VSWR in microwave components. The effective "index of refraction" for sound changes drastically at a water-air interface, thus leading to a lot of reflection and not much transmission.
This holds... | https://physics.stackexchange.com |
39,862 | [
"https://quant.stackexchange.com/questions/39862",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/34296/"
] | For an option expiring at a particular date I have
<pre><code>Moneyness 0.4,0.7,0.85,0.95,1,1.05,1.15,1.3,2.5
Vol 0.105,0.075,0.045,0.045,0.202,0.045,0.045,0.075,0.085
</code></pre>
How do I get the volatility for an option with a particular moneyness? Do I interpolate with an 8th degree polynomial? How would ... | The interpolation of the implied vol surface is no easy task unfortunately and it is subject of extensive research.
This is because you want the vol surface to have some nice characteristics, e.g.: be smooth, non arbitrable, etc.
Two approaches exist:
<ul>
<li>Assuming a parametric form for the volatility surface an... | I would say the best solution will be curve fitting, which is definitely not an easy solution.
Depends on whether you are fitting interest rates or stocks/commodities. You might try <strong>SABR</strong> for the former and <strong>SVI</strong> for the letter. There are lots of papers about them that you should easily ... | https://quant.stackexchange.com |
15,175 | [
"https://security.stackexchange.com/questions/15175",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/9378/"
] | As we all know, routers that you buy from the store come preset to hand out IP addresses using DHCP, generally on one of three networks: 10.0.1.1/24, 172.16.0.1/24, and 192.168.1.1/24. I personally restrict DHCP to a smaller range and use DHCP reservations based on MAC address to make touching network devices through S... | The security measures which are the primary subject of your question here (MAC filtering, non-standard IP addressing) basically equate to "security through obscurity". They are <em>very</em> weak against a dedicated attacker, and so should not be relied upon as the only security functions in your system.
That said, e... | While having a "random" local network subnet will not normally help you against an attack, there have been both CSRF attacks and trojan or virus-driven attacks that expect a certain local network configuration. The expected configuration is, in almost all of these cases, is to have the gateway at either 192.168.0.1 or ... | https://security.stackexchange.com |
17,177 | [
"https://softwareengineering.stackexchange.com/questions/17177",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/6208/"
] | Just out of curiosity what's the difference between a small, medium and large size project? Is it measured by lines of code or complexity or what?
Im building a bartering system and so far have about 1000 lines of code for login/registration. Even though there's lots of LOC i wouldnt consider it a big project because ... | Complexity.
The more complexity, the harder it is to learn everything in the project.
| Roughly how I'd accord things -- keep in mind this is more or less arbitrary. The "size" of the project in a composite of other factors like complexity, source lines of code, number of features/business value, etc. A very small product can deliver a large amount of value, etc. That being said:
<ul>
<li><strong>2m+ slo... | https://softwareengineering.stackexchange.com |
53,154 | [
"https://cs.stackexchange.com/questions/53154",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/45910/"
] | I am almost totally uneducated in programming and computer science in general, though I am really fascinated by these topics. I read that mathematics is important in programming and that nowadays many mathematicians specialise in applied mathematics in this field. So, I wonder how these two branches are linked with eac... | You don't need any math to write a Hello World or a very simple website.
You will need to know some discrete mathematics and algorithm analysis to write a program that finds a route between two cities.
You will need to know matrix transformations and quaternions to write a game engine.
You will need to know a lot ab... | You pose two questions.
<ol>
<li>Which is the role of mathematics in programming?</li>
</ol>
Quite fundamental. It is the universe of computers and programs. I mean no exaggeration. It describes the framework in which they exists. It provides the tools to analyze computer programs, e.g. it is used to prove the correc... | https://cs.stackexchange.com |
134,109 | [
"https://cs.stackexchange.com/questions/134109",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/128255/"
] | Let <span class="math-container">$\ f_1, f_2, ... f_m : \{0, ..., m \} \rightarrow \mathbb Z $</span>
my task is to find an algorithm that find a series of numbers <span class="math-container">$\ x_1, x_2, ..., x_m \in \{ 0, ..., m \} $</span> that maximise <span class="math-container">$\ \sum_{i=1}^m f_i(x_i) $</span>... | Following is a trivial Dynamic Programming algorithm for your problem:
Let <span class="math-container">$T$</span> denote a table of size <span class="math-container">$(m+1)$</span> x <span class="math-container">$(m+1)$</span>.
Here, <span class="math-container">$T[i][j]$</span> stores the maximum value of <span class... | This problem can be solved using dynamic programming.
For <span class="math-container">$i \in \{1, \dots, m\}$</span> define <span class="math-container">$F_i(x)$</span> as the maximum value <span class="math-container">$\sum_{j=1}^i f_j(x_j)$</span> attainable for a suitable choice of <span class="math-container">$x_1... | https://cs.stackexchange.com |
17,725 | [
"https://dba.stackexchange.com/questions/17725",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/2502/"
] | I found that my database, specifically the <code>USERS</code> tablespace, dramatically increased in size.
How can I find what DML operations are performing on the objects located in this tablespace?
| The query below will show you an overview of the schemas, tablespaces and objects in your database and their respective sizes.
<br/>
<br/>- Change the group by to decrease the level of detail (you might want to see if the size is being caused by tables, indexes or other objects first)
<br/>- Add a where clause to only... | Another check I would recommend is find out which users have a quota for the USERS tablespace. Also check who has UNLIMITED TABLESPACE system privilege. If you find any account with the UNLIMITED TABLESPACE privilege, unless it is the DBA's account, remove it and provide specific quotas to tablespaces based on need (... | https://dba.stackexchange.com |
37,637 | [
"https://cs.stackexchange.com/questions/37637",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/20154/"
] | I know from Schaefer's Dichotomy Theorem that only a few types of satisfiability problems are in P and any other problem is NP-complete. However, all of the algorithms I know for them use specific techniques unique to that type of problem- e.g. unit propagation for Hornsat, linear algebraic techniques mod 2 for XORSA... | Schaefer's dichotomy theorem is proved by dividing CSPs into two types: those that can be reduced to one of a few specific problems in P, and the other to which SAT can be reduced (and so are NP-complete). Specifically, every CSP of the former type is either trivial (always satisfied by the constant 0 or the constant 1... | Look for papers/books written by Vijay Chandru, John Hooker and John Franco. Some of their techniques use Integer Programming (looking at special structures in the matrix generated by the CNF clauses of the SAT instance). The "extended Horn" formulas have a special structure when represented as graphs which make them... | https://cs.stackexchange.com |
542,537 | [
"https://physics.stackexchange.com/questions/542537",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/158819/"
] | I am writing a simplified simulation of how a drone will move to a target destination. The drone adjusts the acceleration based on the distance from the target location.
I want to use the equation for acceleration where c is the target location:
<span class="math-container">$$a(t) = c - x(t)$$</span>
That makes the v... | <ol>
<li>The statement is true for pure states: For <span class="math-container">$\rho_{AB}=|\psi\rangle\langle\psi|$</span>, write <span class="math-container">$|\psi\rangle=\sum\lambda_i|i\rangle_A|i\rangle_B$</span> in the Schmidt basis. Then the claim is immediate, since the support of <span class="math-container"... | Assume <span class="math-container">$\rho\equiv\rho_{AB}$</span> is pure, <span class="math-container">$\rho=|\Phi\rangle\!\langle\Phi|$</span>,
and write its Schmidt decomposition as <span class="math-container">$|\Phi\rangle=\sum_k \sqrt{p_k} |u_k\rangle|v_k\rangle$</span>. Notice that the reduced states then have th... | https://physics.stackexchange.com |
269,232 | [
"https://stats.stackexchange.com/questions/269232",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/154208/"
] | I'm still trying to understand dropout completely, but this is what think is happening so far:
<ol>
<li>At each step there is a chance <em>p</em> of a unit being set to zero.</li>
<li>If a rectified linear unit (ReLU) is used for activation, then a weight of zero can often result in 'dead' units.</li>
<li>If I run a n... | I think you're conflating the dead ReLU problem and dropout. ReLU nets often use dropout, but they are not the same.
<strong>Dropout</strong>
Using dropout "freezes" some units (at random and usually but not always independently) by ignoring their weights at each iteration. The frozen units are not <em>set</em> to z... | generally speaking, if one keeps the learning rate not too high, empirically units tend not to be hard-dead: there will still be at least a few data points with a gradient that 'saves' them. Whether that means if you trained to infinity, on a small enough learning rate, are you guaranteed they would / wouldnt all die, ... | https://stats.stackexchange.com |
90,050 | [
"https://softwareengineering.stackexchange.com/questions/90050",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27844/"
] | Would you include an XML schema for a new file format in a software specification document or would you consider this too specific? Or would it be already too specific to require XML at this point?
| If the schema already exists, then I don't see why you wouldn't want to specify that your system must use a particular schema (and version of that schema) for data storage or transfer. This sounds like a non-functional requirement to me, specifically what Karl Wiegers refers to as either a Software Interface Requiremen... | If it's a high-level specification which just says "System X will do task Y with file Z", then yes, it's too specific. If it's a detailed spec that says "System X will implement a web service to perform task Y using XML file Z that is sent from client system A", then yes, you should include the schema. It does not have... | https://softwareengineering.stackexchange.com |
4,476,377 | [
"https://math.stackexchange.com/questions/4476377",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1060744/"
] | <strong>Problem (skip to part d):</strong> Ignoring leap days, the days of the year can be numbered <span class="math-container">$1$</span> to <span class="math-container">$365$</span>. Assume that birthdays
are equally likely to fall on any day of the year. Consider a group of <span class="math-container">$n$</span> p... | <blockquote>
While <span class="math-container">$\frac{365}{2}$</span> different birthdays would have a <span class="math-container">$50$</span> percent chance of matching your birthday
</blockquote>
You said that you get how a person's birthday has a <span class="math-container">$50\%$</span> chance of landing in one ... | Given <span class="math-container">$n$</span> people, for <span class="math-container">$k \in \{1,2,\cdots,n\},$</span> let <span class="math-container">$E_k$</span> denote the event that person-<span class="math-container">$k$</span> shares your birthday. Suppose that you assume <span class="math-container">$\color{r... | https://math.stackexchange.com |
114,902 | [
"https://electronics.stackexchange.com/questions/114902",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/35745/"
] | How accurate is the proximity feature in BLE, can I detect if two BLE are touched tougether?
| The "proximity" feature in BLE is actually based on signal strength of the packets it receives (RSSI).
The RSSI changes very little with distance when the devices are far away, and disturbances play a large role in the RSSI value making it a very unreliable as a direct distance measure in the far field.
However wh... | I did some work on proximity with iPhones talking to CSR1001/1001 devices and found the RSSI to be highly variable depending on a number of factors. My experience was it was difficult to detect distance any kind of accuracy. E.g. moving 15 metres away (line of sight) has the same effect as putting the item in your po... | https://electronics.stackexchange.com |
294,665 | [
"https://dba.stackexchange.com/questions/294665",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/55628/"
] | Now I am install PostgreSQL 13 in remote cloud server and expose the 5432 port to public network. I add a whitle list in PostgreSQL config file <code>pg_hba.conf</code> like this:
<pre><code>host all all 127.113.122.1/24 scram-sha-256
</code></pre>
which <code>127.113.122.x</code> i... | Pick a very good password and then don't share it with any other accts and don't leak it. Hackers generally break into cloud postgresql servers by guessing crappy passwords, not by guessing good ones. Then open up pg_hba to everyone, or at least the entire range of your isp.
Better yet, do this only for your nonsupe... | This will let all ip adresses starting with 127.113.122
<pre><code>host all all 127.113.122.0/24 scram-sha-256
</code></pre>
This will let all ip addresses starting with 127.113
<pre><code>host all all 127.113.0.0/24 scram-sha-256
</code></pre>... | https://dba.stackexchange.com |
466,033 | [
"https://electronics.stackexchange.com/questions/466033",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/235602/"
] | I would like to know if charging 7 lithium-ion batteries in series with BMS 7S are faster than simply charge them in parallel. Please for your advice, thank you!
| Be very careful with powerful chargers to charge your li ion.
One cell can handle 1A load current the other 20A
Don't mix load current with the famous C, if a cell is 3000mah @ 1C your max charge is 3A.
If it is 0.5C it would be max 1.5A charge
Look up the cell specs and adjust your charger to there max.
If a cell is ... | If you have a 10 watt charger, and batteries with 10Wh capacity, they will take an hour to charge, whatever the configuration.
Now if you have a 7S battery, you'd better be using a 7S charger. If a 7P battery, then a charger that can handle 1S will be required.
It may be easier/cheaper to find a high powered charger ... | https://electronics.stackexchange.com |
419,088 | [
"https://mathoverflow.net/questions/419088",
"https://mathoverflow.net",
"https://mathoverflow.net/users/342793/"
] | Can such a set <span class="math-container">$A=$</span> {<span class="math-container">$a_1,.. a_k$</span>} exist, such that:
<ol>
<li><span class="math-container">$\sum_i a_i = 1$</span> and <span class="math-container">$a_i $</span> are rational positive numbers</li>
<li><span class="math-container">$k$</span> is and... | Multiply by the least common multiple <span class="math-container">$M$</span> of the denominators to get the equivalent problem:
<ol>
<li>The <span class="math-container">$a_i$</span> are positive integers.</li>
<li><span class="math-container">$k$</span> is an odd number.</li>
<li>We can partition <span class="math-co... | In fact it follows from the proof by @PeterTaylor that there are no solutions over the reals. Indeed, if we drop condition 3 then we can have solutions, <span class="math-container">$k$</span> is odd and all the <span class="math-container">$a_i$</span> are equal. But that is all.
I suspected that the following was tru... | https://mathoverflow.net |
106,597 | [
"https://softwareengineering.stackexchange.com/questions/106597",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/31418/"
] | There are advantages in holding daily scrum, like:
<ol>
<li>Team get coordinated with each other</li>
<li>Everyone knows what amount of task has been done</li>
<li>Burndown chart gets more and more complete</li>
<li>Task board is updated </li>
<li>It doesn't last that much, 15 minutes won't kill anybody</li>
</ol>
Ho... | I had experience participating in a "SCRUM" team with several employers. It appears to me that the managers take out the "daily scrum meeting" as the main point of SCRUM, and set it as the goal, instead of having it for what it is: <strong>a mean to achieve more effective development cycle</strong>.
Very quickly the 1... | I would find daily stand up boring and useless if I felt there was little to no value in it. There are a few things that can reduce the utility of a daily standup.
<ul>
<li>The information being shared never pertains or affects me in any way.</li>
<li>Absence of team ownership and everyone always working on their own... | https://softwareengineering.stackexchange.com |
28,133 | [
"https://mechanics.stackexchange.com/questions/28133",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/7132/"
] | I flushed my transmission recently, and I overfilled it slightly, maybe by a 1/2 liter on a transmission that takes about 8 liters. When cold, the fluid is a little over the cold mark, but not up to the hot mark.
Will this harm the transmission?
| Automatic transmissions are very susceptible to damage from overfill. This occurs because auto transmission fluid expands a lot (well, a lot more than engine oil, for instance). The problem it can create is blowing the seals, like where the torque converter rides. The seal itself is not expensive in and of itself, but ... | I agree that overfilling transmission oil is not a good thing but how much overfilling would be more of a concern. I don't think the dipstick can gauge 100% accuracy, it's only a guide range. There has to be some small tolerance for error of over or under filling. I probably would be more concern with slightly under th... | https://mechanics.stackexchange.com |
286,036 | [
"https://softwareengineering.stackexchange.com/questions/286036",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/125105/"
] | I'm coding with a state pattern for an embedded device. I have a base/abstract class called State and then each discrete(concrete) state class implements the abstract State Class.
In the State Class I have several Abstract Methods. If I don't implement the abstract methods in the discrete(concrete) class, Visual Studi... | I guess the "correct" way to do this is to have a protected constructor on the base class which requires the state name as a parameter.
<pre><code>public abstract class State
{
private readonly string _name;
protected State(string name)
{
if(String.IsNullOrEmpty(name))
throw new Argume... | Your requirements are a contradiction:
<blockquote>
I'm trying to create a String property for <strong>each</strong> State called StateName.
</blockquote>
vs.
<blockquote>
But I <strong>don't need</strong> to implement all of that in <strong>each</strong> State.
</blockquote>
There's no language feature that a... | https://softwareengineering.stackexchange.com |
752,463 | [
"https://physics.stackexchange.com/questions/752463",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/359664/"
] | I understand that fire heats its surroundings via conduction, convection and radiation. I've read that conduction is nearly irrelevant to this process as air is a poor heat conductor. In descriptions of convection, people often just say <em>"fire heats the air and the air circulates heat to the environment"</... | Heat conductivity is not the same as the ability to absorb heat, only to pass the absorbed heat through the material. Air within the flame can absorb heat, but the air cannot quickly pass the heat to neighboring air molecules. This is partially due to the average distance between neighboring molecules within the air.... | Fire is a reaction that includes the air. To be precise, it includes a part of the air, oxygen. It releases the results of the reaction as a new part of the air. Those reaction results are hot and mix in with the rest of the surrounding air.
Air is a poor conductor when there is no ability to mix. The "output"... | https://physics.stackexchange.com |
374,414 | [
"https://mathoverflow.net/questions/374414",
"https://mathoverflow.net",
"https://mathoverflow.net/users/66131/"
] | The following sequence appears to be always an integer, experimentally.
<blockquote>
<strong>QUESTION.</strong> Let <span class="math-container">$n\in\mathbb{Z}^{+}$</span>. Are these indeed integers?
<span class="math-container">$$\sum_{k=1}^n\frac{(4k - 1)4^{2k - 1}\binom{2n}n^2}{k^2\binom{2k}k^2}.$$</span>
</blockqu... | <span class="math-container">$$\sum_{k=1}^n\frac{(4k - 1)4^{2k - 1}\binom{2n}n^2}{k^2\binom{2k}k^2}=16^n \left(1-\frac{\Gamma \left(n+\frac{1}{2}\right)^2}{\pi \Gamma (n+1)^2}\right)$$</span>
<span class="math-container">$$\qquad=2^{4n}-c_n^2,\;\;\text{with}\;\;c_n=2^n\frac{(2n-1)!!}{n!}={{2n}\choose n}. \qquad\qquad\... | Actually it is easy to give some other similar identities. For example,
<span class="math-container">$$\sum_{k=1}^n\frac{(9k-2)27^{k-1}\binom{2n}n\binom{3n}n}{k^2\binom{2k}k\binom{3k}k}=\frac{27^n}3-\binom{2n}n\binom{3n-1}{n-1}\in\mathbb Z.$$</span>
Also,
<span class="math-container">$$\sum_{k=1}^n\frac{(16k-3)64^{k-1}... | https://mathoverflow.net |
508,187 | [
"https://physics.stackexchange.com/questions/508187",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/144045/"
] | This is a formula I have seen stated in two different places in a relativistic context, but I do not know the proof and seem unable to derive it on my own. <span class="math-container">$E$</span> is the energy of a free particle, <span class="math-container">$v$</span> is its speed and <span class="math-container">$p$<... | The fundamental energy-momentum relation in special relativity is <span class="math-container">$E^2=p^2+m^2$</span> (let’s ignore factors of <span class="math-container">$c$</span>, since they will factor out in the end — that is, let’s work in natural units).
Taking the derivative with respect to <span class="math-co... | We have <span class="math-container">$E=\gamma mc^2$</span> (relativistic total energy) and <span class="math-container">$p=\gamma mv$</span>, where <span class="math-container">$\gamma=1/\sqrt{1-v^2/c^2}$</span>. Therefore, we can write:
<span class="math-container">$$E=\frac{pc^2}{v} \space,$$</span>
differentiati... | https://physics.stackexchange.com |
27,018 | [
"https://mechanics.stackexchange.com/questions/27018",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/15607/"
] | 4 weeks ago I changed a 12V battery on my Toyota Prius auto. But after being in for two weeks the battery was discharged again. I tried to recharge it, but it did not work - the charger does not start charging - though the battery voltage was 0.1 V. Now I want somehow to start the car and go to the service and check th... | IIRC, the Prius has a step down voltage regulator which charges the 12v battery from the main power. I'd bet this system is having an issue and is not charging the battery.
As for the 12v battery. I'd bet the old battery (the first replacement?) is good, but has dropped in voltage below what the charger can deal with... | Don't leave the proximity key anywhere near the vehicle. It wakes the computer which will slowly drain the battery.
| https://mechanics.stackexchange.com |
182,921 | [
"https://dba.stackexchange.com/questions/182921",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/132233/"
] | I will try to describe my problem as simple as I can.
I have a db with tables that contains columns with phone numbers ranges, e.g. <code>numbertype_id = 7</code>, <code>number_start = '00110000'</code>, <code>number_end = '00119999'</code>, <code>numbers = 10000</code> (of course I have an id pk and unique key index ... | Assumptions:
<ul>
<li>the query can only return 1 row (or none) and never 2 or more, i.e. the <code>(number_start, number_end)</code> ranges are not overlapping for the same <code>numbertype_id</code>.</li>
<li>the <code>number_start</code> and <code>number_end</code> values are all left-padded with 0s to the same le... | Providing a range in two columns leads to difficult-to-optimize queries.
Have both of these:
<pre><code>INDEX(numbertype_id, number_start)
INDEX(numbertype_id, number_end)
</code></pre>
Hopefully the Optimizer will pick the better of them.
If there is no need for <code>id</code>, get rid of it and promote your <cod... | https://dba.stackexchange.com |
177,124 | [
"https://mathoverflow.net/questions/177124",
"https://mathoverflow.net",
"https://mathoverflow.net/users/54610/"
] | <h1>Definitions and notations.</h1>
Let $\mathcal{P}(X)$ the <strong>power set</strong> of $X$.
Let $\tau_X\subseteq\mathcal{P}(X)$ a <strong>topology</strong> on X.
We call $A$ <strong>irreducible</strong> if every time $A=B\cup C$ with $B,C$ closed set then $(B=A)\vee(C=A)$.
We call $X$ <strong>sober</strong> if ... | A self-contained proof is in the book "Continuous lattices and domains" by G. Gierz, K. H. Hofmann, K. Keimel, J. D. Lawson, M. W. Mislove and D. S. Scott.
The particular place you need is Lemma II-1.19 on page 146.
| We have (only) to prove that for every open set <span class="math-container">$A\supseteq P$</span>, where <span class="math-container">$P=\bigcap F$</span>, we have <span class="math-container">$A\in F$</span> (for the whole notation you can see the question).
<h1>The missing step.</h1>
(we refer to [3], thanks to the ... | https://mathoverflow.net |
160,733 | [
"https://physics.stackexchange.com/questions/160733",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/25512/"
] | Let's say I have a rod of length $L$. The moment of inertia for spinning it around some point at a distance $d$ from one end can be calculated using the parallel axis theorem. Specifically, knowing that the moment of inertia when spun around its center is $\frac{1}{12}mL^2$, so the moment of inertia when spun around $d... | The parallel axis theorem only works when the initial moment is computed about an axis through the object's center of mass. It does not apply when the initial moment is computed about any arbitrary axis. That is, $I = I_{cm} + mr^2$, where $I_{cm}$ is the moment about an axis through the center of mass and $r$ is the... | I don't know the parallel axis, but here you have an extremely simple <strong>test</strong> whether your calculi are good or wrong. <em>It just completes the explanation given to you by pwf.</em>
The inertial momentum of a rod of uniform density \mu is
$I = \mu \int_{-d}^{L-d} l^2 dl = \mu \frac {(L-d)^3}{3} + \mu\fr... | https://physics.stackexchange.com |
530,389 | [
"https://electronics.stackexchange.com/questions/530389",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/69023/"
] | I'm working on a speaker project where I'd like to use a microcontroller's SPDIF output (aka IEC 60958) to drive audio data to a speaker.
I've' been doing research on the topic, and I'm having trouble grasping exactly what steps are required to convert the SPDIF data into an analog input signal for an audio amplifier.
... | The signal path outlined in the question is basically correct. Those are the necessary signal processing steps to get SPDIF audio to be output from a speaker.
In terms of a simplified approach, there are ICs which combine various pieces of the SPDIF signal path (e.g. DAC+amp), but these have various design tradeoffs t... | You need an audio DAC, one way or another. Either a device that can directly receive S/PDIF and output analog audio, in which case it might be a more complex audio codec chip, or simply an audio DAC which only has an I2S audio input, and then you only need an S/PDIF receiver which can output the audio data over I2S bus... | https://electronics.stackexchange.com |
286,932 | [
"https://stats.stackexchange.com/questions/286932",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/160443/"
] | I have 64 time meausures at morning, and 64 measures at evening.
I would like to use F-test, to compare variances of my times (are my times equally "stable" at morning an evening?). All time measures are made on me. F-test assumptions are, that samples are normally distributed and independent. I am little bit confus... | This is a matter of modeling. For most applications, we would model all data measured on the same individual as dependent. This dependency is often (mixed effect ANOVA models) modeled by some kind of "individual effect" that is somehow added to the independent time effects.
In your case, there is only one individual (... | Pitman's variance ratio test for correlated samples, may be good for you. It doesn't assume any dependency between samples. There is just a correction for correlation in test formula.
| https://stats.stackexchange.com |
126,807 | [
"https://stats.stackexchange.com/questions/126807",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/62176/"
] | If I have a population of 1948 students with a success rate of .154 (301 successes) and I break the 1948 students into their respective majors, how to I determine if the sub-population success rate is statistically significant?
For example, I have a sub-population of 188 students (from the 1948 above) and I know thei... | If what you have are truly populations and subpopulations, the word "significance" in the sense of "significance test" is meaningless. The purpose of signifcance testing is to make probability-based inference about unobservable population quantities on the basis that (say) the population was randomly sampled, or random... | If you only want to know if the proportion .2128 (40 / 188) differs from the value .154 (taken as set in stone), this is a simple binomial test. Here's an example in R:
<pre class="lang-r prettyprint-override"><code>binom.test(x=40, n=188, p=.154, alternative="greater")
# Exact binomial test
#
# data: 40 and 1... | https://stats.stackexchange.com |
339,187 | [
"https://softwareengineering.stackexchange.com/questions/339187",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/258213/"
] | I wrote a utils library (5 KLOC) that a lot of my projects use. I've also written a very small project (150 LOC) that needs just 1 or 2 of the classes in the utils library.
I really don't want to add such a large dependency for such a small use, but the other options...moving/copying the classes or having a utils2 lib... | The options are:
<ol>
<li>break your larger utility library in smaller libraries</li>
<li>use a larger library everywhere</li>
</ol>
There are pros and cons to each approach.
With 1., you end up having eventually a smaller effective installed component but you increase the level of coordination and you need more wor... | To the deployment, you can make build files that compiles only segments of your library. I made an ant build file that accomplish that by recieving a filter of packages and classes to include in the result and a location to drop the generated jar. In my case is Java specific, but this should be doable in many languages... | https://softwareengineering.stackexchange.com |
9,348 | [
"https://mechanics.stackexchange.com/questions/9348",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/-1/"
] | So Im still pretty new to driving stick. However even if I feather the clutch to get it rolling from a stop it always vibrates the car a little bit when I get close to the catch point. I've tried doing it SUPER slow and the car still vibrates a little bit, it's especially prevalent when going in reverse.
Is this norma... | It may be a case of the clutch still needing to be broke in and/or "bedded", but if it continues doing it after 500 to 1000 miles, I'd take it back to the dealership to have it looked over. You should not be causing any issues with the engine or the car, but that also depends on the level of vibration that you are feel... | practise makes perfect-it's a learning curve.Find a lonely road and persevere.you will
become so adept you could do it in your sleep
| https://mechanics.stackexchange.com |
1,033,790 | [
"https://math.stackexchange.com/questions/1033790",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/98214/"
] | Let us consider the following notations for $x \in X,y\in Y ,z \in Z$.
$$F(x,y,z)=x^yy^z$$
$$F_x(y,z)=x^yy^z$$
I am clear with former notation , but I saw latter one too , what's the difference between them ?
Is there any valid difference ?
If no difference then why multiple notations ?
| $F$ is a function of three variables ($x, y, z$). Whereas $F_{x}$ consists of two variables ($y, z$) and $x$ is fixed.
| There are many ways to write the evaluation of a univariate function:
<ul>
<li>$f(x)$ is the function $f$ evaluated at $x$</li>
<li>$fx$ is the function $f$ evaluated at $x$. Or occasionally the function $x$ evaluated at $f$</li>
<li>$a_n$ is the function $a$ evaluated at $n$. Usually $n$ is drawn from some interval o... | https://math.stackexchange.com |
4,224 | [
"https://mechanics.stackexchange.com/questions/4224",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2150/"
] | I recently went on a 10000k road trip, and accumulated a lot of insect remains on my vehicle. After several car washes, one of them that even included a bug spray before you entered the main wash, and doing some hand washing, there is still insect gunk on my vehicle! It's mostly on the bumper, the windshield was much... | There's a few methods, but remember, that if the bugs have been there for a while, the acidic content of the bugs might just have ruined the paint.
<ol>
<li>Use a light scouring pad, like a “000” steel wool, to slowly and carefully shave off layers of the bug.</li>
<li>Spray WD 40 on the bug, let sit for 10 to 15 min... | I have had very good luck with the type of kitchen sponge/scrubber made for teflon pans. It is wrapped in a nylon mesh that takes off bugs and pinesap but is gentle on the paint. Spray or wipe on any Bug and Tar remover from the auto parts store. Do small area at a time. Let it sit for 10-15 minutes in the shade befor... | https://mechanics.stackexchange.com |
146,319 | [
"https://chemistry.stackexchange.com/questions/146319",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/91758/"
] | From the definition of entropy change,
<span class="math-container">$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta Q}{T}\right )_{int.rev}$$</span>
From the closed system entropy balance, we have
<span class="math-container">$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta Q}{T}\right )_{b}+\sigma $$</span>
where <span class="... | The way that you describe it is exactly correct. This is the essence of the Clausius Inequality.
| When a system changes from state 1 to state 2, the change in entropy of the <em>system</em> is the same for all processes, because entropy is a state function.
The difference between a reversible and an irreversible process is that, in the latter case, there is net entropy production for the universe, i.e., for the sys... | https://chemistry.stackexchange.com |
53,758 | [
"https://chemistry.stackexchange.com/questions/53758",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/30035/"
] | I need to dry some solvents like $\text{MeOH, EtOH, and DMSO} $ and I have to take care of purity of the solvents. These solvents are HPLC grade.
I am interested in freezing point and boiling point of these solvents with <strong>maximum error of $ \pm 0.5 C$</strong>, hence, I do not prefer to add silica gel (or o... | There is actually a book on preparing laboratory chemicals you can look up:
<blockquote>
"Purification of Laboratory Chemicals" by WLF Armarego and CLL Chai
</blockquote>
However, given that all the chemicals you want to dry are extremely hygroscopic, I'm not sure how long they would stay super dry for calibration ... | I would suggest refractional destilation as a method to isolate your solvents from the impurities. You can also repeat this procedure until you have obtained a desired purity.
| https://chemistry.stackexchange.com |
3,653 | [
"https://dba.stackexchange.com/questions/3653",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/24/"
] | In a daily routine, I need to drop and do a bulk load of a database.
The problem is that I have a WebApp relying on that database. So I can't drop the database just like this.
What would be a good way to tackle this problem ?
| Well, this is straightforward in most databases. While your app is running, from your loading job:
<ol>
<li>Start a transaction (this may be implicit or may require a command, you don't specify which DB you are using)</li>
<li><code>DELETE</code> all the data from the tables (<em>not</em> drop or truncate)</li>
<li><c... | Do you need to drop and reload the database? In a case like yours, I would look at a way to synchronize the database with the reference set (the data you are loading).
An alternative approach would be to have two databases. Load a different one each day. Configure the webapp so that you can swap databases on the fl... | https://dba.stackexchange.com |
189,016 | [
"https://physics.stackexchange.com/questions/189016",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/83448/"
] | Has the frequency of CMBR changed at all since the beginning of the universe? Has it always had a microwave frequency or has the frequency increased/decreased over time or is the change due to factors such as the Red/Blue shift?
| No. Light travels at the speed of ... light, when measured locally in inertial reference frames. And the relationship between wavelength and frequency is $\lambda = c/f$.
As the universe expands, the wavelength of the cosmic microwave background photons is "stretched" and thus their frequency must decrease by the same... | Theoretically, the CMBR <em>is</em> what we see of the early visible universe. If we could be there to observe it, we might see much higher frequency radiation. However, due to the expansion of the universe, the wavelengths got stretched out and the frequency redshifted. Or perhaps you can say in our reference frame, w... | https://physics.stackexchange.com |
17,972 | [
"https://datascience.stackexchange.com/questions/17972",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/30539/"
] | Doing a logistic regression in R version 3.1.2 and I want to conduct a Hosmer Lemeshow test
<pre><code>model <- glm(y ~ a + b + c + d, data = data, family = binomial)
summary(model)
Call:
glm(formula = y ~ a + b + c + d, family = binomial,
data = data)
Deviance Residuals:
Min 1Q Median 3Q... | I think it could be that the model is being used and not the data, try:
hoslem.test(data$y, fitted(model), g = 10)
| It is possible that the vector "y" contains NA values or some vector that you used to define your default variable has NA values.
| https://datascience.stackexchange.com |
48,198 | [
"https://stats.stackexchange.com/questions/48198",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/1050/"
] | If have multivariate data of 3 response variables and 2 factors (f1 and f2). I can specify an linear model in different ways for this data, however I don't know what the difference between the models is.
Here is a plot of the data: the three variables (columns) and the 2 factors (rows and x-axis).
<pre><code>ggplot(d... | Question 1 - There are two differences between the two approaches.
First, by estimating it all together you are constraining the variance of the random part to be the same for each of variables 1, 2 and 5. If you fit the three models separately you will have a different estimate of the variance each time. A useful t... | I suggest that you use a model with a limited dependent variable. For example ordered probit, multinomial logit, negative binomial ...etc. The model choice depends on what you are modelling.
| https://stats.stackexchange.com |
650,407 | [
"https://math.stackexchange.com/questions/650407",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/38972/"
] | I'm reading text that states
<blockquote>
the vector $\ x \in \mathbb{R}^{n} $ is $\ s$-sparse if at most $\ s<n$ of its entries are non-zero
</blockquote>
Is that any different from stating:
<blockquote>
the vector $\ x$ is $\ s$-sparse if $\ s<n$ of its entries are non-zero.
</blockquote>
I don't see th... | Hint: integrate:<span class="math-container">$\;d(t) = \int v(t)\,dt$</span>
where <span class="math-container">$d(t)$</span> gives the distance traveled in <span class="math-container">$t$</span> seconds.
If you cannot use integration, graph the curve, <span class="math-container">$v(t)$</span> and try to approximate ... | Without using calculus:
Separate $v(t)$ into two components, its constant component, and its cosine component.
From the constant component, it's easy to start by observing that a constant speed of 20 ft/sec for 10 sec yields 200ft. Hang onto this number.
From the cosine component, we know that cosine has a period of... | https://math.stackexchange.com |
13,558 | [
"https://engineering.stackexchange.com/questions/13558",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/9839/"
] | Given an equation of motion of an undamped system $\mathbf{M}\mathbf{\ddot{q}} + \mathbf{K}\mathbf{q} = \mathbf{f}$, $\mathbf{M}$ indicates the mass-matrix, $\mathbf{K}$ the stiffness matrix, $\mathbf{q}$ the time-dependent displacement, and $\mathbf{f}$ the applied force. The roots, $\omega^2$, of the equation $det(\m... | Assume a 1d version of the equation. Then the K matrix becomes a <em>k</em>, spring constant.
In 1-D The equation reduces to : $m \ddot{q} + kq = f $
The q matrix also becomes x vector in one dimension. This is the differential equation for a forced mass-spring system. (@Jmac added the 1-d equation)
Similarly, The ... | The matrix $\mathbf{K}$ simply represents the force response to a unit displacement on each of the degrees of freedom of the system.
Consider a 2D cantilever beam of length $\ell$ with two degrees of freedom. The end displacement $\delta$ and the end slope $\theta$. You can assemble a stiffness matrix of the form $\ma... | https://engineering.stackexchange.com |
64,304 | [
"https://security.stackexchange.com/questions/64304",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/34161/"
] | A few years ago, there was a high-profile attack on a Wired editor, where the hackers added a credit card to the target's amazon account, then used that self-added credit card to gain access to the target's account. So they effectively poisoned Amazon's database for their attack, then social engineered their way throug... | The attack you describe happens because the user account is a container of credit cards, and Amazon equated "knowledge of a contained object" with "knowledge of the container". It's not surprising, because everyone assumes that a credit card must be kept secret, therefore knowledge of the credit card was evidence that... | There isn't really much you can do about the social engineering attacks apart from training you employees better who directly interact with the customers ( customer care reps) in this case. If they learn on how to ask more questions in case of suspicion, or update the whole security training program for them.
Again as... | https://security.stackexchange.com |
489,520 | [
"https://physics.stackexchange.com/questions/489520",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/220348/"
] | I have been given this<span class="math-container">$$
\delta X^{\mu}=\omega_{\mu \nu}\left(M^{\mu \mu}\right)_{\sigma}^{\rho} X^{\sigma}
$$</span>
and I think it should be equal to this but I'm confused if I'm doing it correctly
<span class="math-container">$$
\delta X^{\mu}=\omega_{\sigma}^{\rho} X^{\sigma}
$$</span... | <span class="math-container">$M$</span> here represents the generators of the vector representation of the Lorentz group, and <span class="math-container">$\omega$</span> is an antisymmetric tensor parametrizing the group elements. In terms of these generators, a Lorentz group element in the vector representation is gi... | Well, there's a problem in your first formula because as far as <em>Einstein's Summation Convention</em> is concerned the symbol:
<span class="math-container">$$ \omega_{\mu\nu}M^{\mu\mu}$$</span>
is totaly meaningless, because you have sum only with two repeated indices.
Also, poincaré transformations are, in fact,... | https://physics.stackexchange.com |
108,562 | [
"https://dba.stackexchange.com/questions/108562",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/24418/"
] | Well, the title of the question is self-explanatory.
<ul>
<li>Export finished successfully <strong>with warnings</strong>.</li>
<li>Log shows several ORA-01555 snapshot too old errors.</li>
</ul>
<strong>- Is it OK to use that dmp file to perform an import full in another instance?</strong>
<strong>- Would running t... | It would be time saving if you just backup the tables being errored in ORA-1555 after the warning full backups.
Yes, to answer main question, it is good backup to be imported, you can exclude the errored tables or use table_exists_action=replace using tables only backup after taking the tables backup in above para. ... | Technically, you could, but it is <strong>incomplete</strong>, so better repeat the export after performing the necessary actions to avoid ORA-01555 errors (have an appropriately sized undo tablespace, set <code>undo_retention</code> and <code>retention guarantee</code>).
| https://dba.stackexchange.com |
409,448 | [
"https://softwareengineering.stackexchange.com/questions/409448",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/223337/"
] | I'm not sure if this is the adequate site (maybe CodeReview?) but it's the only one here in StackExchange that have got a "clean code" tag ... There is no need for downvotes if this is not the correct place just inform me in the comments and I will move it.
I've got this piece of java code
<pre><code> private void ex... | My opinion is this question would be better suited on Code Review but, anyway, here is what I would do.
The nested ifs of your first code are really ugly, and they will become even worse if, in the future, you won't have 4 steps but 10.
You could try this:
<pre><code>private void executeCommand() {
if (!executeP... | Early return is the most useful solution, but if you must not use them, then you could do:
<pre><code> private void executeCommand() {
boolean bOK = true;
if (bOK) {
bOK = executePart1();
if (!bOK) {
// error handling
}
}
if (bOK) {
bOK = executePart2();
if (!bOK... | https://softwareengineering.stackexchange.com |
28,922 | [
"https://physics.stackexchange.com/questions/28922",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/4/"
] | If an object is acted on by equal and opposite forces then it will be in equilibrium, and it's acceleration or velocity (and so direction as well) will not be changed.
So when a ball bounces, it exerts a force on the floor, which matches the magnitude of the force in the opposite direction (the ball is bouncing perfec... | You've misunderstood the statement.
When A exerts $\vec{F}_{A \to B}$ on B, B exerts an equal and opposite force $\vec{F}_{B \to A} = - \vec{F}_{A \to B}$ on A.
The only forces acting on the ball a gravity and the normal force, <em>and</em> the floor experiences a force from the ball which is equal in magnitude and o... | The easiest way to understand this is by flows of momentum, the ball has momentum down, and when it hits the floor, it transfers twice this amount of down momentum to the floor, and so is left with negative this much down-momentum, which is up-momentum.
The statement of Newton's laws are nothing more than the flows of... | https://physics.stackexchange.com |
102,632 | [
"https://stats.stackexchange.com/questions/102632",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/46504/"
] | I am learning ML. I have encountered a lot probability density functions. I want to use MATLAB to illustrate them. For example,the density function of the Normal distribution function in two dimensions:
$$p(\vec{x};\mu,\Sigma) = \frac{1}{2\pi \sqrt{\det(\Sigma)}}\exp\left(-\frac{1}{2}(\vec{x}-\mu)^T\Sigma^{-1}(\vec{x}... | It is not terribly enlightening, I am afraid, but you can permute the parallel dimensions out to the third and fourth, use <code>bsxfun</code> to do the broadcasting, then bring the results back. It involves a few <code>shiftdim</code> operations:
<pre><code>% set the random seed:
randn('state',[2979743726;1541610269]... | To do that operation I would try something along the lines of
<pre><code>product = [X(:), Y(:)] * ( SigmaInv * [X(:)'; Y(:)'] )';
</code></pre>
where <code>SigmaInv</code> is your 2x2 matrix. The variable <code>product</code> should be a matrix having the values for all the points of the grid.
| https://stats.stackexchange.com |
263,726 | [
"https://softwareengineering.stackexchange.com/questions/263726",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/108835/"
] | Consider an e-commerce site, where Alice and Bob are both editing the product listings. Alice is improving descriptions, while Bob is updating prices. They start editing the Acme Wonder Widget at the same time. Bob finishes first and saves the product with the new price. Alice takes a bit longer to update the descripti... | You need to "read your writes", which means before you write down a change, you need to read the record again and check if any changes where made to it since you last read it. You can do this field-by-field (fine-grained) or based on a timestamp (coarse-grained). While you do this check you need an exclusive lock on th... | I have seen 2 main ways:
<ol>
<li>Add the timestamp of the last update of the page the use is editing in a hidden input. When committing the timestamp is checked against the current one and if they don't match it has been updated by someone else and return an error.
<ul>
<li>pro: multiple users can edit different par... | https://softwareengineering.stackexchange.com |
218,202 | [
"https://math.stackexchange.com/questions/218202",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/45526/"
] | Given the series:
$$\sqrt c + \sqrt{c\sqrt c} + \sqrt{c\sqrt{c\sqrt c}} + \ldots$$
where $0 < c < 1$
What is the general term of this series?
| $a_1 = \sqrt{c} = c^{1/2}$, $a_2 = \sqrt{c\sqrt{c}} = \sqrt{c^{3/2}} = c^{3/4}$, $a_3 = \sqrt{c\sqrt{c\sqrt{c}}} = \sqrt{c \times c^{3/4}} = c^{7/4}$. In general, $$a_{n+1} = \sqrt{c a_{n-1}}$$ with $a_0 = 1$.
This gives us
$a_n = c^{1-1/2^n}$
| Each term can be written as $a_n = a_{n-1}c^{2^{-n}}$. Since $a_1 = c^{1/2}$, this gives
$$a_n = c^{\;\sum\limits_{k=1}^n 2^{-k}} = c^{1-2^{-n}}$$
| https://math.stackexchange.com |
277,761 | [
"https://stats.stackexchange.com/questions/277761",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/160219/"
] | I am trying to conduct a research on brand preferences and I am trying to analyze regression equation i.e. which factors affects the consumer preferences (dependent factor) and other determined factors (independent variable). So my question is how to design a questionnaire to calculate the linear regression among these... | The most powerful test is always the best test provided it is of correct size. I do not think you have evaluated the size of your test under simulation. Generate data according to the null hypothesis and evaluate the frequency with which the null hypothesis rejects the null. It should be exactly 0.05. If it is under 0.... | In the absence of a specific loss function, that is hard to say. If the other test has higher type I error rate and lower type II error rate (i.e., higher power), the answer boils down to whether you consider a type I or a type II error to be more consequential.
| https://stats.stackexchange.com |
11,919 | [
"https://electronics.stackexchange.com/questions/11919",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/3075/"
] | I just built a small 5.1V regulator with LM317, using 220 and 680 ohm resistors. However, I measure 8.6V at the output without a load connected. Is this normal, i.e. under a load (about 120 ohm) it would drop to 5.1V? The input is a 9V/300mA unregulated wall wart, which reads about 13V without a load.
| You need a minimum load of 10mA for it to be stable. A tip is to add a LED and run it on 5mA. You'll know whether the supply is on, and it will add additional load to make it stable.
Note that the adjustment resistors of 220+680 ohm also give some load, of about 5.6mA. Together with a LED you get more than the requir... | One way to ensure a minimum load is to make sure the feedback network draws the minimum load. For example 240 ohms and 75 ohms gives a 5.25V output and draws 16mA. Tweak the resistors to get it perfect.
| https://electronics.stackexchange.com |
1,479,817 | [
"https://math.stackexchange.com/questions/1479817",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/37244/"
] | If $b_j>0$ and $\sum b_j$ converges then show that
$\sum(b_j)^\frac{1}{2}\frac{1}{j^a}$ converges for any
$a>\frac{1}{2}$
My suggestion is that if a is 1/2 or less then you get
$\sum \frac{b_j^{1/2}}{j^{1/2}}$
then you get get
$\sum {b_j}/{j}$
$b_j\sum{\frac{1}{j}}$ diverge by p series.
| Apply the Cauchy-Schwarz inequality to the partial sums:
$$ \sum_{j=0}^n \frac{b_j^{1/2}}{j^{\alpha}} \leqslant \sqrt{\sum_{j=0}^n \frac{1}{j^{2\alpha}}} \sqrt{ \sum_{j=0}^n b_j}. $$
Taking the limit as $n \to \infty$, the first multiplicand is bounded above since the series $\sum_{j} j^{-k}$ converges for $k>1$ by ... | Hint: By the Cauchy-Schwarz inequality, you have
$$ \sum_{j = 1}^{N} \sqrt{b_j} \frac{1}{j^a} \leq \left( \sum_{j=1}^N b_j \right)^{\frac{1}{2}} \left( \sum_{j=1}^N \frac{1}{j^{2a}} \right)^{\frac{1}{2}}. $$
| https://math.stackexchange.com |
350,361 | [
"https://math.stackexchange.com/questions/350361",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/70169/"
] | <blockquote>
Solve $z^5 + 16\bar z = 0$ for $z\in \mathbb{C}$.
</blockquote>
Need some help figuring out this problem.
| We have
$$z^5 + 16 \overline{z}=0 \iff z^5=-16\cdot \overline{z}$$
We use $z=|z|\cdot \exp(i\varphi)$
$$|z|^5 \exp(5i \varphi)= -16 |z|\exp(-i \varphi)$$
Now use that
$$-1=\exp(i\pi)$$
Hence
$$|z|^5 \exp(5 i \varphi) = 16 |z| \exp(i(\varphi+\pi))$$
Here we see that $z=0$ is a solution, now we search other solutions.
... | Here is a hint. $z^5 = -16 \overline{z}$. Hence $|z|^5 = 16 |z|$, from which we see that either $z=0$ or $|z| = 2$.
Then I would multiply across by $z$ to get $z^6 = -16 |z|^2 = -64$ (ignoring the zero solution, of course).
| https://math.stackexchange.com |
300,308 | [
"https://softwareengineering.stackexchange.com/questions/300308",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/200891/"
] | Background:
My bosses want to merge two application that have two separate purposes.
<ul>
<li>One being for monitoring of equipment and bandwidth for our internal
network operations.</li>
<li>The other is an application to view similar data just less granular
and with less detail. This second application has to also p... | I see two distinct questions here:
<ol>
<li>Does the combined functionality make sense?</li>
<li>Does the work of converting the two applications to one pass a cost/benefit analysis?</li>
</ol>
The first question should be purely user-driven. Does it make sense for users to have these two sets of functions together?... | My view is that this comes down to your definition of 'Application'
Lets say you have the following n-tier structure
<ul>
<li>Database A</li>
<li>Database B</li>
<li>Web Service A</li>
<li>Web Service B </li>
<li>Application C</li>
</ul>
Where A is your client facing stuff and B is the low level monitoring.
So we a... | https://softwareengineering.stackexchange.com |
558,666 | [
"https://electronics.stackexchange.com/questions/558666",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/224636/"
] | There are two battery operated devices connected to the garage door in my house. One is a bought solution which opens/closes the garage door, the other is a self-made module which detects whether or not the garage door is open, and communicates this with a receiver in the house.
Both are running on batteries, and both ... | Use a 12 volt adapter and check that it works exclusively on the device that needs 12 volts before trying to work a dual solution. Once you are happy with that, get an isolating DC-to-DC converter such as 12 volts to 12 volts or 12 volts to 9 volts and connect that to the output of the 12 volt adapter. Make sure the sy... | It's easier to step voltage down than to step it up. So a good starting point would be an off-the-shelf 12V power supply.
Then to give the 3.2V supply, use an off-the-shelf DC/DC converter, or make up a simple linear voltage regulator. Anything that runs off a coin cell only needs a tiny current, so there's no need t... | https://electronics.stackexchange.com |
223,394 | [
"https://dba.stackexchange.com/questions/223394",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/-1/"
] | <pre><code> SELECT DISTINCT re.*
FROM `reports` r
LEFT JOIN `users` u
ON u.`id_rep` = r.`id`
JOIN `customers` c
ON u.`id` = r.`uid`
WHERE r.`uid` = '1' and r.`name` LIKE 'urgent'
ORDER BY r.date DESC
</code></pre>
Without making any modifications prior to the WHERE clause, would it be po... | <blockquote>
That is, when table row is deleted, it's PK must be reused in subsequent inserts.
</blockquote>
What universe is your lecturer from??
That is grossly inefficient. If you try to do that, you will cut your performance prospects down by a factor of 10.
If you need gapless numbers for auditing reasons, b... | The reuse of PK id values has problems and generally should be avoided.
First, the implementation of auto_increment columns doesn't provide the guarantee of being gapless. Indeed gaps will occur if you rollback an insert on an auto increment column.
Secondly the gap ID may refer to existing data that hasn't been dele... | https://dba.stackexchange.com |
3,969,557 | [
"https://math.stackexchange.com/questions/3969557",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/477532/"
] | I would like to know why the inequality (6.26 in the below pasted solution) <span class="math-container">$f(k+1) \leq \int_k^{k+1} f(x) \, dx \leq f(k)$</span> is true. It feels true intuitively since <span class="math-container">$f$</span> is a mono decreasing function and the segment length is <span class="math-conta... | <span class="math-container">$f(k+1)$</span> is a constant not a function, and <span class="math-container">$f(k+1) \leq f(x)$</span> meaning <span class="math-container">$f(k+1)(k+1 -k) = f(k+1) = \int_{k}^{k+1}f(k+1) \leq \int_{k}^{k+1}f(x)$</span>. The other inequality is the same.
| The mean value theorem for integrals implies (for <span class="math-container">$f$</span> continuous on <span class="math-container">$[a,b]$</span>) that <span class="math-container">$\int_a^b f(t)dt=(b-a)f(c)$</span> for some <span class="math-container">$c \in [a,b].$</span> Replace <span class="math-container">$a$</... | https://math.stackexchange.com |
2,582,986 | [
"https://math.stackexchange.com/questions/2582986",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/479883/"
] | I am learning about modular equations. In my math textbook it says "For the diophantine equation $ax + by = c$, $a, b, c \neq 0$. To find which integers $x$ and $y$ satisfy the equation, the equality can be reformulated to a congruence: Determine $x$ so that $ax \equiv c$ (mod $b$)."
I don't see why it is possible to... | If $ax \equiv c \pmod b$, it must mean that $ax-c$ is divisible by $b$, so that:
$$ax - c = kb \implies ax-kb = c$$
And if $ax+by=c$, then obviously $ax \equiv c \pmod b$, so the equations are equivalent.
| This answer serves as a summary and elaboration of Elie Louis answer.
$$\eqalign{
& ax \equiv c\left( {\bmod b} \right) \Leftrightarrow ax\bmod b = c\bmod b \cr
& ax = pb + r{\rm{ }} \wedge {\rm{ }}c = qb + r \cr
& ax - c = pb + r - qb - r = pb - qb = b(p - q) = kb,{\rm{ }}k = p - q \Rightarrow b... | https://math.stackexchange.com |
220,019 | [
"https://security.stackexchange.com/questions/220019",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/220305/"
] | When using a single page application, in what way is access token + refresh token more secure than a single token in a cookie with SameSite: strict.
Given the browser supports SameSite.
I completely understand that if you don't have the SameSite setting available that you need an access token and a refresh token.
It ju... | <h1>Simplification</h1>
Neither option is remotely secure. But you present those as THE options, so I'll address them first, then present you an option 3.
<h1>Security: Technical</h1>
Given your two options, neither is technically superior. The addition of SSL/TLS would only be security theater.
In regards to you... | I'm coming from the assumption that you don't leave any backdoor open in either of the methods, and choose high-entropy passwords for Basic Auth. In that case, the biggest difference between the methods is that HTTPS will encrypt the traffic and prevent Man-in-the-Middle Attacks, making it impossible for anyone to eave... | https://security.stackexchange.com |
546,026 | [
"https://physics.stackexchange.com/questions/546026",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/261792/"
] | In a question on the difference between the 1st and 2nd order maxima formed when light of 2 different Wavelengths is incident on a diffraction grating, the marking scheme mentions that separation of the maxima of the wavelength increases with n, with the reason that <span class="math-container">$\Delta \theta$</span> ... | The concept which you have got wrong is that of gravitational potential energy.<br>
A system of one mass on its own cannot have gravitational potential energy.<br>
Your second misconception is the distance moved by each mass relative to the centre of mass of the two mass system.
The use of gravitational potential wi... | You assumed that one of the bodies is at rest (since you only have one term for kinetic energy) but both of the bodies are moving toward each other and they gain equal amounts of energy (by symmetry of the system).So you must take 2 terms of kinetic energy, one for each star.
| https://physics.stackexchange.com |
415,806 | [
"https://mathoverflow.net/questions/415806",
"https://mathoverflow.net",
"https://mathoverflow.net/users/174600/"
] | I'm trying to calculate the weak limit of <span class="math-container">$\mathcal{E}_N(x)=\sum_{k=1}^{2^N}\delta_{x-Z_k}$</span> , with <span class="math-container">$Z_k=X_k-\max_{k\leq 2^N}X_k$</span>, <span class="math-container">$\{X_k\}$</span> being <span class="math-container">$2^N$</span> copies of i.i.d. Gaussia... | <span class="math-container">$\newcommand\R{\mathbb R}\newcommand{\ep}{\varepsilon}\newcommand{\de}{\delta}\newcommand{\vpi}{\varphi}$</span>For <span class="math-container">$\phi=c\,1_{[-A,\infty)}$</span> with <span class="math-container">$c\ge0$</span> and <span class="math-container">$A\ge0$</span>, the expectation... | I just found another way of representing this in terms of Poisson Point Process.
To simplify the notation we assume now the number of i.i.d. Gaussians are <span class="math-container">$e^t$</span> and have distribution <span class="math-container">$N(0,t)$</span>. Then the approach suggested by @Iosif Pinelis will give... | https://mathoverflow.net |
33,309 | [
"https://mechanics.stackexchange.com/questions/33309",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/20032/"
] | I have a project to replace my car's instrument panel with a Android tablet. So I'm developing an application that communicates with an ELM327 device through bluetooth. I have managed to successfully get things like engine RPM, speed and temperature through OBD II, what I can't figure out is how to get some specific in... | Start off with a copy of the service manual for your car. The electrical schematics will help you understand where the various annunciators come from. Earlier cars typically have less data available via ODB II (whose original intent was to provide a way to monitor pollution controls).
If you add something like a Raspb... | You will not be able to read everything using OBD. Sometimes you can be lucky and the proprietary protocol your car uses can provide you with the right info, however this wouldn't be reliable as it will be considered a diagnostic session by the car's computers (and you may not be able to talk to two computers at once).... | https://mechanics.stackexchange.com |
90,137 | [
"https://dba.stackexchange.com/questions/90137",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/8830/"
] | I'm looking for a specific "best practice" or "pattern" concerning entities that are shared between different entities, having a relation to one of many.
For example, one may have the generic entity "Address", which could be used to store the common address fields for customers, suppliers, employees, etc...
Would a s... | I can't point to anything authoritative, but if you think through the details of such an implementation, the potential down sides are evident.
Having a "shared" <em>subsidiary</em> table is problematic primarily because if two "parent" tables (say, <code>Customer</code> and <code>Employee</code>) both utilize the same... | The motivation for piling every kind of address into a single table is usually a misinterpretation and misapplication of the notion of code reuse.
People can make the mistake of assuming that because you have two entities with some common set of attributes, that those attributes belong in their own table. Sometimes... | https://dba.stackexchange.com |
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