text stringlengths 1 1.11k | source dict |
|---|---|
newtonian-mechanics, forces, momentum, conservation-laws
Which is a consequence of which? Will it be right to treat one as a consequence of the other? As far as the actual physics is concerned, it is meaningless to talk of whether conservation of momentum is "more fundamental" than Newton's third law -- you can axiomatise classical physics in either way -- from Newton's laws, from conservation laws, from symmetry laws, from an action principle, whatever. You can prove the resulting theories are equivalent, in the sense that all the alternative axiomatic systems imply each other.
In terms of understanding, it makes sense to have multiple different frameworks in your head -- a symmetry-based framework is really good intuitively, especially once you understand Noether's theorem, while an action principle is the most powerful and also more useful when you leave the realm of classical physics. Treating Newton's laws as axioms isn't a great idea -- it's mostly just historically relevant. | {
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• I just found this comment: math.stackexchange.com/a/1309973/481197 I now know it. but is it necessary in this proof? – user481197 Jan 13 '18 at 13:13
• Hello @AbdukMalekAltawekji. In this case the overline is used to denote that the $a_0a_1a_2\cdots a_{n- 1}$ term denotes a number with $n$ digits, as opposed to a product. Normally when variables are written next to each other, it means they are multiplied together. In this case the overline is used to clarify that it's not $a_0 \cdot a_1 \cdot a_2 \cdots a_3$. In the other answer you linked, the overline is after a decimal point, and indicates a repeating decimal. – Zubin Mukerjee Jan 14 '18 at 1:38 | {
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"openwebmath_score": 0.8290954828262329,
"tags": null,
"url": "https://math.stackexchange.com/questions/341202/how-to-prove-the-divisibility-rule-for-3"
} |
thermodynamics
Image from Engineering toolbox article on Convective Heat Transfer
The curve at very low air speeds depends on many factors like surface texture - but the trend clearly shows that "faster air flow leads to faster heat transfer".
For evaporation, the situation is a bit more complex still. Evaporating water actually "draws heat" from the surface. This is because not all molecules move at the same speed - and it's the fastest molecules that have the best chance of escaping. When the smartest person leaves the room, the average IQ in the room goes down a bit; when the hottest molecule in the liquid leaves, the rest of the liquid becomes a little bit colder. | {
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"url": null
} |
reproduction, life
My opinion on your definition
Personally, I am not a big fan of your definition but again it is nothing but a matter of preferences. I don't like that your definition is unclear because there are plenty of limit cases and because there are plenty of cases we would want to call alive that we can't anymore (like a woman after menopause for example!) Every definition of life would eave limit cases but with your definition, it really easy to find these limit cases.
Is this question about Biology?
No, it is not. It is a question of philosophy.
Other interesting post on Biology.Stack
You might want to have a look at why isn't a virus alive. | {
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python, object-oriented, server, chat
for channel in client.channels:
if channel in clnt.channels:
client.connection.send(msg)
break
def _channel_broadcast(self, conn, chan, msg):
for client in self._clients.values():
if client.nick == self._clients[conn].nick:
continue
if chan in client.channels:
client.send(msg)
def _nick_in_use(self, nick):
"""
:param nick: Nickname of client
:type nick: str
:return: True if a client with that name exists, else False
"""
for client in self._clients.values():
if client.nick == nick:
return True
else:
return False
def _valid_nick(self, nick):
if not all(c in ALLOWED_NICKNAME for c in nick) or len(nick) > 9 or\
not len(nick):
return False
return True | {
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"tags": "python, object-oriented, server, chat",
"url": null
} |
c#, performance, parsing, regex
featureName = command[2].Substring(0, command[2].IndexOf('[')).ToUpper(); //everything before the bracket is the name of the object
}
catch (Exception ex)
{
return;
}
if (!double.TryParse(command[3], out double longitude) || !double.TryParse(command[4], out double latitude))
{
return;
}
try
{
BaseShape shape; | {
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} |
optics, diffraction
1) E. Marchand & E. Wolf, Consistent formulation of the Rayleigh-Kirchhoff diffraction theory , Journal of Optical society of America, Volume 56, Number 12., December, 1966. | {
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deep-learning, philosophy, agi
Finally, we might say that an entity "understands" a concept if it can generate examples of it. For example, I can generate examples of problems in arithmetic, and their solutions. Under this definition, I probably do not "understand" infinity, because I cannot actually point to or create any concrete thing in the real world that is definitely infinite. I cannot, for instance, actually write down an infinitely long list of numbers, merely formulas that express ways to create ever longer lists by investing ever more effort in writing them out. A computer ought to be at least as good as me at this. This definition also does not work.
This is not an exhaustive list of possible definitions of "understands", but we have covered "understands" as I understand it pretty well. Under every definition of understanding, there isn't anything special about infinity that separates it from other mathematical concepts. | {
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thermodynamics
Update:
Because in chemistry we learned about solubility and diffusion, so what about an osmotic pressure power plant, which turned out that there were some exploiting sea/river gradient. But I was more interested in the fact that solubility increased with temperature and I found that Na2SO4 has an interesting temperature/solubility curve. So that should exert ~70 bar of pressure at 50% solution at 40 ℃. Then I would cool it down to ~0 ℃ so that the solid Na2SO4 dives down and the less dense nearly just water (which gained its potential energy by the osmotic pressure) can be used in a turbine to generate energy and then fall back to the 40℃ container from which the diffusion occurs to the Na2SO4 solution.
It looks that there is the problem with the efficiency because heating the cooled water takes tens times more energy (did I count right?). | {
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javascript, jquery, html, css, html5
#menu {
position: relative;
display: inline-block;
overflow: hidden;
text-align: center;
width: 250px;
}
#menu span, #menu a {
display: inline-block;
font-size: 30px;
white-space: nowrap;
transition: transform .5s ease-out, opacity .5s;
}
#menu a {
position: absolute;
left: 100%; top: 0;
width: 33.33%;
}
#menu:hover a:nth-child(2) { transform:translateX(-300%); }
#menu:hover a:nth-child(3) { transform:translateX(-200%); }
#menu:hover a:nth-child(4) { transform:translateX(-100%); }
#menu:hover span{
transform:translateX(-50%);
opacity:0;
}
<body>
<nav id="menu">
<span>Hover for items!</span>
<a href="#1">Item 1</a>
<a href="#2">Item 2</a>
<a href="#3">Item 3</a>
</nav>
</body>
Browser support (with appropriate prefixes):
transitions : IE10+ (canIuse)
2D transforms : IE9+ (canIuse)
nth-child() selector : IE9+ (canIuse) | {
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Well, so we did have a formula for last time for the change in the inverse matrix. And I didn't get every u and v transpose in the right place in the video or in the first version of the notes, but I hope that that formula, that that Woodbury Morrison formula will be correct this time. So I won't go back over that part.
But I realize also there is another question that we can answer when the change is very small, when the change in A is dA or delta A, a small change. And that's, of course, what calculus is about. So I have to sort of parallel topics here. What is the derivative when the change is infinitesimal? And what is the actual change when the change is finite size? | {
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physical-chemistry, thermodynamics, pressure
Classical Thermodynamics
[OP] I've come across this article which says that the constant pressure heat capacity is independent of pressure.
First you need to accept the ideal gas law, that comes from early experimentation by well-known chemists
$$ pV = RT \tag{3} $$
$V$ here is the molar volume.
In addition you need to accept some consequences that derive from Joule's experiments, which he carried out in his basement in Manchester. If you are interested in, you can search them, they were very basic but accurate. One of these consequences is the following:
The internal energy of an ideal gas is only a function of temperature, i.e., $ U = U(T)$. | {
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algorithms, control-systems, adaptive-algorithms, dynamic-programming
For example for a problem with no inequality constraints and only linear equality constraints, such that,
$$
x(k+1+i) = A\, x(k+i) + B\, u(k+i) \qquad \forall\ i = 0, \ldots, N , \tag{3}
$$
with $x(k) = x_0$, you can find all other $N$ states of the system as a function of $\textbf{u}$ with,
$$
\begin{bmatrix}
x(k+1) \\ x(k+2) \\ \vdots \\ x(k+N)
\end{bmatrix} = \underbrace{\begin{bmatrix}
A \\ A^2 \\ \vdots \\ A^N
\end{bmatrix}}_{\textbf{A}} x_0 + \underbrace{\begin{bmatrix}
B & 0 & \cdots & 0 \\
AB & B & \cdots & 0 \\
\vdots & \vdots & \ddots \\
A^{N-1}B & A^{N-2}B & \cdots & B
\end{bmatrix}}_{\textbf{B}} \textbf{u}. \tag{4}
$$
The cost function from equation $(1)$, denoted as $J(k)$ in your linked paper, can then also be written as,
$$
J(k) = \left[\textbf{A} x_0\! + \textbf{B} \textbf{u}\right]^T\! \underbrace{\begin{bmatrix}
Q & 0 & \cdots & 0 \\
0 & Q & & \vdots \\
\vdots & & \ddots & 0 \\
0 & \cdots & 0 & Q | {
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reference-request, formal-methods, proof-assistants, model-checking
Principles of Model Checking by Baier and Katoen contains a lot of examples and pretty detailed algorithmic description.
The SPIN Model Checker by Gerard Holzmann is a very different treatment from the author of one of the earliest model checkers. He has maintained the tool for about thirty years and has a "programmatic" approach.
A better bet may be to follow the course notes and lab assignments of some courses available online. At least you will find the theory, practice and examples, even though they are not organised in a book.
Edmund Clarke's course in CMU has a reading list which includes tutorials for a few different model checkers.
Joost-Pieter Katoen's software verification course and the followup on Practical Model Checking and Advanced Model Checking cover a lot of ground. | {
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gradient-descent, bayesian, mini-batch-gradient-descent, sgd
The final "best approach" is usually problem specific - small batch sizes might not work for GAN type models, and large batch sizes might be slow and sub-optimal for certain vision based tasks.
Friends don't let friends use large batch sizes
There is literature to support usage of small batch sizes at almost all times. Even though this idea was supported by Yann Lecun, there are differences of opinion.
Super convergence
There are also other tricks that you might consider, if you are interested in faster convergence, playing with learning rate cycling. | {
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algorithms, subsequences
If we are only allowed comparisons, then we can get an $\Omega(n\log n)$ lower bound from Element Distinctness. Suppose that we could solve our problem using $T(n)$ comparisons. Given a sequence $a_1,\ldots,a_n$, consider the sequence $a_1,\ldots,a_n,a_1,\ldots,a_n$. If all elements are distinct, the shortest subsequence containing all elements has length $n$. Otherwise, if $a_i = a_j$ for $i < j$ then the subsequence $a_{i+1},\ldots,a_n,a_1,\ldots,a_{i-1}$ contains all elements and has length $n-1$. This shows that we can solve Element Distinctness in time $T(2n)$. The well-known lower bound $\Omega(n\log n)$ on Element Distinctness implies that $T(2n) = \Omega(n\log n)$, and so our algorithm is optimal. (Formally speaking, we also need to handle odd input lengths. We can do this by adding a fresh element between the two copies of the original sequence.) | {
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php, algorithm, html
Title: Dynamic two-column list, "Vertical Wrap" I have created a very simple script that will create two columns which are populated by an array. It works, but I am certain that the way that I have gone about it is not the best way. I have been searching for simple, sample scripts which would aide me in understanding how to best approach this, but all of them have been too specific to their application.
This is what I have made:
$assets = array('Bag', 'Charger', 'Power Cable', 'Video Cable',
'Mouse', 'Keyboard', 'Test', 'Test 2', 'Test 3');
$assets_count = count($assets);
$halfway_raw = $assets_count / 2;
$halfway = round($halfway_raw, 0) - 1;
echo '<ul class="col-1">';
for($i = 0; $i < $assets_count; $i++) {
if($i == $halfway) {
echo '<li>' . $assets[$i] . '</li>';
echo '</ul>';
echo '<ul class="col-2">';
} else {
echo '<li>' . $assets[$i] . '</li>';
}
}
echo '</ul>'; | {
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"tags": "php, algorithm, html",
"url": null
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# Math Help - Chinese Remainder Theorem
1. ## Chinese Remainder Theorem
have a problem on hand - this one is kinda easy- but am stuck :P
the problem is :
Solve using CRT:
x congruent to 8(mod13)
x congruent to 1(mod 5)
x congruent to 5 (mod 6)
i have gotten most of it. just want to be sure
thanks
2. Originally Posted by darren_a1
have a problem on hand - this one is kinda easy- but am stuck :P
the problem is :
Solve using CRT:
x congruent to 8(mod13)
x congruent to 1(mod 5)
x congruent to 5 (mod 6)
i have gotten most of it. just want to be sure | {
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for the book The Elements of Statistical Learning , chapter 3 # Data was described on page 3. Ridge regression is a way to create a parsimonious model when the number of predictor variables in a set exceeds the number of observations, or when a data set has multicollinearity (correlations between predictor variables). Ridge regression is a kind of shrinkage, so called because it reduces the components. welcome to my blog: yanke23. Maybe I don't understand enough about ridge regression generally or maybe the coefficients coming from b_ridge_matlab = ridge(y,XX,lambda,0) are to be used with some special prediction routine and not just y_ridge_matlab = X*b_ridge_matlab;. RegressionLinear is a trained linear model object for regression; the linear model is a support vector machine regression (SVM) or linear regression model. ¦ ¦ m i i i m i y i y i y b 1 2 1 min ( Ö ) ( ( w x )). 2 Ridge Regression Solution to the ℓ2 problem Data Augmentation Approach Bayesian Interpretation The SVD and | {
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"lm_q1q2_score": 0.8286972025316494,
"lm_q2_score": 0.837619959279793,
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"openwebmath_score": 0.5791048407554626,
"tags": null,
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newtonian-mechanics, forces, newtonian-gravity, work, potential-energy
It's not the size of Earth's mass that matters, it's the radius of the Earth. The difference between 6371 km and (say) 10 m more is tiny, hence the gravitational acceleration is, to a good approximation, constant at reasonable heights close to the surface.
Atmospheric pressure can be discounted as trivial.
Note: I had also assumed that at n distance gravity exerts a continually weakening effect which allows travelling bodies to slingshot into the gravitational orbit of a body and then back out again as gravity is weaker.
I would be careful if you are thinking of this reason to explain probes using the gravity assist of planets, for example the Cassini spacecraft various excursions between planets to pick up speed.
If you search this site, you will find Gravity Assist answers that will explain how this slingshot effect works, and it is not as straightforward as you may think. | {
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haskell, reinventing-the-wheel
Title: Implementing `split` I implemented the split function in Haskell:
split :: (Eq a) => a -> [a] -> [[a]]
split _ [] = []
split x ys = f : split x rest
where (f, rest) = break (== x) (dropWhile (== x) ys)
Note that I'm calling dropWhile (== x) since break's second-tuple value will include the "broken on" value.
example:
*Main> break (== 'a') "dogacactus"
("dog","acactus") | {
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number-formats
What is going on here in Plain English?
If $x$ is almost any nonzero 2-adic integer, we can write its bits in
the form $$x = (\alpha01^a10^b)_2 $$
in other words, $x$ consists of some arbitrary (but infinite) binary
string of $\alpha$, followed by a $0$, which is followed by $a+1$
ones, and followed by $b$ zeros, for some $a \geq 0$ and $b \geq 0$.
(The exceptions occur when $x = -2^b$; then $a = \infty $)
Consequently
$$ \bar{x} = (\bar\alpha10^a01^b)_2 $$
$$ x-1 = (\alpha01^a01^b)_2 $$
$$ -x = (\bar\alpha10^a10^b)_2 $$
and we can see that $\bar{x} +1 = -x = \overline{x-1}$, ...
With two operations we can therefore compute relatives of $x$ in
several useful ways: | {
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fluid-dynamics, pressure, fluid-statics, thought-experiment
When pressure of a liquid water is increased, say, by moving a piston in a blocked syringe filled with water, water temperature increase is very small and is usually neglected.
Now to your question - gravity isn't necessary for pressure either. What is necessary to increase pressure is some other body that will squeeze the gas or liquid into smaller volume. On Earth, this body is the Earth with its gravity, but the same pressure is achieved in a closed vessel, such as the International Space Station, simply by making it robust enough to withstand the pressure and pushing in enough amount of gas. There is no effective gravity there, but there is pressure close to 100kPa, due to walls not allowing the gas to escape. | {
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} |
But even in these days were you can just ask Siri for the answer, it's still a handy skill. It's easier to compare sizes of numbers if the denominators are rational. Some integrands are easier to integrate if the radicals are moved to the numerator. And probably some other things I can't think of.
So asking students in pre-calc to put their answers in this standard form is preparing them for later stuff.
We don't need it. In fact your answer is correct. However, it is standard practice to rationalize those type of fractions. This makes it easier to compare result; it's like having some sort of "standard representation" of a number instead of several, much in the same way as when we write $1/3$ and not $27/81$ | {
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thermodynamics, phase-transition
Is total pressure and not partial pressure the relevant quantity here | {
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image-processing, image-compression, soft-question
Is this true? How does one explain this counterintuitive phenomenon? It depends how you define the term "information" or "entropy".
The conventional definition of entropy of an image is to think the image as a two-dimensional matrix of pixels and
$$H = - \sum_k p_k \log_2(p_k),$$
where $p_k$ is the probability, which is calculated from histogram, associated with gray level $k$.
This kind of entropy is correct if we ignore the correlation between pixels. For example the two images have the same entropy by this definition.
It is not true if the correlation between pixels is considered. For example if the color first pixel in top-left has probability $p_k$, the next pixel surely has the same color and its color does not have the same probability $p_k$. | {
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The second derivative has a constant value of $1/90$, which is smaller than the maximum value of the second derivative of the cosine functions ($1/60$) and the cubic polynomial ($\approx 1/72$). The function spanning the full width would be $$y(x) = \left\{ \begin{array}[ll] \\ -\frac{x(x+120)}{180} & x \lt 0 \\ \frac{x(x-120)}{180} & x \geq 0 \\ \end{array} \right.$$ | {
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homework-and-exercises, newtonian-mechanics, newtonian-gravity, orbital-motion, projectile
Title: In what direction should you throw a 1 kg uniform sphere in order to put it into lower Earth orbit? If you are standing on Earth's surface, in what direction (and at what speed) should you throw a 1 kg uniform sphere of radius 0.1 meters in order to put it into lower Earth orbit? Assume that there is air, but it is not moving relative to the earth. If we ignore air resistance for a moment, then all orbits in an inverse square force like gravity are closed. this means that if you throw something hard enough it will complete one orbit then return to its starting point i.e. your hand.
So if you throw the object downwards it obviously hits the Earth, and if you throw it straight upwards it goes up then down and hits the Earth. For all the angles in between the object will go into orbit, though it will be an exceedingly low orbit since once an orbit it will pass through the point where you released it. | {
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np-hard, linear-programming, weighted-graphs, integer-programming
Can we choose $\alpha < 1/2$? Yes, but the approximation ratio is $1/\alpha$ (because if $x^*_u = \alpha$, then $x_u = 1$ and the associated cost goes from $w_u x^*_u$ to $w_u x_u$, hence is multiplied by $1 / \alpha$). So rounding from $1/3$ is worse that rounding from $1/2$, but is nevertheless a valid approximation algorithm. | {
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performance, validation, r
"13:25:00", "16:35:00", "17:15:00", "18:00:00", "19:00:00", "20:00:00",
"20:40:00", "21:00:00", "22:50:00", "23:00:00", "23:50:00", "00:00:00",
"01:45:00", "06:45:00", "08:00:00", "09:00:00", "12:00:00", "13:00:00",
"17:00:00", "18:50:00", "23:15:00", "23:45:00", "00:00:00", "00:15:00", | {
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particle-physics, statistical-mechanics, probability, statistics, identical-particles
$$p(n_1,n_2,...)=\prod\limits_k\frac{e^{-\beta n_k(E_k-\mu)}}{\sum\limits_{n_k'}e^{-\beta n_k'(E_k-\mu)}},$$
where $\beta$ and $\mu$ are parameters corresponding to the inverse temperature, $(k_BT)^{-1}$ and chemical potential. If we take the marginal distribution for a single occupation number, say, $n_j$, by summing over all other possible values for all the other occupation numbers, we get the probability distribution for the occupation number in question:
$$p_j(n)=\frac{e^{-\beta n(E_j-\mu)}}{\sum\limits_{n'}e^{-\beta n'(E_j-\mu)}}.$$
The step further taken by Bose-Einstein and Fermi-Dirac statistics is now computing the average, or expected occupation number of the quantum state $j$:
$$f_j=\langle n_j\rangle=\sum\limits_nnp_j(n).$$
A nice computational trick is then writing $f_j$ as follows:
$$f_j=\frac{\sum\limits_nne^{-\beta n(E_j-\mu)}}{\sum\limits_{n'}e^{-\beta n'(E_j-\mu)}}$$ | {
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ros, gazebo, ros2, camera
<inertial>
<mass value="1e-5" />
<origin xyz="0 0 0" rpy="0 0 0"/>
<inertia ixx="1e-6" ixy="0" ixz="0" iyy="1e-6" iyz="0" izz="1e-6" />
</inertial>
</link>
<joint name="camera_joint" type="fixed">
<axis xyz="0 1 0" />
<origin xyz="0 0 0" rpy="0 0 0"/>
<parent link="link_4"/>
<child link="camera_link"/>
</joint>
<gazebo reference="base_link">
<material>Gazebo/Black</material>
</gazebo>
<gazebo reference="link_1">
<material>Gazebo/Orange</material>
</gazebo>
<gazebo reference="link_3">
<material>Gazebo/Orange</material>
</gazebo>
<gazebo reference="link_2">
<material>Gazebo/Red</material>
</gazebo>
<gazebo reference="link_4">
<material>Gazebo/Red</material>
</gazebo>
<gazebo reference="link_5">
<material>Gazebo/Orange</material>
</gazebo> | {
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So, there are multiple ideas here. | {
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"tags": null,
"url": "https://brilliant.org/discussions/thread/which-payoff-do-you-want-to-go-for-2/"
} |
photons, elementary-particles
It isn't possible for two people to see the same photon. | {
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For other planes you can change the FindRoot criteria, for instance FindRoot[2 ip[[3]][t] + ip[[2]][t] == 0.5, {t, 10}]
-
Thanks for that. I had trouble finding all of the crossings though using FindRoot. I incorporated it into a forward seach style algorithm but I was still missing some points. I also tried to use FindInstance. Thanks for the answer. +1 – fizzics Jun 12 '13 at 9:00
Defining a function P[x_,y_,z_] := a x + b y + c z for suitable constant values a, b, c, the plane is the set of all points P[x, y, z] == 0, i.e. points that satisfy this equation are on the plane. Points for which P[x, y, z] > 0 are on one side of the plane, while those giving P[x, y, z] < 0 are on the other side.
So, the points you want are those on your curve with P[x, y, z] == 0, or an interpolation between any successive points on your curve that give opposite signs for P`.
- | {
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"url": "http://mathematica.stackexchange.com/questions/26818/how-do-i-find-the-intersection-of-a-closed-3d-curve-given-by-numerical-data-with"
} |
electromagnetism, waves, electromagnetic-radiation, boundary-conditions, dielectric
Title: How to mathematically express permittivity as a function of frequency I am a amateur physics student. I am modelling the wave propagation of an EM wave at different frequencies through water placed between two acrylic rectangular materials using COMSOL. But since the frequency varies the permittivity of the substance changes accordingly. Can anyone help me in this regard? Provided you know the actual dielectric constant $\epsilon_r=\epsilon_r\left(\nu\right)$, where $\nu$ is the frequency, i.e. provided you have a CSV file with two columns (or equivalent), you simply create a function (Model->Global Definitions->Functions->Piecewise) using your CSV file. You can then use this function as the input for your water material. It is not difficult, but requires some practice. Maybe there are Youtube videos available.
Which version of COMSOL? | {
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How is the set of functions from ${\{a,b\}}$ to $N$ countable?
Assume a set of functions from $${\{a,b\}}$$ to $$N$$
Where $$N$$ is the set of Natural numbers.
Let us assume that the size of $$N$$ is $$n$$.
i.e $$|N|=n$$
The first element $$a$$ have $$n$$ choices for mapping.
The second element $$b$$ have $$n$$ choices for mapping as well.
So the number of functions = $$n.n$$ = $$n^2$$. which is strictly greater than $$n$$ and hence the size of $$N$$. So "Set of functions from $${\{a,b\}}$$ to $$N$$", should not be countable. But it is. I am just a beginner in discrete maths, so this might be a stupid question for some. But please explain.
• Things that are true for finite cardinalities need not be true for infinite cardinalities. Dec 31 '19 at 23:00
You are confusing countable and finite. A finite set is always countable, however a countable set can be infinite. | {
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"url": "https://cs.stackexchange.com/questions/119063/how-is-the-set-of-functions-from-a-b-to-n-countable"
} |
c#, event-handling, delegates, e-commerce
Title: Shopping cart using events and delegates I am trying to learn events and delegates in C#. To do that I am trying to create a hypothetical console project where when some user submits the orders in his/her shopping cart, I need the Billing department and mailing department to handle that event. Can someone please critique this code for doing the same?
using System;
using System.Collections.Generic;
namespace LearnEvents
{
class Program
{
static void Main(string[] args)
{
var shoppingCart = new ShoppingCart(10);//shopping cart for user number 10
var bd = new BillingDepartment(shoppingCart);
var md = new MailingDepartment(shoppingCart);
shoppingCart.Add(75458);
shoppingCart.Add(54693);
shoppingCart.Add(52145);
shoppingCart.Submit();
}
} | {
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python, performance, beginner, pygame
pygame.draw.rect(self.Gamewindow, object_enemy.color(randint(0, len(COLORS)-1)), object_enemy.rect)
for object_tower in self.tower:
self.Gamewindow.blit(object_tower.image, object_tower.rect)
self.Gamewindow.blit(light_image_map1, background_rectangle)
button_text("Start next wave", 0, 600, WINDOWWIDTH, 100, PURPLE, LPURPLE, MainWindow.wave)
pygame.display.update() | {
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python, web-scraping, beautifulsoup, selenium
Build up a list of urls you want to download (perhaps with python)
Use wget -nc -i urls.txt to download them
Repeat as necessary
For you, that would involve making a list of urls containing the images. Then do wget -nc -i pages.txt. That will download all of the pages to the current directory. Then you can make a Python script which uses beautiful soup (and the line I mentioned above) to extract the image urls: python3 extract_image_urls.py > image_urls.txt. Then to download them do wget -nc -i image_urls.txt. If your python script fails at any point, you don't lose all of the downloads you've already done. You can wrap all of this in a convenient bash script. | {
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electromagnetism, electromagnetic-induction
If so, then there will be magnetic flux through the rod, but as it moves through the field, the magnetic flux will remain the same, so there will be no induced emf in the rod.
Would it be correct to say that there are 2 sources of induced emf in the rod: one from the separation of positive and negative charges and another one from induced emf via Faraday's law (which is doing nothing).
Does that mean that when a rod first enters a magnetic field, the magnetic flux through the rod will increase and there will be an emf induced? Would it mean there will be 2 contributing emfs in the rod, one from the separation of charges and one from the increase in flux linkage by Faraday's Law?
I can't find answers for this online. For a bit more about my knowledge level on this subject, I do not know anything about Maxwell's equations and what they might imply. The emf in a moving wire arises from the magnetic Lorentz forces acting on the free electrons, as they are carried along by the wire... | {
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php, mvc, controller, codeigniter
Please help me with useful feedback and suggestions. Foreword
I haven't used CodeIgniter in the past so I am not as well-versed with the idiomatic ways it is used but I have used similar frameworks like Laravel.
I did look at the code in the github repository for references (e.g. the routes) but am mostly planning to review the code embedded directly in the post.
General Feedback
I see a fair amount of repeated code. It is wise to abstract out such repeated blocks into methods (make them private if you wish) and call those methods when appropriate. That way if a change needs to happen to each place, it can be done in one spot instead of each occurrence.
In this presentation about cleaning up code Rafael Dohms talks about limiting the indentation level to one per method and avoiding the else keyword. (see the slides here). | {
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multipath
Title: how to simulate multipath fading? I want to simulate a multipath fading channel, different amplitude and delay is given. I want to use delay in padding style. I read that the different values for delay like [0 .6 3.1 ...] represent the delay between the first and last signal arrival? Giving the number of paths, How to simulate it?
regards @MohammedFatehy If you put up -exactly- what you currently know and have, we can help you more.
Generally speaking, let us say you have a signal x[n]. And lets say your sampling rate is 1 Hz. So you take one sample every second.
Now you want to construct a channel for multipath. Right off the bat, your multipath channel is going to be an FIR filter btw. Let us say someone tells you, "your first echo is going to be 5 seconds away, and attenuates the amplitude by 50%. The second echo is going to be 8 seconds away, and attenuates the amplitude by 70%". | {
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visible-light, infrared-radiation, efficient-energy-use
Title: Is it possible to improve the efficacy of light bulbs with a semipermeable mirror? (The greenhouse bulb) Let us imagine that there exists a material that reflects infrared radiation, but is transparent for visible light. Could we take an incandescent bulb and add this material to the inner surface of the glass hull? Then most of the infrared radiation isn't lost, but reflected onto the wire again. So we would need much less energy to heat up the wire to a sufficient temperature. The result would be an efficient light bulb with a broad, gapless spectrum in the visible range.
Is this possible like that? Have I done a fundamental mistake? Or do the required materials not exist? Many light bulbs already do this. See for example this article. I was in the lighting technology business at one point. At that time it was done in some tungsten-halogen incandescents. I don't know current state of things. | {
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"tags": "visible-light, infrared-radiation, efficient-energy-use",
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python, python-3.x, pygame, snake-game
while True:
for event in pygame.event.get():
if event.type == pygame.QUIT:
pygame.quit()
sys.exit()
if event.type == self.keys["GO"] and event.key == self.keys["RIGHT"]:
self.direction = (1, 0)
if event.type == self.keys["GO"] and event.key == self.keys["LEFT"]:
self.direction = (-1, 0)
if event.type == self.keys["GO"] and event.key == self.keys["UP"]:
self.direction = (0, -1)
if event.type == self.keys["GO"] and event.key == self.keys["DOWN"]:
self.direction = (0, 1)
self.move_snake()
self.fps.tick(12)
def move_snake(self):
self.xpos += self.direction[0] * 16
self.ypos += self.direction[1] * 16
self.snake_tail.append([self.xpos, self.ypos])
segment = self.snake_tail.pop(0) | {
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"tags": "python, python-3.x, pygame, snake-game",
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quantum-field-theory, renormalization
Title: Conversion between $\beta (e)$ and $\beta (\alpha)$ Under the entry Beta function (physics) in Wikipedia, the one-loop beta function in electrodynamics (QED) is given by
\begin{equation}
\beta(e) = \frac{e^{3}}{12\pi^{2}} ,\tag{1}
\end{equation}
or, equivalently,
\begin{equation}
\beta(\alpha) = \frac{2\alpha ^{2}}{3\pi} ,\tag{2}
\end{equation}
where
\begin{equation}
\alpha = \frac{e^2}{4\pi} .\tag{3}
\end{equation}
I am puzzled by the conversion between (1) and (2). I plug (3) into (2) and get
\begin{equation}
\beta (e) = \frac{e^4}{24\pi ^{3}}
\end{equation}
But this is not right. How should I make the conversion? The "argument" of $\beta$ here is actually referring to the variable which gets differentiated, i.e.
$$\begin{align}
\beta(e) &= \frac{\partial e}{\partial \ln\mu} &
\beta(\alpha) &= \frac{\partial \alpha}{\partial \ln\mu}
\end{align}$$ | {
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} |
general-relativity, differential-geometry, tensor-calculus, curvature, differentiation
Title: How to derive the formula for the second covariant derivative? If the first covariant derivative is derived by taking the partial derivative of a vector and applying the product rule to the vector components and the vector bases, couldn't the same thing be done to take the second covariant derivative (i.e. use the product rule to the components and bases of the covariant derivative already taken)? Why is it that the formula for the covariant derivative of a rank two tensor must instead be used instead of just taking the second partial derivative of the vector using the product rule as mentioned above? If $\nabla_X= X^\mu D_\mu$ is the covariant derivative on any tensor, then
the usual definition of the "second covariant derivative" is
$$
\nabla^2_{U,V} = \nabla_U \nabla_V -\nabla_{\nabla_U V}.
$$
The second term in gets rid of the derivative of $V$
so that
$$
\nabla^2_{U,V} = U^\mu V^\nu D_\mu D_\nu
$$
with an extra connection term tacitly understood in $D_\mu$: | {
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The antiderivative of the Weierstrass function is fairly smooth, i.e. not too many sharp changes in slope. This just means that the Weierstrass function doesn't rapidly change values (except in a few places).
-
What did you use to plot these? – Mike Miller Jun 11 '14 at 1:46
MATLAB. It took me a bit of playing around to figure out what values of $a$ and $b$ were used to generate the picture on Wikipedia. – JimmyK4542 Jun 11 '14 at 1:52
Neat. What specifically did you run to get your second picture? I might try and run a longer computation to get an even better picture. – Mike Miller Jun 11 '14 at 1:53
I computed the sum of the first 25 terms in the series for values of x ranging from -2 to 2 in increments of 10^-5. It ran in about 6 seconds (MATLAB is slower than other languages). With 25 terms, we get a maximum error of ~6.0x10^-8 for the function and ~1.3x10^-20 for the antiderivative. – JimmyK4542 Jun 11 '14 at 2:07 | {
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java, multithreading, unit-testing, queue, logging
private StringBuilder queue(String msg, String cls, String func) {
Date date = new Date(System.currentTimeMillis());
// $time . ": " . $func . ": " . $msg ."\n"
StringBuilder msgBuilder = new StringBuilder();
msgBuilder.append(new SimpleDateFormat("H:mm:ss").format(date));
msgBuilder.append(": ");
msgBuilder.append(cls);
msgBuilder.append("->");
msgBuilder.append(func);
msgBuilder.append("()");
msgBuilder.append(" :: ");
msgBuilder.append(msg);
try {
_queue.put(msgBuilder);
}
catch (InterruptedException e) {
flush(new StringBuilder(e.toString()));
flush(msgBuilder);
}
return msgBuilder;
}
}
So I created a unit test to check if overloading the log writing with multiple writes at once will ensure all events get written. I toggled between using two blockingqueue approaches. | {
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organic-chemistry, nomenclature, heterocyclic-compounds
The exact structure is specified with indicated hydrogen. There are four 1,4-diazepine structures, 1H-1,4-diazepine, 2H-1,4-diazepine, 5H-1,4-diazepine, and 6H-1,4-diazepine (not considering their stability/existence in tautomeric pair/multiple):
In the world of abstract organic chemistry nomenclature, 1,4-diazepine without indicated hydrogen can be represented as following structure (dotted bonds for unknown bond order, any arrangement of noncumulative dbl. bonds assumed; no explicit hydrogens): | {
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sage: gcd( x^49 - x, f )
1
sage: gcd( x^(7^4) - x, f )
x^4 + x^3 + x^2 + x + 1
For this, one can also compute easily $(x^{49}-x,f)$ as a human by noting that $f$ divides $x^5-1$, so $(x^{49}-x,f)=(x^{49}-x^4+x^4-x,f)=(x^4-x,f)=(x^3-1,f)=(x^2+x+1,f)=(x^2+x+1,x+1)=(1,x+1)=1$.
HINT.-If $x^4+x^3+x^2+x+1$ were reducible then we have either a linear factor with a cubic one or two quadratic factors.
We have $$x^4+x^3+x^2+x+1=-\dfrac 14(-2x^2+(\sqrt5-1)x-2)(2x^2+(\sqrt5+1)x+2)$$ Since $\mathbb F_7^2=\{1,2,4,0\}$ we see that $5$ is not a square modulo $7$. It follows $x^4+x^3+x^2+x+1$ is not a factor of two quadratics modulo $7$.
Besides that a linear factor is not possible is checked easily. | {
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analytical-chemistry, ir-spectroscopy
Figure 2, from the above-referenced article. FA is fulvic acid and HA is humic acid. | {
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Then, as @Leonid indicates, we can, indeed, use the inverse function theorem [1]. In particular, assume that $$\frac{\left\|\mathbf{v}\right\|^2}{c^2} \neq 1$$. Then, adapting from [1], I write as follows. I have a function $$\tau$$ of a single variable $$t$$. The inverse function theorem states that since $$\tau$$ is a continuously differentiable function with nonzero derivative at the point $$t_a$$; then $$\tau$$ is injective in a neighborhood of $$t_a$$, the inverse is continuously differentiable near $$\tau_b=\tau(t_a)$$, and the derivative of the inverse function at $$\tau_b$$ is the reciprocal of the derivative of $$\tau$$ at $$t_a$$. In other words, $$\bigl(\tau^{-1}\bigr)'(\tau_b) = \frac{1}{\tau'(t_a)} = \frac{1}{\frac{1}{\gamma }} = \gamma.$$ | {
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optics, experimental-physics, geometric-optics
P.S. I want to know for a cube beam splitter, but for future reference it might also be good to include plate- and pellice beam splitters. Short answer:
The transmitted beam has the same direction as the incident beam. It is only shifted by
$$d = a \left( \sin \alpha - \frac{\cos \alpha}{\sqrt{\frac{\left( \frac{n_\text{glass}}{n_\text{air}} \right)^2}{\sin^2 \alpha} - 1}} \right),$$
where $\alpha$ is the tilt angle, $a$ is the edge length of the beamsplitter cube and $n_\text{glass}$ and $n_\text{air}$ are the refractive indices of the beamsplitter material and the surrounding medium, respectively.
The reflected beam is rotated by $2\alpha$ when the beamsplitter is rotated by $\alpha$. This is the same as when a simple mirror is rotated. | {
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ros, hardware, ros-melodic
ON-Robot RG2 and RG6
SAKE Robotics Gripper
Adaptive Fin-Ray-like gripper from Aliexpress (search "adaptive gripper")
In the end, I decided for the SAKE Robotics gripper, since it seems to fit my application very well and the pricing is lower than the ON-Robot and Robotiq solutions. Moreover, the SAKE gripper comes with ROS drivers and simulation models.
I couldn't find suitable electric long-stroke parallel grippers, so I discarded the fin-ray finger option.
Originally posted by machinekoder with karma: 69 on 2019-12-16
This answer was ACCEPTED on the original site
Post score: 0 | {
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of the Fibonacci sequence. As we can see above, each subsequent number is the sum of the previous two numbers. Yes, there is an exact formula for the n-th … 0 1 Let’s create a new Function named fibonacci_with_recursion() which is going to find the Fibonacci Series till the n-th term by calling it recursively. The number in the nth month is the nth Fibonacci number. n I went offline for two days because I had to go on a trip and stuff, but then I found 17 Notifications (in general), 62 upvotes and a few comments on this answer. is valid for n > 2.[3][4]. [clarification needed] This can be verified using Binet's formula. The male's mother received one X chromosome from her mother (the son's maternal grandmother), and one from her father (the son's maternal grandfather), so two grandparents contributed to the male descendant's X chromosome ( n The next number can be found by adding up the two numbers before it, and the first two numbers are always 1. [17][18] Fibonacci considers the | {
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quantum-mechanics, quantum-interpretations, decoherence
Consider the position of a pointer. We don't interpret non-narrowly pointed states of the pointer as physical, basically by the very definition of what we mean by "a pointer" (after all, we take for granted that some systems can only occupy narrow states, and these are called pointer states in common terminology). In quantum mechanics, the non-narrow states of the pointer are perfectly valid. Then how does the pointer come in practice to inhabit the narrow states? | {
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ros, rviz, ros-kinetic, geometry-msgs, joint-state-publisher
Title: Publish and subscribe Using Joint_state_publisher for real robot
hello guys,
I'd like to ask you some question about using joint_state_publisher for real robot. I'm using arm robot and I want to control it using joint_state_publisher. but I have a question :
how to visualize and control real robot (especially manipulator) movement by RViz (not moveit)?
I still confuse about JointState and can I using it to get Pose (with geometry_msgs)?
thank you! | {
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machine-learning, neural-network, deep-learning, tensorflow, pytorch
Title: How to train a neural network on multiple objectives? I have a multi-class neural network classifier that has K classes(products). For every row, only one of the classes will be 1 at a time. Now, this approach works fine if I have only 1 objective to optimize i.e Which of these N products was "clicked" by the user.
But how will I solve this problem if I need to optimize on a 2nd objective i.e Which of these N products was "purchased" by the user?
A purchase event is always preceded by a click event. I can obviously solve this problem by training two separate models - 1 for click and the other for purchase. But purchase data is very low as compared to the click data. And we ran the purchase model on production. It did not perform well.
So how do I take both the click and purchase data and frame my problem as "Which of these N products will be clicked and possibly purchased by the user"? and train a single model. | {
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symmetry, gauge-theory, symmetry-breaking
That Lindblad form then describes a nonunitary dynamics and you can look there for things like dissipation, and you can try to convert it to a stochastic equation and do numerical simulations. But in the spontaneous-symmetry-breaking side, that can create a flow from the center of the Mexican hat out towards the ground states. | {
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javascript, performance
}
});
}
return result;
},
// ---------------------------------------------------------------------
// :: formatting aware substring function
// ---------------------------------------------------------------------
substring: function substring(string, start_index, end_index) {
var chars = $.terminal.split_characters(string);
if (!chars.slice(start_index, end_index).length) {
return '';
}
if (!$.terminal.have_formatting(string)) {
return chars.slice(start_index, end_index).join('');
}
var start = 0;
var end;
var start_formatting = '';
var end_formatting = '';
var prev_index;
var offset = 1;
$.terminal.iterate_formatting(string, function callback(data) {
if (start_index && data.count === start_index + 1) {
start = data.index;
if (data.formatting) { | {
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rosmake
[rosmake-0] Starting >>> diagnostic_updater [ make ]
[rosmake-2] Starting >>> python_orocos_kdl [ make ]
[rosmake-2] Finished <<< python_orocos_kdl ROS_NOBUILD in package python_orocos_kdl
[rosmake-0] Finished <<< diagnostic_updater ROS_NOBUILD in package diagnostic_updater
[rosmake-2] Starting >>> kdl [ make ]
[rosmake-3] Starting >>> dynamic_reconfigure [ make ]
[rosmake-3] Finished <<< dynamic_reconfigure ROS_NOBUILD in package dynamic_reconfigure
[rosmake-0] Starting >>> self_test [ make ]
[rosmake-2] Finished <<< kdl ROS_NOBUILD in package kdl
No Makefile in package kdl | {
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algorithms, graphs, shortest-path
Since -2 is "shorter" than -1, after we finish k = 1, the weight for i -> k = 1 -> j is -2 for most i and j (exceptions would be i = k and j = k).
After we finish k = 2, the weight for i -> k = 2 -> j is -4 for most i and j. This is because i -> 1 -> 2 -> 1 -> j is the shortest, giving us -4.
And so on and so on for the exponential growth.
Floyd-Warshall algorithm does not guarantee that we will find a simple shortest path, that is, a path containing only one instance of each vertex. | {
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safety, esters
At home, you typically do not have that possibility. However, the basic advice remains the same: store in the original container (if possible) and in a well-ventilated area away from spark sources. The original bottle should, in theory, be airtight enough — remember that the ethyl acetate must have somehow found its way to you in that bottle without having lost too much content.
I would strongly advise against storing in a closed drawer. As you noticed, a few months were enough for enough solvent to evaporate but stay in the vicinity for you to smell it. The amount of solvent you lose per unit of time is typically very small and if it can diffuse away it does not do much harm. But the closed drawer prevented it from efficiently diffusing away and allowed it to concentrate. | {
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vba, excel
End If
End If
Next
Next
End Select
End If
End If
GetArrIndxOfStr = indx 'string containing an index for each dimension in array
End Function | {
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string-theory, conformal-field-theory, degrees-of-freedom, brst, ghosts
$$c = \frac{k\ \mathrm{dim}(G)}{k+\kappa(G)}$$
Where $k$ is the level and $\kappa$ is the dual Coxeter number. Please see the following
article by Juoko Mickelsson.
One of the best ways to understand this fact (and in addition the ghost sector central extension) is to follow the Bowick-Rajeev approach described in a series of papers, please see for example the following scanned preprint. I'll try to explain their apprach in a few words.
Bowick and Rajeev use the geometric quantization approach. They show that the Virasoro central charges are curvatures of line bundles over $Diff(S^1)/S^1$ called the vacuum bundles.
Bowick and Rajeev quantize the space of loops living on the matter field manifold.
This is an infinite dimensional Kaehler manifold. One way to think about it | {
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operators, gauge-theory, constrained-dynamics, brst, ghosts
Title: Square of BRST operator The BRST operator $\Omega$ can be expanded in powers of the ghost fields $c^{\alpha}$ and their conjugates $b_{\alpha}$ (which satisfy $\{c^\alpha,b_\beta\}=\delta^{\alpha}_{\beta}$):
$$
\Omega=c^{\alpha_1}M_{\alpha_1}+c^{\alpha_1}c^{\alpha_2}b_{\beta_1}M^{\beta_1}_{\alpha_1\alpha_2}+c^{\alpha_1}c^{\alpha_2}c^{\alpha_3}b_{\beta_1}b_{\beta_2}M^{\beta_1\beta_2}_{\alpha_1\alpha_2\alpha_3}+O(c^4)
$$
Notice that this is normal-ordered because the $c^\alpha$ are considered creation operators and the $b_\alpha$ are annihilation operators. | {
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opencv, ros-melodic
[ 16%] Built target compressed_depth_image_transport_gencfg
[ 33%] Building CXX object CMakeFiles/compressed_depth_image_transport.dir/src/codec.cpp.o
/home/tyler/workspace/ws_ros_melodic/src/image_transport_plugins/compressed_depth_image_transport/src/codec.cpp: In function ‘sensor_msgs::Image_<std::allocator<void> >::Ptr compressed_depth_image_transport::decodeCompressedDepthImage(const CompressedImage&)’:
/home/tyler/workspace/ws_ros_melodic/src/image_transport_plugins/compressed_depth_image_transport/src/codec.cpp:138:49: error: ‘CV_LOAD_IMAGE_UNCHANGED’ was not declared in this scope
cv_ptr->image = cv::imdecode(imageData, CV_LOAD_IMAGE_UNCHANGED);
^~~~~~~~~~~~~~~~~~~~~~~
CMakeFiles/compressed_depth_image_transport.dir/build.make:134: recipe for target 'CMakeFiles/compressed_depth_image_transport.dir/src/codec.cpp.o' failed
make[2]: *** [CMakeFiles/compressed_depth_image_transport.dir/src/codec.cpp.o] Error 1 | {
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c#, linq, error-handling
And this isn't necessarily a bad thing. It depends on what the client code is expecting.
We don't know what class this method is a member of. The problem is that the naming of the method doesn't convey any information about what's going on, and whether the calling code should wrap it with a try/catch block. If the class is clearly an object that accesses a database and only does SELECT operations, then it's probably fine. Otherwise the method's name should say what it's doing - SelectTopCodeForToday() would be a better name regardless of all of the above, be it only because it starts with a verb. | {
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special-relativity, mass, speed-of-light, momentum
The math absolutely is symmetric between acceleration and deceleration (because velocity enters in to the Lorentz factor squared), and we have machines that take advantage of this fact.
Energy recovery linacs work in exactly the manner linacs usually work, only the field timing is maintained 180 degrees out of phase from the acceleration mode. This means that instead of the particle gaining energy at the expense of the field, the field gains energy at the expense of the particle. The forces are the same as in the accelerating case only opposed to the direction of motion, and the particle exhibits the same magnitude of coordinate acceleration (i.e. very little because it is highly relativistic) in the lab frame only slowing rather than speeding up. | {
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"tags": "special-relativity, mass, speed-of-light, momentum",
"url": null
} |
ubuntu, ros-fuerte, ubuntu-precise, openi-tracker, nite
Comment by Mike Gao on 2012-09-03:
And when I run the openni_tracker alone, the program still stucks...
Comment by Mike Gao on 2012-09-03:
It seems that the solution works finally, thanks again!
Comment by bit-pirate on 2012-12-10:
Thanks, works like a charm now! :-)
Comment by niosus on 2012-12-14:
Thanks a lot! Works for me too.
Comment by bit-pirate on 2013-04-15:
I believe the download page has been moved to: http://www.openni.org/openni-sdk/openni-sdk-history-2/
Comment by thorin on 2013-10-29:
Hey Mike Gao, my node also got stuck. How did you solve this?
Comment by Mike Gao on 2013-12-10:
Hi, after having installed ros hydro, I do not have such problem anymore.
Since openni.org site has changed recently. You should do the following to do as @pgorczak suggested.
You need to install the NiTE v1.5.2.21 middleware from:
www.openni.ru/openni-sdk/openni-sdk-history-2
Assuming you extracted the file to your Downloads directory, do the following: | {
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} |
image-processing, matlab, fft, fourier-transform, dft
According to source code, the plot of extracted waves is the real part of the Inverse Fourier Transform of the sum of nWaves spectral components $F(s,t)$ with maximum amplitude:
\begin{equation}
f(x,y) = \frac{1}{NM}\sum\limits_{s,t\in U}Re\big(F(s,t)e^{2\pi i(sx/N + ty/M)}\big)
\end{equation}
where $f(x,y)$ is the value of the $(x,y)$ pixel of the extracted waves image in the spatial domain, $F(s,t)$ is the value of the $(s,t)$ component in the frequency domain, $U$ is first nWaves frequency components with $\max|F(s,t)|$.
So these waves aren't cosine nor sine. They are non trivial linear combination of sine and cosine waves.
What are basis functions (images) and Whether the plot of Extracted waves are called as basis functions in mathematics?
It's hard to tell without knowing the procedure, that have been used to create those images. But if the procedure is the same as in the video presentation, then it isn't technically correct to call those images Basis Functions. | {
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java, performance, edit-distance
It also does not do well when trying to match strings that have been severely truncated (their description is 1.75x bigger than allowed text in craigslist description) because their edit distance is huge.
About the code
After the text is parsed I have a linked list of strings which are from craigslist, I then create a dummy item for each and have a list of possible items to set to active. So for each possible clItem I go through every item in the inventory until I find a match, then break. (I have multiple of the same inventory items, I only want to set one to true if one of them is posted).
For each comparison between a clItem and a Item in my inventory I call sameItemDesc() which uses the Levenshtein distance to determine if two strings are the same. | {
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continuous-signals, linear-systems, periodic, complex, system-identification
X(t) is the combination of two functions. one is the natural logarithm base, $e$, and the other is 10.
if there is only an exponential function given then we easily calculate the period of the given signal.
but the problem is another function given as $ 10^{j(7t+\pi/5)} $
How is the periodicity calculated if $e$, the natural logarithm base, is not in the base?
edit
yes, it was asked in competitive exams, not as homework.
if $$ 7 e^{\jmath(5t + \pi/2)} $$
then perodicity we calculate as $$2\pi/w$$
so perodicity of exponetial part is $$2\pi/5 $$
i have confusion in this part $ 10^{j7t+\pi/5} $ is perodicity we calculate like same as above $$2\pi/w = 2\pi/7$$
is this correct? A signal $e^{j(\omega t + \varphi)}$ has an angular frequency $\omega$ and period $T=2\pi/\omega$.
The signal $x_1(t) = 7e^{j(5t + \pi/2)}$ thus has period $$T_1 = \frac{2\pi}{5}$$ | {
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computer-architecture
Instruction compression of this kind is good but it comes at a couple of costs. The most important cost is that the instructions are variable length and hard to decode. The 8080 took several cycles to decode each instruction. By the 1980s the cost of memory had come down considerably, and people started to realize that by making instructions easier to decode it would be easier to design high-performance pipelined processors. RISC instructions are designed to be easy to decode (and to not have more than one memory operation so that they can be pipelined). | {
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logic, quantum-computing
Title: Intuition behind the Hadamard gate I'm trying to teach myself about quantum computing, and I have a decent-ish understanding of linear algebra.
I got through the NOT gate, which wasn't too bad, but then I got to the Hadamard gate. And I got stuck. Mainly because while I "understand" the manipulations, I don't understand what they really do or why you'd want to do them, if that makes sense. | {
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# Is the Fibonacci sequence exponential?
I could not find any information on this online so I thought I'd make a question about this.
If we take the Fibonacci sequence $$F_n = F_{n-1} + F_{n-2}$$, is this growing exponentially? Or perhaps if we consider it as a function $$F(x) = F(x-1) + F(x-2)$$, is $$F(x)$$ an exponential function?
I know Fibonacci grows rather quick, but is there a proof that shows whether it is exponential or not?
• Look at Binet's formula en.wikipedia.org/wiki/… Nov 1, 2018 at 21:39
• Yes, of course, it is extremely close to $C \varphi^n \; , \;$ where $\varphi = \frac{1 + \sqrt 5}{2}$ and $C$ is a constant Nov 1, 2018 at 21:39
• @J.G. yah, I lost my focus... Nov 1, 2018 at 21:45 | {
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ros, ros-groovy, dependencies
Depends: ros-groovy-actionlib (= 1.9.11-0quantal-20121230-1206-+0000) but it is not going to be installed
Depends: ros-groovy-pluginlib (= 1.9.17-0quantal-20121230-1110-+0000) but it is not going to be installed
Depends: ros-groovy-image-pipeline (= 1.9.11-0quantal-20121230-2354-+0000) but it is not going to be installed
Depends: ros-groovy-bfl (= 0.1.0-s1356865809~quantal) but it is not going to be installed
Depends: ros-groovy-stage (= 1.6.7-s1356894745~quantal) but it is not going to be installed
Depends: ros-groovy-rqt-robot-plugins (= 0.2.7-0quantal-20121231-2000-+0000) but it is not going to be installed
Depends: ros-groovy-image-common (= 1.9.22-0quantal-20121230-1342-+0000) but it is not going to be installed | {
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html, css
}
#logo {
float: left;
margin-top: 50px;
margin-left: 100px;
}
#topnav {
float: right;
margin-top: 50px;
margin-right: 1250px;
}
#topnav ul {
word-spacing: 10px;
}
#topnav ul li {
list-style-type: none;
display: inline;
}
#columns {
width: 400px;
float: left;
margin-top: 20px;
margin-left: 200px;
}
#col1 {
float: left;
margin-right: 10px;
width: 100px;
border: 1px solid #ffffff;
border-radius: 5px;
height: 80px;
}
#col2 {
float: left;
margin-right: 10px;
width: 100px;
border: 1px solid #ffffff;
border-radius: 5px;
height: 80px;
}
#col3 { | {
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complexity-classes, assignment-problem, resource-allocation
Title: Problem class of assigning N persons to N tasks, zero costs with prefs I am looking for the general problem class / computational complexity / algorithms for the following problem:
N tasks must be accomplished by N persons. 1 task to be done by exactly 1 person and vice versa. There is a binary preferences matrix whose (i,j) entry is 0 if person i can not do task j, and 1 if it can.
There are no costs involved, no weights and the number of tasks equals the number of people.
I was searching for it but all I could find was the Assignment Problem which has costs/weights associated with each assignment.
As a last resort, perhaps I can transform my preferences matrix to a cost matrix if person can not do job then cost is infinite else cost is zero? This problem is known as maximum matching of a bipartite graph.
Basically let vertex $p_i$ (resp., $q_i$) represent the $i$th person (resp., task).
And we connect $p_i$ and $q_j$ with an undirected edge iff person $i$ can do task $j$. | {
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python, python-2.x, stack, interpreter, language-design
def _copy(self):
self.inactive = Stack(self.active)
def _replace(self):
self.active.push(self._simplify(str().replace(str(self.inactive.pop()), str(self.inactive.pop()))))
def _join(self):
for i in self.active:
i = str(i)
x = unicode(''.join(self.active))
self.active.clear()
self.active.push(x)
def _mult(self):
x = self.active.pop()
y = self.active.pop()
if type(x) == str and type(y) == str:
self.active.push(y)
self.active.push(x)
else:
self.active.push(x*y)
# Debug
lang_inst = FOG()
#^!["a"'b'C.ss.jo;]
code = u"""^i_;"""
code = lang_inst._decode(code) | {
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"tags": "python, python-2.x, stack, interpreter, language-design",
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organic-chemistry, reaction-mechanism, erratum, regioselectivity
${}^{1234}$ Sharghi, H.; Eskandari, M.M. Synthesis 2002, 1519.
${}^{1235}$ Ha, J.D.; Kim, S.Y.; Lee, S.J.; Kang, S.K.; Ahn, J.H.; Kim, S.S.; Choi, J.-K. Tetrahedron Lett. 2004, 45, 5969.
${}^{1236}$ Fringuelli, F.; Pizzo, F.; Vaccaro, L. J. Org. Chem. 2001, 66, 4719. Also see Concellón, J.M.; Bardales, E.;
Concellón, C.; García-Granda, S.; Díaz, M.R. J. Org. Chem. 2004, 69, 6923. | {
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python, python-3.x, tree
delete
The delete operation needs the two following steps: 1. find the node having the given key; 2. remove the key. The first step is easy, now but the second one is not. Let's look at your code to understand what happens:
else: # key == cur.key
if cur.left is None:
return cur.right
elif cur.right is None:
return cur.left
else:
def __get_successor(n):
while n is not None and n.left is not None:
n = n.left
return n
successor = __get_successor(cur)
cur.key = successor.key
cur.right = self.__delete(cur.right, successor.key) | {
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"tags": "python, python-3.x, tree",
"url": null
} |
gazebo
[roscpp_internal] [2011-08-13 21:00:31,506] [thread 0x7f8ff3f95700]: [DEBUG] Socket [26] received 0/4 bytes, closing
[roscpp_internal] [2011-08-13 21:00:31,506] [thread 0x7f8ff3f95700]: [DEBUG] TCP socket [26] closed
[roscpp_internal] [2011-08-13 21:00:31,644] [thread 0x7f8ff3f95700]: [DEBUG] Accepted connection on socket [23], new socket [26]
[roscpp_internal] [2011-08-13 21:00:31,644] [thread 0x7f8ff3f95700]: [DEBUG] TCPROS received a connection from [127.0.0.1:40957]
[roscpp_internal] [2011-08-13 21:00:31,644] [thread 0x7f8ff3f95700]: [DEBUG] Connection: Creating ServiceClientLink for service [/gazebo/apply_body_wrench] connected to [callerid=[/rosservice_3864_1313240431528] address=[TCPROS connection to [127.0.0.1:40957 on socket 26]]] | {
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astronomy, history, solar-system, geometry
Form a triangle out the observer, the sun and the moon: $\triangle OSM .$ The only angle the observer can measure directly is of course the angle between the sun and moon, the observer forming the vertex. The sun is in the direction of the horizon, and the 1st-quarter moon is near zenith, hence $\angle SOM \approx 90°.$ | {
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So, it's obvious that the answer can't be $0$ since there's no point of it, it has to be at least one if we have, for example, to pieces left of all the $mn$ pieces that are connected each other. I tried to do a coloring of the infinite board, in a chess pattern, so we have Black pieces (Pieces in a black tile) and White pieces, this make any white piece unable to make dissapear another white one and the same with black ones. At the end, the least we have of each color the better, because if we get to have only two left with different colors and connected, then we'll know the least number of pieces is 1. i tried looking for different rectangles of pieces, and i got 1 and 2 as answers. For example doing the following when $m=3$ and $n=4$ makes the board have 1 piece at the end: (From left to right) | {
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bitwise, coldfusion, cfml
This would most likely require me to set default values as well, but I am okay with that. Yeah, you're not doing yourself any favours by having the elements of the IF conditions in differing orders. It took a bit for me to re-sort everything so I could understand what the heck was going on. I think it distills down to this:
<cfscript>
if (structKeyExists(URL, "after")){
param name="URL.start" default=URL.after type="time";
variables.endDate = today; // I am not sure what scope TODAY is in, but SCOPE IT. TODAY *must* be a valid, unambiguous date string, EG YYYY-MM-DD
}else{
param name="URL.start" default="00:00:00" type="time";
variables.endDate = token; // same as with TODAY: scope it and make sure it's a valid date
}
param name="URL.end" default="23:59:59" type="time";
variables.startDate = token; | {
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"tags": "bitwise, coldfusion, cfml",
"url": null
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required to attempt a solution when no master theorem case applies. The Quantum MacMahon Master Theorem By Stavros Garoufalidis, Thang TQ Le, Doron Zeilberger and X [maybe you!] Warning: The proof is incomplete, read below for a chance to win a prize and be co-author. $$T(n) = \sum_i a_i T(n/b_i) + g(n)$$. f(n)=lgn=O(n2−ϵ) for ϵ=1, since lgn=O(n). For the special case where the Hecke operator is the ordinary supersymmetry and typed all missing steps in LaTeX. There are four main functions associated with heapsort 1. 1: As part of your background section. If f(n) = O(nlogb a− ) for some constant > 0, then T(n) = Θ(nlogb a). Homework that is Chapter 7: The Prime Number Theorem for arithmetic progressions RefTeX wraps itself round four LaTeX macros: \label , \ref , \cite , and \index . Since there is always a power of 2 in the range $[\frac {n} {2}, n]$, recurrence master-theorem 追加された 27 9月 2013 〜で 02:06 著者 WSS , それ マスター定理を使用した次の再帰アルゴリズムの実行時間はどのくらいですか？ The DFS algorithm works as follows: | {
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"lm_q2_score": 0.8807970826714614,
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"openwebmath_score": 0.7071961164474487,
"tags": null,
"url": "http://secure.consumercreditagency.org/ez5a/master-theorem-latex.html"
} |
of multiple linear regression technique on the Boston house pricing dataset dataset using Scikit-learn. Taking binary Aug 11, 2017 · The case of one explanatory variable is called simple linear regression or univariate linear regression. If you prefer, you can read Appendix B of the textbook for technical details. Next, we need to specify a metric we can use to evaluate our linear regression model. Aug 12, 2019 · The model is called Simple Linear Regression because there is only one input variable (x). This MATLAB function returns a vector b of coefficient estimates for a multiple linear regression of the responses in vector y on the predictors in matrix X. There are a variety of linear regression techniques available in the mathematical world. Bretherton Winter 2015 A natural extension is to regress a predictand y on multiple predictor vari-ables x m. That is, we use the adjective "simple" to denote that our model has only predictor, and we use the adjective "multiple" to indicate | {
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"lm_q1q2_score": 0.8032252518056001,
"lm_q2_score": 0.8152324960856175,
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"openwebmath_score": 0.6238495707511902,
"tags": null,
"url": "http://mcsms.ru/carrier-ahu-wgdoq/rmxw---multiple-linear-regression-derivation---3du.html"
} |
python, tic-tac-toe
def to_int(self):
"""Convert 3D coordinates to the cell ID.
>>> grid_size = 4
>>> coordinates = (4,2,3)
>>> PointConversion(grid_size, coordinates).to_int()
39
"""
x, y, z = [int(i) for i in self.i]
if all(i > 0 for i in (x, y, z)):
return (x-1)*pow(self.grid_size, 0) + (y-1)*pow(self.grid_size, 1) + (z-1)*pow(self.grid_size, 2)
return None
class SwapGridData(object):
"""Use the size of the grid to calculate how flip it on the X, Y, or Z axis.
The flips keep the grid intact but change the perspective of the game.
Parameters:
grid_data (list/tuple): 1D list of grid cells, amount must be a cube number.
"""
def __init__(self, grid_data):
self.grid_data = list(grid_data)
self.grid_size = calculate_grid_size(self.grid_data)
def x(self):
"""Flip on the X axis. | {
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Row-Major order
Column-Major order
$${\begin{bmatrix}x & y & z\end{bmatrix} * \begin{bmatrix} a & b & c \\ d & e & f \\ g & h & i \end{bmatrix}}$$ $${ \begin{bmatrix} a & b & c \\ d & e & f \\ g & h & i \end{bmatrix} * \begin{bmatrix}x\\y\\z\end{bmatrix} }$$
$${\begin{array}{l}x' = x * a + y * d + z * g\\y' = x * b + y * e + z * h\\z' = x * c + y * f + z * i\end{array}}$$ $${\begin{array}{l}x' = a * x + b * y + c * z\\y' = d * x + e * y + f * z\\z' = g * x + h * y + i * z\end{array} }$$ | {
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material is taught in the BSc. Numerical Methods for Time-Dependent Differential Equations Dale Durran University of Washington 22 August 2013 Dale Durran (Atmospheric Sci. Cheviakov b) Department of Mathematics and Statistics, University of Saskatchewan, Saskatoon, S7N 5E6 Canada. "Finite volume" refers to the small volume surrounding each node point on a mesh. Temperature profile of T(z,r) with a mesh of z = L z /10 and r =L r /102 In this problem is studied the influence of plywood as insulation in the. Numerical methods can be used to solve many practical prob-lems in heat conduction that involve complex 2D and 3D – geometries and complex boundary conditions. Finite Difference Methods Next, we describe the discretized equations for the respective models using the finite difference methods. Understanding the FDTD Method. The photonic band structures within an irreducible Brillouin zone are investigated for both in plane and out plane propagation. A general optimal method for a 2D | {
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Unless the variable x appears in either (or both) of the limits of integration, the result of the definite integral will not involve x, and so the. Theorem statement. The position y = F(t) is an anti-derivative of the velocity v = f(t). , S= ∂W, then the divergence theorem says that ∬SF⋅dS= ∭WdivFdV, where we orient S so that it has an outward pointing normal vector. The first thing to notice about the fundamental theorem of calculus is that the variable of differentiation appears as the upper limit of integration in the integral: Think about it for a moment. Complex Integration (2A) 3 Young Won Lim 1/30/13 Contour Integrals x = x(t) f (z) defined at points of a smooth curve C The contour integral of f along C a smooth curve C is defined by. Basic Integration Formulas and the Substitution Rule 1The second fundamental theorem of integral calculus Recall fromthe last lecture the second fundamental theorem ofintegral calculus. You will see plenty of examples soon, but first let us see the | {
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For the same reason, the sum of any empty list is zero, and the product is one. This is when a product or sum of an empty list is applied to a number, it leaves it unchanged. Thus if the product $\Pi()$ = 1, then we immediately see why $0! = 0^0 = 1$.
Without this property, one could prove that $2=3$, by the ruse that there are zero zeros in the product on the left (zero is after all, a legitimate count), and thus $2*0^0$, and since $0^0$ as indeterminate, could be 1.5, and thus $2=3$. I think not. | {
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velocity, drag, aerodynamics, aircraft, lift
Title: How find/estimate Parasitic Area (CDA) in order to calculate V(L/D)max? I am trying to calculate the speed which maximizes lift/drag for an aircraft. Using Carson's paper, it looks to me like the only unknown variable is "f", the parasitic area, which Carson describes as "a fictitious area which, when multiplied by the free stream dynamic pressure, equals the viscous drag."
This is where I'm stuck: either I need to find a way to experimentally measure free stream dynamic pressure and viscous drag in order to calculate f, OR I need to find some equation for f based off of measurable qualities of the aircraft. Everything I've found either brushes this calculation off as too difficult, or appears to devolve into a mess of procedures for gross estimations not really related to the actual problem at hand. | {
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quantum-field-theory, special-relativity, momentum, eigenvalue
\begin{equation*}
\mathbf{P} = \sum_i \mathbf{p}_i = 0.
\end{equation*}
The energy of this state is then just
\begin{equation*}
E = \sum_i \sqrt{m^2 + \mathbf{p}_i^2}.
\end{equation*}
Since the $\mathbf{p}_i^2$ can be chosen arbitrarily as long as they still sum to 0, this gives you a continuum. This energy has a lower bound of $E = 2\sqrt{m}$ corresponding to two particles at rest so the contiuum starts there. | {
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python, hash-map
Title: Reverse dictionary where values are lists I'm working on the following problem: I've got a dictionary like this one:
dic={0:[0,1,2],1:[3,4,5]}
And I want to reverse it so it looks like this:
dic2={0:0,1:0,2:0,3:1,4:1,5:1}
I managed to make it, but doing this:
dic2={}
for i in dic:
for j in dic[i]:
dic2[j]=i
I know about list and dict comprehensions and this code reeks of it, but I'm not good at them when there are nested for and dicts. How would you make it more efficiently? There's really not much to say about this code, it is straightforward.
Style
These are only nitpicks. | {
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powershell
$domain_admins = Get-WmiObject -Class Win32_Account |
Where-Object { $_.SID -like '*-512' } |
Select-Object -Expand Caption
Another thing you could do is map names to permissions like this:
$permissions = @{
'Administrators' = 'FullControl'
"$domain\Domain Admins" = 'FullControl'
"$domain\FS-$NAME-RW" = 'Modify'
"$domain\FS-$NAME-R" = 'ReadAndExecute'
}
and use the hashtable as input for the ACE creation:
$permissions.Keys | ForEach-Object {
$acl.AddAccessRule((New-Ace $_ $permissions[$_]))
}
Of course this implies that all ACEs have the same type and flags, otherwise you'd have to use a more elaborate data structure. | {
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neutrinos, nuclear-engineering
Title: Neutrino or antineutrino detection during Chernobyl disaster In the HBO series Chernobyl, they keep dumping sand on top of the reactor and worrying about it melting down into the groundwater. They said they had no way of telling what was happening in the core.
Wouldn't it have been possible to get the state of the core by monitoring neutrinos? The soviets seem to have had reasonable research into neutrinos at that point. | {
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outcome probability distribution they do work – success failure! Trials are independent, the binomial distribution is one of the Social & Sciences. Every trial there are only two possible outcomes – success or failure success p! And its standard deviation, variance and standard deviation for the three binomial distribution on the horizontal axis 10 is! Affect the next outcome results related to binomial distribution representing the number of heads would be where you try score! The binomial distribution is one of the most important discrete distribution and the Poisson distribution seem unrelated possible –! Free throws, make probability per free throw is 80 % symmetrical around its mean and variance formulas the...: n - number of heads one expects to observe—is marked with an ordinary dice little hard prove... The average of anything else which is equal to the submission of product of no related binomial! Of trials rq } { p^2 }$ is 80 % be head or tails binomial.! Sciences, 2001 2.5 | {
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