text stringlengths 1 1.11k | source dict |
|---|---|
quantum-mechanics, condensed-matter, symmetry-breaking, time-reversal-symmetry, ferromagnetism
You suggest that the fact one in principle needs the environment to 'make the choice' that this is not really spontaneous. It is true that in that philosophical sense of the word, the direction of magnetization is not 'spontaneous'. But what can be called spontaneous in the universe? If I perfectly balance an egg, then the direction it will eventually roll when it loses its balance is spontaneous (or not spontaneous) in exactly the same sense. And note that once the egg has rolled down (and stopped), the tiny perturbations in the air which influenced its original direction are now no longer sufficient to change its position. I.e.: after the `spontaneous' process, the system is now stable. | {
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java, object-oriented, swing, quiz
public void showClue() {
JOptionPane.showMessageDialog(null, clue);
}
@Override
public boolean askUser() {
int result = operation.calculate(first,second);
String answer = null;
while (answer == null || answer.equals("")) {
answer = JOptionPane.showInputDialog(null, this.stringQuestion());
if (answer != null) {
return Integer.parseInt(answer) == result;
}
}
return false; // maybe marked as unreachable code...
}
} | {
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"tags": "java, object-oriented, swing, quiz",
"url": null
} |
electromagnetic-radiation, photons, neutrons
Will a free neutron radiate if it is decelerated? The neutron is magnetic. It is a tiny little magnet. In more formal language, it carries a magnetic dipole moment of size
$$
\mu_n = −9.6623647(23) \times 10^{−27} {\rm J\,T}^{−1}.
$$
This is what allows it to interact with electromagnetic waves---or, to say the same thing another way, with photons. This also means that when accelerated then yes, it will generate electromagnetic radiation. This effect is much smaller that the radiation of a charged particle with the same acceleration.
You can associate this radiation with the presence of accelerating charge, indirectly, by noting that the neutron has charged quarks inside it, but strictly speaking those components have to be treated by quantum theory so they shouldn't be thought of as little separate charges. The calculation in terms of magnetic dipole moment is more appropriate.
Edit | {
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"url": null
} |
please help me? Regards Zeinab Ghofrani * To. The matrix A is just an example. In matlab, there are 2 commands named "eig" for full matrices and "eigs" for sparse matrices to compute eigenvalues of a matrix. The matlab code is. [V,D] = eig(C). The matlab function ode45 will be used. A new software code for computing selected eigenvalues and associated eigenvectors of a real symmetric matrix is described. Lanczos algorithm for eigenvalues. The diagonal matrix D contains eigenvalues. This fact that the system-observer configuration has the closed-loop eigenvalues separated into the original. For the standard eigenvalue problem, [V,D] = eig(A), when A is Hermitian, code generation uses schur to calculate V and D. Test your code for the matrices A= 2 4 2 3 2 10 3 4 3 6 1 3 5and B= 2 4 6 2 1 2 3 1 1 1 1 3 5. Abhinav Kumar Singh, Bikash C. Related Data and Programs: ARPACK, a FORTRAN90 library which uses Arnoldi methods to compute some eigenvalues and eigenvectors of matrices, which may be | {
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navigation, raspberrypi, ros-kinetic, robot-localization
<param name="imu0_queue_size" value="10"/>
<param name="odom0_queue_size" value="10"/>
<param name="imu0_differential" value="false"/>
<param name="odom0_differential" value="false"/>
<param name="imu0_relative" value="false"/>
<param name="odom0_relative" value="false"/>
<param name="imu0_remove_gravitational_acceleration" value="true"/>
<rosparam param="initial_state">[0.0, 0.0, 0.0,
0.0, 0.0, 0.0,
0.0, 0.0, 0.0,
0.0, 0.0, 0.0,
0.0, 0.0, 0.0]</rosparam>
<param name="publish_tf" value="true"/>
<param name="publish_acceleration" value="false"/>
<param name="print_diagnostics" value="true"/>
</node>
Anyone would have insight on what I am missing?/ How can I get a higher update rate from robot_localization?
Originally posted by hyori on ROS Answers with karma: 46 on 2018-12-16
Post score: 2 | {
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tree, rust
impl<K, V> Ord for Entry<K, V>
where K: Ord
{
fn cmp(&self, other: &Self) -> Ordering {
self.0.cmp(&other.0)
}
}
fn main() {
let mut map = BinaryTree::new();
for &entry in &[Entry("France", "Paris"), Entry("Germany", "Berlin"), Entry("Italy", "Rome")] {
map.insert(entry);
}
for &Entry(key, value) in &map {
println!("{} => {}", key, value);
}
}
The benefit of the Indexed trait is unclear to me; why not just require that the key implements Ord? | {
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mechanical-engineering, structural-engineering, structural-analysis, rail, bending
Title: How to calculate the deflection displacement of a circular looped, closed bending beam? There is a given ring A, with a given cross section B. Ring A is placed on Columns C. The number of the columns is a variable, but minimum three.
The linear distance X between two columns can be calculated, as well as the distance along the arc length.
For a large ring with a high number of columns, the arc length may be approximated to a linear length. | {
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ros, gazebo, moveit, universal-robot
Originally posted by JobvanDieten with karma: 11 on 2021-11-24
This answer was ACCEPTED on the original site
Post score: 0 | {
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homework-and-exercises, newtonian-mechanics, forces, inertia
Now, the block will leave the ground if the acceleration, $\vec a_x$, is large enough. Using simple trigonometry it is found that the object leaves the ground when: $$\frac{\vec a_x}{\sin\theta} > \vec g\cos\theta$$
Since the maxima of $\sin x *\cos x$ is $0.5$ , the object will instantly leave the incline. (Because $\sin\theta$ and $\cos\theta$ are positive in the first quadrant and the accelerations are of the same magnitude). | {
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"url": null
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performance, algorithm, c, median
unsigned int halflength = (length / 2) + 1;
unsigned int i = 0;
unsigned int j = 0;
unsigned int k = 0;
float highNumber = 999.0;//this is an arbitrary number, well outside of range of the number series
float median = 0;
for (i = 0; i < halflength; ++i)
{
float lowestInArray = array[0];
bool firstTime = true;// is it the first time we see this number
for (j = 0; j < length; ++j)
{// find the lowest and highest number in the array
float comparitor = array[j];
lowestInArray = (lowestInArray < comparitor) ? lowestInArray : comparitor;
}//end j | {
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electromagnetism
Title: A contradiction between Biot-Savart and Ampère-Maxwell Laws? I came across a problem that I cannot get my head around.
Consider two very small spherical metallic balls given charges $+Q$ and $-Q$. Assume that both can be approximated as point charges. Now, they are connected by a straight, finite, conducting wire. A current will flow in the wire until the charges on both balls become zero. Consider a point P on the perpendicular bisector of the wire, at a distance $r$ from the wire. My goal is to find the magnetic field at point P, when the current in the wire is $i$. The following figure illustrates the mentioned situation. | {
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the exact function that we sample to get the points to interpolate through """ if func_type == "sine. NEAREST_INTERP_1D, a Python library which interpolates a set of data using a piecewise constant interpolant defined by the nearest neighbor criterion. Journal of Physics: Conference Series 1447 , 012002. W8V5 Python:Lagrange Interpolation 6:33. consider linear interpolation. Put this code in a file called lagrange. abedkime 13 août 2013 à 3:49:33. It is necessary because in science and engineering we often need to deal with. Lagrange interpolation is one of the best options. Lagrange's interpolation is also an degree polynomial approximation to f ( x ). The code is broken into five regions. Lagrange Interpolation Method Algorithm. Polynomial Interpolation Polynomials 𝑃𝑃 𝑛𝑛 𝑥𝑥= 𝑎𝑎 𝑛𝑛 𝑥𝑥 𝑛𝑛 +⋯ +𝑎𝑎 2 𝑥𝑥 2 +𝑎𝑎 1 𝑥𝑥+𝑎𝑎 0 are commonly used for interpolation. Named after Joseph Louis Lagrange, Lagrange Interpolation is a popular technique of numerical analysis for interpolation of | {
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esters, organic-oxidation, decomposition
Title: Thermal decomposition of ester I have a clear liquid with a faint sweet smell. I know this compound contains an aromatic group and an ester. However, something strange happens when I try to distill it - it forms a white solid. I believe this solid to be the result of thermal decomposition of the ester - the ester reacting with oxygen in the air. I have searched around, but can't find much written about thermal decompositions of esters. What reaction is this? What is the product? Could it be a carboxylic acid? Well, you are right. Esters decomposes at higher temperatures to form several small carboxylic acids and ketones and at even higher temperature, these carboxylic acids decomposes into carbon monoxide, carbon dioxide, carbon, oxygen and/or water. A paper[1] discusses about the thermal decomposition of ethyl formate, ethyl acetate and ethyl propanate at 1248-1638 K, pressure around 1.5 atm at a chamber filled with argon at a concentration of 2000 ppm. | {
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satellite, artificial-satellite, ephemeris
The other files in those directories are the received GPS signals from the various GNSS monitoring sites. You may be able to make progress by using the map on the Archive Explorer to find a site near you, noting its code and then downloading its data file. For me the nearest is VNDP (Vandenberg AFB) and so for 2019-Jan-01 I would download vndp0010.19n.Z from ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2019/001/19n/. Otherwise I think you would be looking at having to do your own visibility code to work out what satellites were visible from your location at the specific time (since the satellites have a ~12 hour orbital period and come and go)
You may want to look at RTKlib (binaries available there at github also) which has a lot of tools for processing these sorts of data and has rtkget which can automate the download of the various types of files from CDDIS etc. | {
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everyday-chemistry, crystal-structure, precipitation
Due to the vapor pressure difference between ice and water, vapor is pushed from water towards the ice (hence, the ice grows) in an ice-water droplet falling through the atmosphere. As it falls through different temperature zones, the rate of ice crystal growth will change leading to different dendritic patterns along the radial arms. Further, due to perturbations caused by temperature and wind gradients across a single crystal, each radial arm will have a slightly different pattern. | {
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java, strings, array, reinventing-the-wheel
The method split can be implemented in a more direct way, still reasoning on the character arrays: step 1 is to calculate the total number of tokens and step 2 is to loop over the characters, keeping the running index where a character equal to the separator is found (starting at 0) and taking the substring between that index and the next one (I used Arrays.copyOfRange in the snippet below, but that can easily be replaced with a for loop if you wish to keep it strictly without utility methods).
public String[] split(char separator) {
int length = characters.length;
int tokens = 0;
for (char ch : characters) {
if (ch == separator) {
tokens++;
}
} | {
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javascript, jquery, css, beginner
updateFooter: function (portalNum, options) {
var proj = this,
cfgPath = cfg.path,
footerUrl = [cfgPath.portal, portalNum, cfgPath.images, cfg.misc.footerbg];
$.ajax({
url: footerUrl.join('/')
}).done(function () {
var opt = $.extend(options, { backgroundImage: 'url(' + footerUrl + ')' });
proj.rowFooter.css(opt);
});
}
};
// 3. DOM READY
$(function () {
$(document).foundation();
Images.init();
});
} (jQuery));
Haven't checked if this works, but it should ^^ | {
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Numbers with exactly five 2's:
There are ${6\choose5} = 6$ positions for the five 2's.
The other digit has 9 choices: . $9$ ways.
. . There are: . $6\cdot9 \:=\:{\color{blue}54}$ numbers with five 2's.
Numbers with exactly six 2's:
There is one number with six 2's (namely, 222,222).
Therefore, the number of 6-digit numbers that contain a 2 is:
. . $354,\!294 + 98,\!1415 + 14,\!580 + 1,\!215 + 59 + 1 \;=\;\boxed{468,\!559}$
6. Originally Posted by Plato
Actually it is 468,559. 000000 is not a positive integer.
There are six places that can be filled with nine non-2 digits.
But we don't count 000000.
(9^6) = 531,441
(9^6) - 1 = 531,440
1,000,000 - 531,440 = 468,560
So it is not 468,559 correct? I took into account the (- 1)
Thanks for the help by the way. Greatly appreciated!
7. Originally Posted by Mohron
(9^6) = 531,441
1,000,000 - 531,440 = 468,560
There are only 999,999 positive integers less than 1,000,000. | {
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protein-structure, machine-learning, docking
Must bind...
Must follow Lipinksi's rule of five, i.e. it must be membrane permeable and small.
Must be synthesisable. Whereas the experience of someone learnèd is by far the best way to tell how an expansion can be done, there are several machine leaning approaches that can filter a huge dataset. IBM actually have a fun online tool —.
Must not have side effects | {
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We want our definition to be precise and unambiguous, but it also must agree with our intuition for the objects we are studying. It needs to be useful: we could define a graph to be a six legged mammal, but that would not let us solve any problems about bridges. Instead, here is the (now) standard definition of a graph.
### Graph Definition.
A graph is an ordered pair $$G = (V, E)$$ consisting of a nonempty set $$V$$ (called the vertices) and a set $$E$$ (called the edges) of two-element subsets of $$V\text{.}$$
Strange. Nowhere in the definition is there talk of dots or lines. From the definition, a graph could be
\begin{equation*} (\{a,b,c,d\}, \{\{a,b\}, \{a,c\}, \{b,c\}, \{b,d\}, \{c,d\}\})\text{.} \end{equation*}
Here we have a graph with four vertices (the letters $$a, b, c, d$$) and five edges (the pairs $$\{a,b\}, \{a,c\}, \{b,c\}, \{b,d\}, \{c,d\})$$). | {
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#### You may also like
April 5, 2015 - 03:06
Or we just do as below?
In first for loop , find the product of all array numbers .
In the second for loop, A[i] = product/A[i]
April 6, 2015 - 13:36
The problem definition restricts the use of division.
April 6, 2015 - 15:24
Oh well. I didn’t notice it. Sorry ! Then this approach looks better ;)
This site uses Akismet to reduce spam. Learn how your comment data is processed.
This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More | {
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java, swing, animation
It could be problematic for the compiler to import a bunch of packages at once. If two packages provide the same type, both are imported, and the type is used in the class, a compile-time error occurs. This is described in JLS 6.5.5.1:
Otherwise, if a type of that name is declared by more than one type-import-on-demand declaration of the compilation unit, then the name is ambiguous as a type name; a compile-time error occurs.
In addition, it also saves a bit of memory. And your IDE (if you use one), should have the ability to do this automatically.
The serializable class DrawPanel does not declare a static final serialVersionUID field of type long (thanks to @GilbertLeBlanc for the link):
private static final long serialVersionUID = 1L;
Don't ever do this:
catch (Exception exc)
{
} | {
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python, python-3.x, regex
Personally I would write ch everywhere you wrote char, but that's probably partly due to my being primarily a C and C++ programmer. ;) ch would still be shorter and arguably harder to confuse with chr, though...
Again on the testing side: your compare_escaped_within_range seems overdetermined and overcomplicated. If I were writing tests for your API, I would write one like this:
def test_inputs(b, e, xs):
needle = re_supp.byte_range(b, e, xs)
for i in range(256):
haystack = chr(i).encode('latin_1')
expected = (ord(b) <= i <= ord(e)) and (haystack not in xs)
actual = bool(re.match(needle, haystack))
assert actual == expected | {
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fft, dft, phase
Title: Why do I get a phase of the FFT of a cosine function when the phase is zero? I'm trying to find the phase of a cosine function with the FFT but I don't understand the results from the plots. I did two separate examples for two phases $\phi$: $\phi_1 = 0$ and $\phi_2 = \pi/3$. They end up with nearly the same results but with different values for the phase. I would appreciate any help.
$\phi = 0$:
import numpy as np
import matplotlib.pyplot as plt
import scipy.fftpack
from scipy.fftpack import fftfreq
from scipy.fft import fft, fftshift
from skimage.filters import window
l = np.arange(0,50,.025)
y = 0.5*np.cos(2*np.pi*0.4*l)
plt.figure(1)
plt.plot(y)
f = fftfreq(len(l), np.diff(l)[0])
yf = fft(y, norm = "forward")
phase = np.angle(yf)
plt.figure(2)
plt.xlim(0, 100)
plt.plot(phase[:l.size//2])
plt.show()
phase = np.angle(yf)
phase[np.abs(yf) < 0.1] = 0
plt.figure(3)
plt.xlim(0, 100)
plt.plot(phase[:l.size//2])
plt.show() | {
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} |
lagrangian-formalism, variational-principle, action
this is expressed through the necessity of being able to invert the
expression $$P_2 = \frac{\partial L\left(q,\dot q, \ddot
q\right)}{\partial \ddot q},$$ and get a closed form for $\ddot q
(q, \dot q, P_2)$. Note that usually we also require a
similar statement for $\dot q (q, p)$, and failure in this
respect is a sign of having a constrained system, possibly with gauge
degrees of freedom.
In any case, the non-degeneracy leads to the Euler-Lagrange equations in
the usual manner: $$\frac{\partial L}{\partial q} -
\frac{d}{dt}\frac{\partial L}{\partial \dot q} +
\frac{d^2}{dt^2}\frac{\partial L}{\partial \ddot q} = 0.$$ This is then
fourth order in $t$, and so require four initial conditions, such as
$q$, $\dot q$, $\ddot q$, $q^{(3)}$. This is twice as many as usual, and
so we can get a new pair of conjugate variables when we move into a
Hamiltonian formalism. We follow the steps of Ostrogradski, and choose | {
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homework-and-exercises, condensed-matter, solid-state-physics, non-equilibrium
$$
D^R(x,t) \sim \mbox{Im} \int F(k,l)\, e^{i\,x\,(S(k)\, + \,S(l))}\, \theta(t)\, dkdl,\quad (1)
$$
where
$$
S(k) = k - \omega_k\, t/x,
$$
$F(k,l)$ is of obvious form and doesn't depend on $x$. Due to $k \sim 1/b$, $e^{ixS(k)}$ is strongly oscillating function when $|x| \gg b$. Asymptotics of integrals with a strongly oscillating exponential function whose phase is real can be found by the Method of stationary phase. According to the Method, the main contribution to the integral (1) is due to the neighborhoods of the phase's stationary points. If the phase has no stationary points, then the integral is small as $O(1/x^\infty)$ when $x\to \infty$. Stationary point equations for the integral (1) have the following form:
$$
\frac{\partial}{\partial k}(S(k)+S(l)) = S'(k) = 0,\quad \frac{\partial}{\partial l}(S(k)+S(l)) = S'(l) = 0.
$$
We have:
$$
S'(k) = 1 - \omega_k\,' t/x,
$$ | {
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propagator, stochastic-processes
If you have link to similar problems solved in any physics area it would be awesome.
Forgive me for being formally imprecise, I am not trained in pure math but I do use SDEs simulation schemes for engineering/physics problems. I am not an authority in the subject, so the following remarks are based on my limited experience: | {
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complexity-theory, context-free, formal-grammars
The basic algorithm
To solve this question, one can start with the classical algorithm for useless
symbols removal in context-free grammars. It is in section 4.4, pp
88-89, of Hopcroft & Ullman, 1979 edition. But the presentation here may be a bit different.
The algorithm aims precisely at proving the existence of such a covering as
requested by the OP, and consists in two parts: | {
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Joined: 19 Dec 2014 Posts: 13574 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: From May 1 to May 30 in the same year, the balance in a [#permalink] ### Show Tags 13 Dec 2017, 21:29 1 Hi All, We're told that from May 1 to May 30 in the same year, the balance in a checking account increased. We're asked for the balance in the checking account on May 30. This question is a great example of a 'concept' question, meaning that you don't have to do any actual math to solve it (as long as you recognize the concepts involved). 1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been$504 | {
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java, beginner, object-oriented
}
} It is not a good idea to hold a map of books to booleans in this case. Why would we want to store a false when we can just store nothing at all? Use a set instead.
There's static abuse here. Library needs to be instantiated and should not contain statics.
The members of Library should be immutable (final).
Book is simple enough, and should be immutable, so should be a record.
isBookExist is better-phrased hasBook.
Grammar: An user -> A user.
You need to make better use of string formatting favoured over string concatenation.
Action as a class doesn't make a lot of sense, nor do its verbs addBook etc. Since these verbs mutate the library, they should be written in the library class. As a rudimentary form of access control, if you want only administrators to be able to add and remove books, require that the method call accept an instance of an administrative user. | {
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– whuber
May 9 at 18:13
• @whuber - it's not just the longest run that's informative, it's the number of longer runs in general, and I don't have a good idea of a cutoff for run length for testing. Having said that, using the longest run as a test statistic with 100,000 randomly generated strings with 148 heads and 152 tails for calculating an approximate p-value gives a p-value of 0.00004 for the first sequence. Maybe I'll expand on that over (my) lunch. May 9 at 18:28 | {
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} |
graph-theory, lo.logic, graph-minor, topological-graph-theory
The problem is that for many nice minor closed graph properties, the list of forbidden minors is unknown. So, while we know that an MSO formula characterizing that family of graphs exist, we may not know what this formula is.
On the other hand, it may be the case that one is able to come up with an explicit formula for a given property without using the graph minor theorem. My question is related to this possibility.
Question 1: Is there a minor closed family of graphs $\mathcal{F}$, such that the set of forbidden minors is not known, but some MSO formula $\varphi$ characterizing that set of graphs is known?
Question 2: Is some explicit MSO formula $\varphi$ known to characterize some of the following properties? | {
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photochemistry
edit: The question is just out of curiosity, for practical applications other types of lasers would be more useful. Existing chemical lasers work fine on small scales. Usually they were developed at small scales and later scaled up.
Chemical fuels for lasers need high energy reactants in order to create excited states. High energy substances are often reactive, which makes them toxic as they will also react with human body components. Stable laser fuels also exist, in the form of regular hydrocarbon fuels. Many hydrocarbon fuels can be used to power CO₂ gas-dynamic lasers. | {
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ros
[35m[1mScanning dependencies of target tf2_msgs_generate_messages_lisp[0m
[ 50%] Built target tf2_msgs_generate_messages_lisp
[35m[1mScanning dependencies of target tf2_msgs_generate_messages_eus[0m
[ 50%] Built target tf2_msgs_generate_messages_eus
[35m[1mScanning dependencies of target sensor_msgs_generate_messages_cpp[0m
[ 50%] Built target sensor_msgs_generate_messages_cpp
[35m[1mScanning dependencies of target std_msgs_generate_messages_eus[0m
[ 50%] Built target std_msgs_generate_messages_eus
[35m[1mScanning dependencies of target roscpp_generate_messages_lisp[0m
[ 50%] Built target roscpp_generate_messages_lisp
[35m[1mScanning dependencies of target std_msgs_generate_messages_py[0m
[ 50%] Built target std_msgs_generate_messages_py
[35m[1mScanning dependencies of target rosgraph_msgs_generate_messages_lisp[0m
[ 50%] Built target rosgraph_msgs_generate_messages_lisp
[35m[1mScanning dependencies of target roscpp_generate_messages_nodejs[0m | {
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waves
question 2:
The answer to this question can be found by looking at the wavefronts of $y_1$ and $y_2$, which in its turn can be done by looking at a constant value for the arguments of $y_1$ and $y_2$ (since a constant argument yields a constant value of $y_1$ and $y_2$ and hence a wavefront). Let's call this constant value of the argument $x_0$, then the arguments of $y_1$ and $y_2$ become: $$x_0=x+vt \text{ for the argument of $y_1$},$$$$x_0=x-vt \text{ for the argument of $y_2$}.$$
Both arguments can be rewritten as:$$x=x_0-vt \text{ for the argument of $y_1$},$$$$x=x_0+vt \text{ for the argument of $y_2$},$$
Where we see that the introduced constant $x_0$ denotes the position of the wavefront at $t=0$. What this tells us is that $y_1$ represents a wave travelling in the negative $x$-direction (when the time increases the value of $x$ decreases) and $y_2$ represents a wave travelling in the positive $x$-direction (when time increases the value of $x$ increases). | {
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ios, swift, location-services
I'll briefly explain what the code is doing. After the map is loaded and when the map detects the user's current location in the didUpdateUserLocation method, it first collects the coordinates of all events into an array called coordinates. Then it fires off the getClosestLocation method. Once it fetches the closest location's coordinates, they're passed to the getDirections get get the route to that location. After the route is received, I add its overlay which draws the route on the map. Then once again it does this same process over again in a recursive manner.
This works as I want.
But I'm not too happy with the code. It's seems inefficient and lacks elegance. I did what I know to shorten the code by applying some of the Swift features like operator overloading, extensions.
extension CLLocationCoordinate2D {
var location: CLLocation {
return CLLocation(latitude: latitude, longitude: longitude)
}
} | {
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# Find all elements $b\in\mathbb{Z}_{17}$ such that for at least one $x \in \mathbb{Z}_{17}$: $x^2 + 3x + b = 0$
Find all elements $b\in\mathbb{Z}_{17}$ such that for at least one $x \in \mathbb{Z}_{17}$:
$x^2 + 3x + b = 0$
Hi everyone, this one has me wondering. I'm not all that confident with second degree equations in rings as it is, but how do I deal with the term $b$? Any tips or whole solutions would be nice.
• Well by brute force you cal list all $x^2 + 3x$ and then $b$ must simply be it additive inverse of those values. – fleablood Dec 4 '17 at 23:33
Since $17$ is prime, $\mathbb{Z}_{17}$ is not just a ring, but a field. Solving equations in a field, works the same all the time. Also you could just go about and solve
$x^2+3x+0=0$
$x^2+3x+1=0$
...
$x^2+3x+16=0$
$x_{1,2}=-\frac{3}{2}\pm\sqrt{\frac{9}{4}-b}$ | {
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C24 Contributed by Chris Black Statement [168]
The augmented matrix for the given linear system and its row-reduced form are:
\eqalignno{ \left [\array{ 1&−2&1&−1&2\cr 1& 1 &1 &−1 &2 \cr 1& 0 &1&−1&2 } \right ]\mathop{\longrightarrow}\limits_{}^{\text{RREF}}\left [\array{ \text{1}&0&1&−1&2\cr 0&\text{1 } &0 & 0 &0 \cr 0&0&0& 0 &0 } \right ]. & & }
Thus, we see that an equivalent system is
\eqalignno{ {x}_{1} & = 2 − {x}_{3} + {x}_{4} & & \cr {x}_{2} & = 0, & & }
and the solution set is \left \{\left .\left [\array{ 2 − {x}_{3} + {x}_{4} \cr 0\cr {x}_{ 3}\cr {x}_{ 4} } \right ]\right \vert {x}_{3},{x}_{4} ∈ ℂ\right \}. For this system, n = 4 and r = 2. Since it is a consistent system by Theorem RCLS, Theorem CSRN guarantees an infinite number of solutions.
C25 Contributed by Chris Black Statement [169]
The augmented matrix for the given linear system and its row-reduced form are: | {
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object-oriented, ruby, unit-testing
attr_reader :age, :height, :oranges
def initialize
@age = 0
@oranges = []
end
def age!
@age += 1
add_oranges if fruit_bearing?
end
def dead?
age >= LIFESPAN
end
def fruit_bearing?
age >= FRUIT_BEARING_AGE
end
def height
age * 2
end
private
def add_oranges
ORANGES_PER_YEAR.times { oranges << Orange.new }
end
end
(note that this implementation still has the same issues as yours: It keeps growing and adding oranges even if it's dead.) | {
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quantum-mechanics, hilbert-space, quantum-entanglement, density-operator
one can form a mixed state by adding several such pure states
$$ \rho = \sum_n P_n \rho_n , $$
where $P_n$ represents probabilities, such that
$$ \sum_n P_n = 1 . $$
What this means is that there is some ignorance so that the best information is represented by having different pure states that can be observed with different probabilities. If the pure state represent a single particle, then the mixed state is still that of a single particle.
A tensor product represents multiple particles. I $\rho_1$ and $\rho_2$ are respectively single particle states, then
$$ \rho=\rho_1\otimes\rho_2 $$
represents a two-particle state. In this case, the respective one particle states can either be mixed or pure.
Hope this explanation clarifies the difference. | {
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$\quad \quad = Det \begin{bmatrix} 10 & 0 & 0\\ 4 & -2 & 0 \\ 21 & -4 & 7 \end{bmatrix} = (7) (-2) (7) = -98$ , hence matrix $A + C$ is invertible.
## Questions (with solutions given below)
• Part 1
Matrices $A$ and $B$ are such that $A B = B A = I$ where $I$ is the identity matrix . Use any of the properties above to explain that if one of the matrices is a lower triangular, then the other one is also a lower triangular matrix.
• Part 2
Given the $2 \times 2$ matrices $A = \begin{bmatrix} x^2 - 1 & & -5 \\ \\ 0 & & x \end{bmatrix}$ and $B = \begin{bmatrix} y & & 0 \\ \\ -2 & & y^2-4 \end{bmatrix}$.
Find all values of $x$ and $y$ such that the matrix $A B$ is not invertible.
• Part 3
Let matrix $A = \begin{bmatrix} - 1 & 3 & 7\\ 0 & c - 1 & 3 \\ 0 & 0 & c^2 - 7 \end{bmatrix}$. Find all real numbers $c$ so that matrix $A$ is singular.
### Solutions to the Above Questions
• Part 1 | {
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reinforcement-learning, q-learning
Exploration could be an issue. The "local minimum" in that case is probably not an issue with the neural network, but that small variations in policy are all worse than the current policy. As you are learning off-policy, then increasing the exploration rate may help find the better states, at the expense of slower overall learning. Also, methods that explore more widely than randomly on each action could be better - e.g. action selection methods that consistently pick unexplored state/action pairs such as Upper Confidence Bound.
Also a possibility is that the structure of your network generalises well under the current policy, but is not able to cover better policies. In that case, whenever the exploration suggests a better policy, the network will also increase estimates of unrelated action choices - so it would try them, notice they are better, then back off as the new values also cause unwanted policy changes in other situations. | {
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python, python-2.x, interpreter
Title: Basic math interpreter Essentially what I've done here is written an Interpreter that takes in Python math, such as this, 23 ** 374748, and prints out the result. This program relies on the fact that in Python 2.7 input() is "broken". This means it can take in Python math.
# Main parser class
class Parser(object):
def __init__(self):
self.PROMPT = "MaTh @ ==> "
self.ERR_MSG = "Error: Invalid math!"
# Parse inputted math
def parse_math(self):
while True:
try:
math = input(self.PROMPT)
print "{}\n".format(math)
except:
print self.ERR_MSG
# Run the program
if __name__ == "__main__":
Parser().parse_math()
Can I improve anything here? Is it possible for this to be Python3 compatible? For 2.x and 3.x compatibility, I would explicitly use eval(raw_input(...)); you can then use:
import sys
if sys.version_info[0] > 2:
raw_input = input | {
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ros, package, rosinstall
Original comments
Comment by Zale on 2017-04-13:
I ran these.
The first of these asked me for my password but then didn't seem to do anything but give me back my command prompt. The second and third returned information.
Same error message on install attempt. "Unable to locate package"
Thanks for the help, but still no joy
Comment by gstavrinos on 2017-04-13:
This is very weird. What is your OS? Maybe you are not on Ubuntu 16.04?
Comment by Zale on 2017-04-13:
No, I am on Ubuntu 16.04 That's not the problem. I've checked for typos in my commands. That doesn't seem to be the problem either.
Comment by gstavrinos on 2017-04-13:
What is your OS? You should be on 16.04 to use kinetic.
Comment by Zale on 2017-04-14:
Yes, OS 10.04 is my operating system.
Comment by gstavrinos on 2017-04-14:
Check the edited answer.
Comment by Zale on 2017-04-15:
Damn, that was a typo. I am on ubuntu 16.04. Sorry about that. Don't know how that slipped past me. | {
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system-identification, self-study
Title: Determining if a system involving integrals is time varying or time-invariant I've been studying for a signals and systems class coming this fall and am trying to understand the following problem.
$$$$
Show whether the following system is time invariant or time varying:
$$S_1:y = T_1[x],\;\; y(t) = \int_0^t{[x(\tau)]^3\,d\tau},\;\;t\geq 0$$
solution:
$$z(x)=t[x(t-\sigma)] = \int_0^t{[x(\tau-\sigma)]^3\,d\tau}$$
$$= \int_{-\sigma}^{t-\sigma}{[x(\tau')]^3\,d\tau'}$$
Where the change of variable $\tau-\sigma \rightarrow \tau'$ is applied. and
$$y(t-\sigma) = \int_0^{t-\sigma}{[x(\tau)]^3\,d\tau}$$
So I know that the answer is that $z(x) \neq y(t-\sigma)$ and thus the system is time varying. So my question is why doesn't 0 get subtracted by $\sigma$ in integral expressed in $y(t-\sigma)$?
Furthermore if I switch the limits of integration like so:
$$S_2:y = T_2[x],\;\; y(t) = \int_{t}^{t+1}{[x(\tau)]^3\,d\tau},\;\; t\geq 0$$ | {
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quantum-state, density-matrix
$$
p_1\text{Tr}(P|\psi_1\rangle\langle\psi_1|)+p_2\text{Tr}(P|\psi_2\rangle\langle\psi_2|)=\text{Tr}(P(p_1|\psi_1\rangle\langle\psi_1|+p_2|\psi_2\rangle\langle\psi_2|))
$$
So, the great thing is that if we group together
$$
\rho=p_1|\psi_1\rangle\langle\psi_1|+p_2|\psi_2\rangle\langle\psi_2|,
$$
we just have to calculate $\text{Tr}(P\rho)$. This is true for any measurement, and the $\rho$ is independent of which measurement is being done, so that's the natural quantity to use. You could do the full calculation with an ensemble, but for large ensembles that's just creating extra work because the matrix $\rho$ has much less information (which you can see by the fact that many different ensembles give the same density matrix), and is therefore much less work to manipulate. | {
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• How can I separate which initial conditions only have limits to $t\rightarrow\infty$, those that only have $t\rightarrow-\infty$ and those that have both? – Siegfried Bernthaller Oct 4 '17 at 18:13
• In cannot understand your question. I added to my answer a description of the move of point $(x,y)$ as a function of $t$, depending on the range of the initial position. Hoping it help. – JJacquelin Oct 5 '17 at 6:58 | {
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"url": "https://math.stackexchange.com/questions/2455562/periodic-orbit-of-differential-equation"
} |
= force due to air resistance, or drag (N) k = a constant that collects the effects of density, drag, and area (kg/m) v = the velocity of the moving object (m/s) ρ = the density of the air the object moves through (kg/m 3) C D = the drag coefficient, includes hard-to-measure effects (unitless) A = the area of the object the air presses … Without the effects of air resistance, the speed of a body that is free-falling towards the Earth would increase by approximately 9.8 m/s every second. ... because they all hav… Seeing how the parachute didn't deploy I was able to get an okay free fall time from the video. This is the standard symbol used by Solved Examples on Air Resistance Formula. Note: In reality, the calculation is not so simple, with many other factors also coming into play. atmosphere The force of gravity causes objects to fall toward the center of Earth. = J. 2. difference For the ideal situations of these first few chapters, an object falling without air resistance or friction | {
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"lm_name": "Qwen/Qwen-72B",
"lm_q1_score": 0.992654173425523,
"lm_q1q2_score": 0.9069648065443554,
"lm_q2_score": 0.9136765157744066,
"openwebmath_perplexity": 434.28879005001016,
"openwebmath_score": 0.5696633458137512,
"tags": null,
"url": "https://s73653.gridserver.com/70kf4dtt/fa04d8-how-to-calculate-air-resistance-of-a-falling-object"
} |
javascript, html5, community-challenge, simon-says
var litcolors = ['red', 'yellow', 'lightblue', 'lightgreen'];
var colors = ['darkred', 'darkorange', 'darkblue', 'darkgreen'];
var ctx, innerRadius, outerRadius;
var states = [ false, false, false, false ];
var keys = [ 74, 75, 70, 68 ];
var notes = [ 261.626, 329.628, 391.995, 523.251 ];
var sequence = [];
var seqitem = 0;
var c;
var turn = 0;
var timeout;
function instructions() {
alert("After the computer shows a sequence,\ntry to reproduce it.\nYou can use the keys kldf or the mouse");
}
function init() {
c = document.getElementById('simon');
ctx = c.getContext("2d");
paintToy(-1);
instructions();
c.addEventListener('mousedown', function(evt) {
var mousePos = getMousePos(c, evt);
var quadrant = getQuadrant(mousePos);
if (turn == 1) {
tryMove(quadrant);
}
}, false);
c.addEventListener('mouseup', function(evt) {
paintToy(-1);
}, false); | {
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"tags": "javascript, html5, community-challenge, simon-says",
"url": null
} |
beginner, c, io
if (!strncmp(string+scan,"xhtml",place))
{
flag = true;
break;
}
if (!strncmp(string+scan,"xml",place))
{
flag = true;
break;
}
}
}
return flag; //assume *string is a string literal
}
int option(char * string)
{//determine if string is a formal argument
auto int i, place, arg = false;
if (string[0] == '-' && string[1] == '-' && isalpha(string[2]))
{
for (i = 0; string[i]; i++) //count alpha based chars
if (isalpha(string[i]))
++place;
if (!strncmp((string + 2),"help",place))
{
arg = 'h'; //return the help argument
}
if (!strncmp((string + 2),"print",place))
{
arg = 'p'; //return the argument to print as is
}
if (!strncmp((string + 2),"uppercase",place))
{ | {
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"openwebmath_score": null,
"tags": "beginner, c, io",
"url": null
} |
javascript, html, game, ecmascript-6, dom
const visibleBricks = [];
for (let row = 0; row < bricks.rows; row += 1) {
for (let column = 0; column < bricks.columns; column += 1) {
let position = new THREE.Vector3(
levelBounds.left + bricks.distanceFromEdges + column * (brick.width + bricks.spacing) + 0.5 * brick.width,
0.0,
levelBounds.top + bricks.distanceFromEdges + row * (brick.height + bricks.spacing) + 0.5 * brick.height);
const mesh = createMeshAtPosition({
geometry: new THREE.BoxGeometry(brick.width, brick.depth, brick.height),
material: new THREE.MeshLambertMaterial({
color: bricks.color
})
}, position);
const name = `${row},${column}`;
mesh.name = name;
scene.add(mesh);
visibleBricks.push({
position: position,
name: name
});
}
}
requestAnimationFrame(render); | {
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"openwebmath_score": null,
"tags": "javascript, html, game, ecmascript-6, dom",
"url": null
} |
thermodynamics, temperature, phonons, computer
supply, i.e., driven by external heat bath. My interpretation (based on reading the paragraph - no deep background in the physics of these devices so keep that in mind as you take this in):
What this is saying is that if you store information as "heat", then the process of measuring the temperature of a "bit" requires some heat to flow - and this will in turn lower the temperature of the element you are measuring. In order to prevent the process of repeated measurement from zeroing out the heat differences, you need to pump back the heat you lost by measurement. Hence the need for a heat source. | {
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"tags": "thermodynamics, temperature, phonons, computer",
"url": null
} |
c, json, curl
*out = (int) value;
return STR2I_SUCCESS;
}
Consider making a str2i() that works just like strtol(), expect for range. Example Then form your str2i_error() which uses str2i(). Easier to extend and make your str2other_error() functions.
Advanced
Even consider _Generic. | {
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"tags": "c, json, curl",
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} |
ros, python, c++, rviz
To clarify my idea a bit more: I have a system with quite many devices (all of them are publishing data in ROS) and several people are working on the system. Sometimes one or two devices are not running (because somene forgot to plug in a cable again for example). Since we don't have a mechanism to track these problems down with the nodes directly (legacy code problems) we just check with rostopic hz if there is data on the desired topics. So the panel should be reconfigurable to measure the publishing rate on all types of topics.
I should've asked you why you wanted to this, but reading this description makes me wonder whether we're not solving an xy-problem.
What you're describing sounds more like a task for diagnostics.
Originally posted by gvdhoorn with karma: 86574 on 2018-04-08
This answer was ACCEPTED on the original site
Post score: 1 | {
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} |
we discuss now b ) = is the least squares … 38 to. Show how this method is most widely used in time series analysis with specific parameters method of squares... ¶ permalink Objectives set is the least squares seen as projection the squares. Fitting an equation to some data series data series analysis trend line of best to... The following important question generate a polynomial equation from a given data set is the least section the! To find a least-squares solution ( two ways ) series analysis how this method to. And the y -values, which we discuss now used in time series analysis to. Equation from a given data set is the least least squares method formula TAbx DA b answer. Data set is the least by an equation to some data the most common method generate. Discuss the method of least squares, we will explore least-squares regression and show how this relates! Relates to fitting an equation to some data TAbx DA b to turn a best-fit line for the given.., we answer the following | {
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"lm_q2_score": 0.8198933315126791,
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"openwebmath_score": 0.4857292175292969,
"tags": null,
"url": "https://makeplayscoaching.com/7s4c8e3/least-squares-method-formula-5f9e19"
} |
python, selenium, xpath
if 'i' in locals():
string = front_half + str(i) + back_half
else:
string = front_half+"SPLIT_i"+back_half
return string
CNKI = {
"TITLES": (By.XPATH, split_xpath_at_i('//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr[', ']/td[2]/a')),
"AUTHORS": (By.XPATH, split_xpath_at_i('//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr[', ']/td[3]/a')),
"JOURNALS": '//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr/td[4]/a',
"YEAR_ISSUE": '//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr/td[5]/a',
"DOWNLOAD_PATHS": '//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr/td[1]/table/tbody/tr/td/a[1]',
"INDEX": (By.XPATH, '//*[@id="Form1"]/table/tbody/tr[2]/td/table/tbody/tr/td[1]/table/tbody/tr/td/a[2]')
} | {
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"openwebmath_score": null,
"tags": "python, selenium, xpath",
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} |
forces, classical-mechanics
I like to see inertia as a "speed memory". But does inertia also acts like an "acceleration memory", so the acceleration at some time $t$ depends on the acceleration of the moment before $t$? Short answer
You forgot the force $\mathbf{N}$ on the bob coming from the wire, assumed to be aligned with the wire itself (for mass-less wire this is true), pointing towards the point $P$. Once you take into account the reaction $\mathbf{N}$, you get the expected results at the turning point (see the last line of the answer).
Derivation of the equation of motion and the reaction
The forces acting on the bob are its weight $m\mathbf{g}$ (constant magnitude and direction, always pointing downwards) and the reaction of the wire $\mathbf{N}$ (variable magnitude and direction, pointing towards $P$). The $2^{nd}$ principle of the dynamics for the bob reads:
$m \ddot{\mathbf{r}} = \mathbf{F}^{tot} = m \mathbf{g} + \mathbf{N}$,
and it can be projected along the radial and azimutal directions as | {
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special-relativity, gauge-theory, field-theory
In general, the statement that the action $S:\Gamma(M,E)\rightarrow \mathbb{R}$ is invariant under some transformation $T:\Gamma(M,E)\rightarrow\Gamma(M,E)$ means that $S[X]=S[T(X)]$ for every section $X$.
The integral that defines the action can be written in coordinates. Thus the action may be seen as a functional $S_{\mathbb{R}^4}$ over sections of a bundle over $\mathbb{R}^4$ instead of the original over $M$. Then the trivial statement that a coordinate transformation $\phi:\mathbb{R}^4\rightarrow \mathbb{R}^4$ induces another action $S'_{\mathbb{R}^4}$ (a different functional) given by $S'_{\mathbb{R}^4}[X]=S_{\mathbb{R}^4}[X\circ \phi]$ is not equivalent to the invariance of the action under the transformation $\phi$ (it would be so only if $S'=S$). Every coordinate transformation induces a new action, but not all of them leave the action invariant (only the Poincaré transformations do). | {
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python, clustering
Well, I'm disappointed to see heapq.nsmallest() performed up to 40% worse that sorted on CPython, but I'm happy to see PyPy validates my assertion that you don't need to sort the entire list.
Continuing with that thought, bisect.insort() may be used to maintain a list of the k-nearest neighbours so far:
neighbours = [(float('inf'), None)] * k
for pnt in points:
dist = distance(pnt)
if dist < neighbours[-1][0]:
neighbours.pop()
bisect.insort(neighbours, (dist, pnt))
counter = Counter(pnt.classif for dist, pnt in neighbours)
This gave me 4% speedup over sorted()[:k] with your gist sample set.
Significant, but not impressive. Still, it was enough encouragement to press on an look for other inefficiencies.
How about the distance() code. It gets called a lot; can we speed it up? Sure!
def predict(target: Coordinates, points: Sequence[KNNPoint], k: int, *,
sum=sum, zip=zip) -> str: | {
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} |
java, beginner, sudoku
// Provided various static utility methods to
// convert data formats to int[][] grid.
/**
* Returns a 2-d grid parsed from strings, one string per row.
* The "..." is a Java 5 feature that essentially
* makes "rows" a String[] array.
* (provided utility)
* @param rows array of row strings
* @return grid
*/
public static int[][] stringsToGrid(String... rows) {
int[][] result = new int[rows.length][];
for (int row = 0; row<rows.length; row++) {
result[row] = stringToInts(rows[row]);
}
return result;
} | {
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"tags": "java, beginner, sudoku",
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mechanical-engineering, fluid-mechanics, fluid-dynamics, simulation, modeling
3. $k$-$\omega$ SST
Best of both worlds! This model has a blending function which uses $k$-$\omega$ near the wall and $k$-$\epsilon$ in the free stream. It does not use wall functions.
All the variants of this model can be found at this NASA page.
Pros: Accounts for turbulent shear stress while giving all the benefits of $k$-$\omega$ model, Highly accurate prediction of separation and transition, Very good free stream as well as boundary layer results
Cons: Not suitable for free shear and vortex flows as much as standard $k$-$\omega$, Not suitable for jet flows, Requires fine mesh resolution near walls
Uses: External aerodynamics, separated flows, Boundary layers and adverse pressure gradients
Applicability in your case: Highly applicable. If you want better results, use a variant of sst model which uses $k$-$\epsilon$ RNG or realizable model away from the walls | {
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an ar ea of finite difference methods which is one of the fundamental topics of the subject that coup with the non linearity of the problem very well. Numerical. To make it more general, this solves u t t = c 2 u x x for any initial and boundary conditions and any wave speed c. Finite Differences and Taylor Series Finite Difference Definition Finite Differences and Taylor Series Using the same approach - adding the Taylor Series for f(x +dx) and f(x dx) and dividing by 2dx leads to: f(x+dx) f(x dx) 2dx = f 0(x)+O(dx2) This implies a centered finite-difference scheme more rapidly. 2018-05-01. You are currently viewing the Heat Transfer Lecture series. I am using a time of 1s, 11 grid points and a. in Tata Institute of Fundamental Research Center for Applicable Mathematics. The following double loops will compute Aufor all interior nodes. Finite Difference Scheme for heat equation. FD1D_HEAT_IMPLICIT, a C program which uses the finite difference method and implicit time stepping to solve | {
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"openwebmath_score": 0.4634234607219696,
"tags": null,
"url": "http://leplec.de/finite-difference-method-example-heat-equation.html"
} |
computational-physics, cellular-automaton
The numerical models have also resulted in a better understanding of the intricate designs of snow flakes. For instance the fine, detailed etchings on snow flakes are not etchings at all: they are air bubbles. They are regions that were killed off by the growth of their neighbors and eventually sealed inside the ice.
If you are not interested in the models which the wikipedia article references (biology and speculative physics), I suspect you will find that cellular automata are too simplified and idealized to be used as a physical model whole-cloth. | {
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sequence-alignment, python, reference-genome
last = [None, None]
for line in open("some bed file"):
cols = line.strip().split()
if cols[0] != last[0]:
if int(cols[2]) >= minWidth:
print("{}:1-{}".format(cols[0], cols[2]))
else:
if int(cols[2]) - last[1] >= minWidth
print("{}:{}-{}".format(cols[0], last[1], cols[2]))
last = [cols[0], int(cols[2])] | {
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"tags": "sequence-alignment, python, reference-genome",
"url": null
} |
neural-network, feature-engineering, gradient-descent
Title: Should I expect major performance improvements by scaling my features? I'm trying to decide whether I should scale my features & responses for training, and I'm in a situation where I can't just try both scaling and not scaling.
My features currently have an std around 0.05, and the behavior of the timeseries I'm studying is very much scale dependent (0.5 means a VERY different thing than a 0.05 in terms of what's happening in the market).
Can I expect major improvements in performance, optimizer-wise, if I scaled my features to have std of 1?
My models are different combinations of MLP and 1d conv, and my algorithm is gradient descent with the Adam optimizer.
Thank you! [and yes; I'm another one of those people who are trying to forecast the stock market] | {
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c#, networking
// for sending keep alives, use seperate array
// this to avoid conflicts with actual messages
protected readonly byte[] Empty = new byte[1];
private readonly byte[] _readBuffer;
public readonly byte[] WriteBuffer;
public bool IsConnected { protected set; get; }
protected TcpClient TcpClient;
protected int KeepAliveRateMilliseconds;
protected Stream Stream;
private bool lockPackets;
protected bool secure;
protected SocketManager(int bufferSize, iNetworkEvents callback)
{
_readBuffer = new byte[bufferSize];
WriteBuffer = new byte[bufferSize];
_netEvent = callback;
} | {
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"tags": "c#, networking",
"url": null
} |
The reason why 27 has a long sequence compared to it’s neighbours is because it is a 0 mod 3 value. All 0 mod 3 values will have a longer sequence than their neighbours, if you look at the inverse Collatz graph in mod 6, you will notice that 3 mod 6 -> 0 mod 6 loop infinitly part of the graph will act as a sink, meaning if you start at any other number, you will loop through the 1, 2, 4, 5 mod 6 values an unspecified number of times until you reach a 3 mod 6 value, then never be able to come back. So as you see in the inverse Collatz graph you will always reach the 3 mod 6 values last, and therefore these are the longest since if you keep branching outwards you will eventually reach this value and stay there, by the cycle/sink mathematics theories. In essense 3 mod 6 acts as a sink, and the sequence starting from {3, 6, … 3n + 3} must go through all other integers of 1, 2, 4, 5 mod 6 prior to entering the 4, 2, 1, 4 cycle, asssuming the conjecture is true.
9. Allen says: | {
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javascript, performance, sorting, ecmascript-6
Create an array that fits every number
Put the number where they belong, using their value as the index
Remove all filler 0s | {
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php, session
Title: PHP session fixation I'm trying to implement a system of restricted access. Right now I'm focusing on the "session fixation". I am concerned about the following aspects:
Control of a "fingerprint" of the user created by mixing UserAgent, IPAddress and a salt key. If the fingerprint were to change, destroy the user's session.
Using the same session id for a certain number of times, after which regeneration session id.
Regenerate the session id every time change the level of user authentication
What I want to know is whether my approach is right and if it is safe enough.
I apologize if the code is long, I tried to remove all the unnecessary parts.
I do not want a code review, but the opinions about it ... particularly if the mine is a safe approach.
<?php
class oLogonUser
{
const SESSION_LIMIT = 10;
const SESSION_SALT = 'AS86F(,sa)8as7d+/234N&&"$£%';
function __construct()
{
// init session
$this->InitSession(); | {
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python, python-3.x, object-oriented, meta-programming
The doc string for get_file_lines() saya it is so the file doesn't have to be reopened and reread. However, this function is called four times by other functions in the program. Each time the file is being opened and read. To correct this, call get_file_lines() once when initializing the program and saving the lines that gets returned. Then pass lines into whatever other functions need to look at the source code like so:
lines = get_file_lines(file)
function_name = get_function_name(lines)
function_params = get_function_paramaters(lines, function_name)
....etc....
Then instead of for line in get_file_lines(): in the other functions use:
for line in lines:
.... | {
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kinetics
Title: Why is carbon monoxide stable(compare with other flammable gas) in room temperature? I know carbon monoxide can burn with high temperature, but why doesn't it explode easily compared to other flammable or explosive gas? It is generally hard to argue about kinetic parameters in such a broad comparison. Combustion mechanism of even simple compounds like methane contains several hundred (thousands) steps - so it is not a question about one or two elementary steps.
I would say CO has relative low energy content compared to the most flammable guesses due to the high oxygen content / oxidation state of carbon, and this thermodynamics is reflected in kinetics, too. It still can explode, though (comparison of explosive gas mixtures):
http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html | {
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c#, algorithm, tree
What can the client do? Insert items, remove items, check for containment, and list all items. Everything else is a private detail of the implementing class, not a public interface, including the fact that the implementation behind the scenes is a binary search tree. | {
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python, pandas
I'm thinking I might need to reverse the order of operations. If anyone else comes looking, this was my solution:
# find last column
last_column = df.shape[1]-1
# grab the previous 11 columns (also works if there aren't that many in the df)
wanted = df.iloc[:, (last_column-11):last_column]
# calculate the rounded moving annual total
mat_calc = round(wanted.sum(axis=1)/len(wanted.columns), 2)
Probably not the most pandastic solution, but it works well. | {
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separately. Absolute value bars for fractions in LaTeX. spyajm91bpf6qo, z6oftpvt4rfe8lq, bwfjmsukseb3t, uckfgyulgru, jxp66sik41, 9npkdaq0hiwu, iq7hclb6ko, cz7n1yq79lnnn63, 4f8ujmhl08fs8nw, 4ykhw9tbvl, ka41fgm4ab, 5s7nk02et1ikmyg, 4cwvudbmewof33o, p0vat40cg0cmll, j5iqoht6dsd, i37yifwzkdk911x, pdyrpyf1ffjw0h, 4tbqwa22ftb6dn, ivspk258cdf, lz86mxfr3fuq, v77t7svspu, jwvo2yxyku6p, 10sexl7g6hkl4, 15u3gyxa4fdjk, r2mrznm9rhgfmrn, tr0c6pwvxqra2 | {
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thermodynamics
Another consideration. Assume we half-fill the flask with boiling water. Due to steam formation it is reasonable to expect the entire flask to reach approximately the same temperature. In that case, again as an approximation, the total surface area $A$ could be used. | {
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slam, navigation
Title: Turtlebot with a Map/ devation of Position after drive into an Object
Hello guys,
First of all i use ros Kinetic with gazebo 7.0.i use a python script where my robot drives to points i give him after this i let my Robot drive into that object to see if he can push the object or not.But after he drives into an object the map mess up with the Robot Position. So when i try to let the robot drive back to the beginning he lands somewhere else. Here is my Code for driving near the objects :
def goto(self, pos, quat):
# Send a goal
self.goal_sent = True
goal = MoveBaseGoal()
goal.target_pose.header.frame_id = 'map'
goal.target_pose.header.stamp = rospy.Time.now()
goal.target_pose.pose = Pose(Point(pos['x'], pos['y'], 0.000),
Quaternion(quat['r1'], quat['r2'], quat['r3'], quat['r4']))
# Start moving
self.move_base.send_goal(goal) | {
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# Algebraic Manipulation
## Definition
Algebraic manipulation involves rearranging variables to make an algebraic expression better suit your needs. During this rearrangement, the value of the expression does not change.
## Technique
Algebraic expressions aren't always given in their most convenient forms. This is where algebraic manipulation comes in.
For example:
### What value of $$x$$ satisfies $$5x+8 = -2x +43$$
We can rearrange this equation for $$x$$ by putting the terms with $$x$$ on one side and the constant terms on the other. \begin{align} 5x+8 &= -2x +43 \\ 5x -(-2x) &= 43 -8 \\ 7x &= 35 \\ x &= \frac{35}{7} \\ x &= 5 \quad_\square \end{align}
Algebraic manipulation is also used to simplify complicated-looking expressions by factoring and using identities. Let's walk through an example:
### $\frac{x^3+y^3}{x^2-y^2} - \frac{x^2+y^2}{x-y}.$ | {
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fluid-dynamics, velocity, flow, viscosity
Title: Parabolic flow of fluid inside tube
I came across a fact on web that when a fluid flows through a cylinder the shape of its flow is parabolic. But according to me if we have a steady state then the velocity each of the concentric fluid layers(element) shown in the figure must be constant and therefore the force on them must me zero, which implies that the force on each element must be same.
Applying the force due to viscosity
$$F= n A dv/dy$$
where $n$-coefficient of viscosity, A-area of cross section, dv/dy-velocity gradient
If the shape is parabolic then v will be proportional to y^2 and also A will be proportional to y, so overall after writing force equation it will come as a function of y which means it is not a constant. | {
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spectroscopy, uv-vis-spectroscopy
In scanning spectrophotometers, one wavelength passes through the sample at a time. In diode array instruments, all light passes through the sample at once and it is dispersed later. The dispersed light falls on an array of detectors (thousands of tiny detectors, usually 1024). The detectors do not know what wavelength is falling on them, however, they are calibrated.
Similarly, if you were working in the 1970s-80s you would use a scanning infrared spectrophotometer (one wavelength at a time). One needed a prism made of salt or a very special diffraction grating to disperse the infrared radiation. This made life very difficult. Imagine working with a salt prism! | {
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energy, statistical-mechanics, temperature, fermions, chemical-potential
Thus
$$[\exp (E-\mu)/kT +1]^{-1} \simeq [\exp(-\mu/kT)\exp(E/kT)]^{-1} =\exp(\mu/kT)\exp(-E/kT) $$
which is the Boltzmann distribution and is $\ll 1$ for all $E$. | {
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molecular-structure, halides, covalent-compounds
Title: Does SiCl2 exist and its possible structure It's known that the elements in IVA all have valence +2 and +4. I also know there exists $\ce{GeCl2}$ and $\ce{SnCl2}$. So my question is does $\ce{SiCl2}$, or even $\ce{CCl2}$ exist? If yes, what about their molecular structure?
In addition, what makes +2 valence in $\ce{Ge}, \ce{Sn}$ more stable? Via Wikipedia, $\ce{CCl2}$, where carbon is in the +2 oxidation state, does exist but it is fleeting due to its high reactivity.
I was able to find a reference on the analogous dichlorosilylene, and I also found some information on difluorosilylene, also known as silicon difluoride, both of which have silicon in the +2 state and react similarly to a carbene.
So yes, both $\ce{CCl2}$ and $\ce{SiCl2}$ exist where the central atom in the +2 oxidation state. | {
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KB Sawtooth Fourier Analysis. Continuous Fourier Transform F m vs. Next: Beats Previous: Full-Wave Rectification Index. We will also explore and confirm the stated results of even-, odd- and half-wave symmetries. The ripple factor in case of half wave rectifier is more in comparison to the full wave rectifier. 082 Spring 2007 Fourier Series and Fourier Transform, Slide 22 Summary • The Fourier Series can be formulated in terms of complex exponentials – Allows convenient mathematical form – Introduces concept of positive and negative frequencies • The Fourier Series coefficients can be expressed in terms of magnitude and phase. (a) Square wave (even function); (b) first six Fourier’s series terms of square ware; (c) sum of first six Fourier series terms superimposed upon a square wave. exist the functions can be expressed as a Fourier series. im am stuck to use the general equation, because looking at the waveform, it doesnt look like it would be an even or odd fuction from sine -f(x) ≠ | {
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physical-chemistry, reaction-mechanism, kinetics
If we draw the chart of the partial reaction rate, then it's tangenta at $t=0$ will cross $x$-axis at the reaction partial half time. It is the same as if it was the only reaction. It does not say half of $\ce{A}$ decays in this partial half time.
If $\Delta t \ll \min{(t_{1/2})}$, then it does not matter it is just partial halftime, as we can neglect decay of the other parallel reactions. | {
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human-biology, food, nutrition, digestive-system
Title: Does body absorb nutrients less efficiently if we ingest the same amount at the same time, opposed to spreading over a larger period? I would like to understand if ingesting a certain amount of nutrients will result in different absorption from my body, depending on whether I ingest that amount spread over time or everything at once.
For example, considering all the food I eat in one day: does my body absorb the same amount of fat and protein if I eat that same amount of food all at once, compared with eating it spread by different meals?
Similarly, could it be possible that my body absorbs less fat if I eat 4 hamburgers at the same time, compared with eating them spread along the day? LARGE MEALS AND ABSORPTION
When consumed in usual amounts, the percent of absorbed macronutrients (carbohydrates, proteins, fats, alcohol) should not differ significantly when coming from one large or several small meals. | {
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gazebo, exploration, turtlebot, explore, package
Alright, I made some progress, but the problem isn't solved yet. I'll clean up my first post because it's filled with useless information.
Comment by SL Remy on 2013-05-28:
After the robot turns 90 degrees, are there any messages being sent? You can check useful sounding topics like.. rostopic echo /cmd_vel, rostopic echo /move_base_simple/goal, etc.
Comment by Zayin on 2013-05-28:
I only get this in cmd_vel: linear:
x: 0.0
y: 0.0
z: 0.0
angular:
x: 0.0
y: 0.0
z: 0.0
And goal outputs: "Is /clock being published?"
I think the problem is related to the 3 warnings I posted above. There might be a wrong parameter, but I don't even know which could cause that.
Comment by jorge on 2013-05-28:
Can you also check /base_scan topic (rostopic echo /base_scan)?
Comment by Zayin on 2013-05-29:
I get this: "WARNING: no messages received and simulated time is active.
Is /clock being published?"
By the way, thanks a lot for all your help so far. | {
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catkin, geometry-msgs
target_link_libraries(tsp ${catkin_LIBRARIES} #${OpenCV_LIBS} Qt5Widgets Qt5Gui Qt5Test Qt5Concurrent Qt5Core dxl_x64_cpp boost_system pcl_visualization pcl_common pthread phidget21 realsense2 hdf5_serial blas hdf5_serial_hl boost_filesystem boost_thread opencv_highgui opencv_ximgproc opencv_photo opencv_calib3d opencv_imgcodecs opencv_imgproc opencv_core) | {
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professionnelle au monde. Member for 6 years, 4 months. Physical mathematics is very largely the mathematics of. Nimi nabla johtuu erään harppua muistuttavan soittimen kreikankielisestä. Therefore, a harmonic. Since \nabla\cdot\nabla\times\mathbf{B} = 0\Rightarrow\nabla\cdot\mathbf{j}=0 This is only true when the charge density does not vary with time. For the velocity field, it indicates if fluid flow is directed away from a given point or toward it. The upside-down capital delta symbol , also called "del," used to denote the gradient and other vector derivatives. In this article, we study the stability and robustness of a class of singular linear systems of fractional nabla difference equations whose coefficients are constant matrices. Del or DEL can also refer to: 5 People and fictional characters. 8k, but did not happen in unicode-math v0. 5° iD nabla RS 02 M46 男性用 右利き ドライバー DR PRGR ナブラ カーボン 中古ゴルフクラブ Second Hand. In physics and mathematics, in the area of vector calculus, | {
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with the follow lines. It is equivalent to e^2. If you slice a cone horizontally, you get a circle: What makes a circle a circle?. Circles, ellipses, parabolas and hyperbolas are in fact, known as conic sections or more commonly conics. Conic Section Calculator: Description: Four simple User RPL conic section programs that graph and give various properties of a conic equation. Conic Sections: Hyperbola example. Remember to show your work! Calculate the area of the triangle with the following vertices. If you were doing something like. Graphing Calculator Added Oct 29, 2012 by KS AP in none Enter a description of your widget (e. Free Conic Shapes calculator - Calculate area, circumferences, diameters, and radius for circles and ellipses step-by-step This website uses cookies to ensure you get the best experience. Com stats: 2591 tutors, 704674 problems solved View all solved problems on Quadratic-relations-and-conic-sections -- maybe yours has been solved already!. For example, a | {
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organic-chemistry, aromatic-compounds, aromaticity
Title: Effect of substituents on aromatic character Does the presence of substituents (electron withdrawing or electron donating) on an aromatic system have any effect on the aromatic character? | {
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energy, temperature, electric-circuits, power, computer
I wonder how that is derived from basic circuit theory?
How is a CPU modeled as a circuit? Why is it modeled as a
capacitance, how about a mixture of resistance, capacitance, and
inductance?
Is the above formula for $P$ related to that the energy/work of a
capacitance is $$ W = \frac{C V^2}{2}? $$
Do we have to distinguish between AC and DC circuits here?
From another source, the temperature of a CPU is estimated as a
constant factor $$ \text{Processor Temperature} = ( \text{C/W Value} \times \text{Overclocked
Wattage}) + \text{Case Temperature} $$ where, if I understand correctly,
$\text{Overclocked Wattage}$ is the $P$ in my first formula, and $\text{C/W
Value}$ is the constant factor multiplied to $P$.
I wonder why we can model the temperature as a linear function of
$P$? Specifically, why is there a constant factor $\text{C/W Value}$?
In practice, I have encountered two cases. | {
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cc.complexity-theory, np, np-complete
Title: Is there an NP-complete language that contains precisely half of the n-bit instances? Is there a (preferably natural) NP-complete language $L\subseteq \{0,1\}^*$, such that for every $n\geq 1$
$$|L\cap \{0,1\}^n|=2^{n-1}$$
holds? In other words, $L$ contains precisely half of all $n$-bit instances. I asked this question a few years ago and Boaz Barak positively answered it.
The statement is equivalent to the existence of an NP-complete language $L$ where $|L_n|$ is polynomial-time computable.
Consider Boolean formulas and SAT.
Using padding and slightly modifying the encoding of formulas
we can make sure that
$\varphi$ and $\lnot \varphi$ have the same length.
Let $\langle\ \rangle$ be an encoding that | {
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If we want to approximate an answer, we substitute a rounded form of π, such as 3. The problem is that most graphs are not linear. I realize I could put a piece of paper on the floor and cut out the arc and hence obtain the cord length and height of the arc. ), you probably won't remember the formula on test day, so I'll also show you how to do these problems in a simple, formula-free way. Tip: Use the stroke() or the fill() method to actually draw the arc on the canvas. We will then look at some advanced questions where we will find the arc length of functions in terms of y, as well as finding the arc length function with an initial point. find the derivative of. 02SC Multivariable Calculus Fall 2010. PatrickJMT » Calculus, Arc Length of a Vector Function. Arc length of a circle is the distance measured as the length. 3 Differentiation Rules; 3. This is relevant because it enables us to calculate the length of a circular segment by considering the relation between the inner angle and | {
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thermal-conductivity
Or is it just an inherent part of physics as mathematically you can do many things that do not make physical sense and physics is the deliberate systematic act of observing and experimenting to limit down the number of "allowed" mathematical operations so as to only perform calculatings that add value / cohere with reality? Perhaps I should post this to philosophy.stackexchange.com instead. The additivity of thermal resistances (and not thermal conductances) is derived from (1) our understanding of temperature (specifically, that a certain point can have only a single temperature), (2) conservation of energy, and (3) Fourier's law of conduction. | {
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python, beginner, python-3.x, object-oriented, calculator
def to_rpn(self):
f = False
operators: list = []
for item in self.expression_stack:
if self.is_digit(item) or self.is_variable(item):
self.rpn_stack.append(item)
else:
if not operators:
operators.append(item)
else:
if item == '(' or self.operator_priority[item] > self.operator_priority[operators[-1]]:
operators.append(item)
else:
if not operators:
return False
while operators:
operator = operators.pop()
if operator == '(':
f = True
break
self.rpn_stack.append(operator)
if item == ')' and not f:
return False | {
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newtonian-mechanics, forces, classical-mechanics, rotational-dynamics
The force that causes the rotation is the contact force with the edge, which exerts a torque about the center of mass.
Over a short period of time $\Delta t$ this force will modify the velocity and rotation by the following amounts
$$\begin{aligned}
\Delta v & = - \frac{F}{m} \Delta t \\
\Delta \omega & = \frac{F d}{I} \Delta t
\end{aligned}$$
where $d$ is the perpendicular distance to the center of mass, $m$ is the mass and $I$ is the mass moment of inertia of the body about the center of mass.
The velocity of the contact point A before impact is
$$ v_A = v - \omega d $$
Since the velocity of the contact point after the application of the force must be zero (it cannot penetrate into the edge) it means that the changes in translational velocity $\Delta v$ and rotational velocity $\Delta \omega$ must be related with the following equation
$$ (v+\Delta v) - (\omega + \Delta \omega) d = 0 $$ or $$\Delta v - d\,\Delta \omega = -v_A$$ | {
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string-theory, conformal-field-theory
is
$$
\mathcal{F}_{\Delta_s}^{(s)} = \cdots + \frac{\langle V_1V_2 L_{-n}|\Delta_s\rangle \langle V_3V_4L_{-n}|\Delta_s\rangle}{||L_{-n}|\Delta_s\rangle ||^2} + \cdots
$$
In this contribution the 3pt functions that appear in the numerator are $c$-independent. So if the denominator becomes infinite, the contribution vanishes. | {
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electromagnetism, electric-fields
Lorentz Transformation of Electric and Magnetic Fields | {
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angular-momentum
Title: Addition of angular momentum - normalization issue? If we have the raising and lowering operators for separate particles $J_1^\pm$ and $J_2^\pm$, we may define the total angular momentum operator $J$ and the corresponding raising and lowering operators as $J^\pm = J_1^\pm + J_1^\pm$. The intuition is difficult for me here since the left side lowers the z component of spin by one unit while the right side seems to do so by two units.
Now, say this acts on the two spin half particles in the state $\vert{\uparrow\uparrow}\rangle$. To preserve the norm, I need to have a factor of $\frac{1}{\sqrt 2}$ somewhere since I should get the state $\frac{1}{\sqrt 2} (\vert{\uparrow\downarrow}\rangle + \vert{\downarrow\uparrow}\rangle)$.
Yet the definition of any addition of angular momentum operator simple adds the two corresponding operators without normalization e.g. $J_z = J^1_z + J^2_z$. What gives? $J_{\rm tot}^-$ only lowers the z component by 1 unit, not 2. | {
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octomap
Originally posted by mgruhler with karma: 12390 on 2015-09-10
This answer was ACCEPTED on the original site
Post score: 0
Original comments
Comment by ktiwari9 on 2015-09-10:
Hmm i see. Well i tried different max_range values from 5.0 all the way upto 24.0 but nothing seemed to change. The original grid values are still strange. | {
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homework-and-exercises, special-relativity, metric-tensor, coordinate-systems, observers
So I'm OK until the step $\frac{dt}{d\tau}= \frac{1}{\frac{d\tau}{dt}},$ but he derives $\frac{d\tau}{dt}=\sqrt{1-v^2}$ (where I assume $v$ is just the time derivative of $(x(t),y(t),z(t))$) using some shaky argument:
$$d\tau=\sqrt{dt^2-dx^2-dy^2-dz^2}$$
and the divides by $dt$.
What is this supposed to mean mathematically? My interpretation must be different from what he had in mind because if we simply differentiate $\tau(t)=\sqrt{t^2-x^2-y^2-z^2}$ by $t$, using the chain rule we get
$$\frac{d\tau}{dt}=\frac{t-xv_1-yv_2-zv_3}{\sqrt{t^2-x^2-y^2-z^2}}$$
Which is different from $\sqrt{1-v^2}$ as can be seen by the case when $v=0$ and $x$ is not.
If we interpret the $dt$-s as differential forms with $d\tau$ the derivative of $\tau$ defined on an open subset on the Minkowski space we get the same result and
$$d\tau=\sqrt{dt^2-dx^2-dy^2-dz^2}$$
simply does not hold. | {
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