text stringlengths 1 1.11k | source dict |
|---|---|
\\ 0& 1 & 0 &0 \\ 0 & 0 & 1 & 0\\ \end{bmatrix}$$. The roots of the linear equation matrix system are known as eigenvalues. It doesn’t shrink anything, it doesn’t expand, it doesn’t rotate or collapse or shear. By continuing you agree to the use of cookies. For any whole number n, there’s a corresponding Identity matrix, n x n. 2) By multiplying any matrix by the unit matrix, gives the matrix itself. If any matrix is multiplied with the identity matrix, the result will be given matrix. any vector is an eigenvector of A. For a square matrix A, an Eigenvector and Eigenvalue make this equation true:. If A is the identity matrix, every vector has Ax D x. In general, the way acts on is complicated, but there are certain cases where the action maps to the same vector, multiplied by a scalar factor.. Eigenvalues and eigenvectors have immense applications in the physical sciences, especially quantum mechanics, among other fields. Rearrange . Copyright © 2020 Elsevier B.V. or its licensors or | {
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"url": "http://waynerogersltd.co.uk/blog/y90gfw.php?tag=2c219c-twitter-status"
} |
algorithms, time-complexity, algorithm-analysis, optimization, operating-systems
Title: Combining fork() and algorithms Today in my algorithms class, my professor explained how in divide and conquer algorithms we do things in "parallel" although I felt it was not exactly in parallel. Then I remembered from OS the fork() system call that creates literally another child process and computes in parallel with the parent process. Can we combine these two to give an algorithm that betters the usual Time complexity?
Although I just realized we have to wait for the child process to complete before the parent, still, some amount of computation can be done in parallel or is there something I am missing?
PS: I am new to this platform so sorry if this isn't the type of questions to be asked here
Can we combine these two to give an algorithm that betters the usual Time complexity? | {
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arc, if the perimeter of sector a! In metric units or imperial units substituting the above given data in the previous function ; (.! Is enclosed between its two radii and an arc is called a sector a circle and angle of radians!, or the distance around the outside edge, can be a tricky. Before I 'd fully read the question part of a circle of sectors equation. Knowledge: Rounding with significant figures and decimals videos, worksheets, 5-a-day and much more area of circle. Whose perimeter of a sector is r+θr+r units to be in metric units or imperial.! Portion of the arc L+2r units calculating the area and perimeter of the by. If the angle subtended at the center of the sector is a cm perimeter of sector units 42 /180+2 25... Significant figures and decimals, so the the area and perimeter of a circle containing a of! Examples to explain what a sector of a sector a region bounded by radii... 8 worksheets found for - perimeter of the sector is a region bounded by arc... Disucussed on | {
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Characteristics Computationally independent: each element computed in the result matrix C, c ij, is, in principle, independent of all the other elements. 6 Another Recursive Algorithm 4. Provide your analysis for the following problem statement: Write a program that will calculate the results for the multiplication table up to 10x10 in steps of 1 beginning at 1. cient implementation of sparse matrix multiplication on a memory intensive associative processor (AP), verified by extensive AP simulation using a large collection of sparse matrices [41]. We then "combine" the middle row of the key matrix with the column vector to get the middle element of the resulting column vector. The multiplier contains only 0s and 1s,. The algorithms classes I teach at Illinois have two significant prerequisites: a course on discrete mathematics and a course on fundamental data structures. Block matrices are briefly discussed using 2 × 2 block matrices. I have a question for you about your approach. What | {
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ds.data-structures, analysis-of-algorithms
("Analysis" in general is even more widely useful, but since your Q is specifically about a Real Analysis class I will stick to that. Just some mentions: differential equations can be used to derive phase transitions in combinatorial settings such as random graphs, SAT algorithms, clique algorithms, etc. Complex analysis can be used to estimate growth rates as in the generating function approach to bounding recurrence relations in algorithms. And it shows up a lot in things like the Unique Games Conjecture, hardness of approximation, and metric embedding.) | {
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java, thread-safety
The server uses this interface:
import java.util.Collection;
import javax.ejb.Local;
@Local
public interface GeneratorCancelledLocal {
public void setJobs(final Collection<String> jobs);
}
And here's the implementation:
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import javax.ejb.Stateless;
@Stateless
public class GeneratorCancelled implements GeneratorCancelledLocal, GeneratorCancelledRemote {
private Collection<String> jobs;
public void setJobs(final Collection<String> jobs) {
this.jobs = Collections.synchronizedSet(new HashSet<String>());
this.jobs.addAll(jobs);
}
@Override
public boolean isJobCancelled(final String jobId) {
return jobs != null && jobs.contains(jobId);
}
} | {
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"url": null
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condensed-matter, resource-recommendations, elements, data
Title: Pseudo-potential form factors for gold Can anyone suggest a reference in which I can find the Fourier coefficients of the pseudopotential of gold?
I cannot find them anywhere in literature.
I need them to compute the role of plasmon decay in the production of secondary electrons in gold as suggested in this paper for aluminum. As far as I can understand, the pseudopotential should be used in connection with the nearly free electron (NFE) approximation.
A preliminar warning is that, while NFE approximation works well with the alkali metals and reasonably well with most of the s-p bonded metallic systems, application to $d-$electrons metals somewhat transcends the reasonable limits of applicability of the theory.
Nevertheless, in the 70's a lot of work have been done to derive good quality pseudopotentials that could be used in connection with NFE theory. | {
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beginner, io, go
"github.com/BurntSushi/toml"
)
func main() {
var config client.Configuration
_, err := toml.DecodeFile("config.toml", &config)
if err != nil {
log.Fatal(err)
}
var wg sync.WaitGroup
wg.Add(1) //<- Extra points if you can tell me how to handle
//my goroutines. All are never ending for loops
record := make(chan string)
for id, camera := range config.Cameras {
h264 := make(chan client.Frame)
num := fmt.Sprintf("%v", id)
stream := "stream" + num
fromClientPort := ":808" + num
err = syscall.Mkfifo(stream, 0775)
if err != nil {
log.Println(err)
}
pipe, err := os.OpenFile(stream, os.O_RDWR, os.ModeNamedPipe)
if err != nil {
log.Fatal(err)
}
w := bufio.NewWriter(pipe)
conn, err := auth.Login(camera.Address, camera.Password, fromClientPort, camera.Retries)
if err != nil {
log.Println(err)
continue
}
defer conn.Close()
go client.Read(conn, h264)
go client.Write(w, h264, record) | {
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ros, navigation, costmap, collision-map
[ WARN] [1411756064.480653208]: Failed to add frames to existing band
[ WARN] [1411756064.824642032]: Map update loop missed its desired rate of 5.0000Hz... the loop actually took 0.2956 seconds
[ WARN] [1411756064.880660273]: Calculation of Distance between bubble and nearest obstacle failed. Frame 105 of 130 in collision. Plan invalid
[ WARN] [1411756064.880743612]: Conversion from plan to elastic band failed. Plan probably not collision free. Plan not set for optimization
[ERROR] [1411756064.880786228]: Setting plan to Elastic Band method failed!
[ERROR] [1411756064.880828885]: Failed to pass global plan to the controller, aborting.
[ WARN] [1411756064.480605628]: Calculation of Distance between bubble and nearest obstacle failed. Frame 0 of 5 in collision. Plan invalid
[ WARN] [1411756064.480653208]: Failed to add frames to existing band | {
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newtonian-mechanics, projectile, drag, coriolis-effect
Gravity should not be included in the coriolis equations. Assuming that your $g$ is the observed free-fall acceleration (gravity force + centrifugal), that your object has the same cross-sectional area and drag coefficients in all three x,y,z directions (and $v_x$ in equation 3 should be $v_z$), then you can use Newton's Law $\ddot{\vec{r}} = \vec{g} + \text{ coriolis } + \vec{F}_{drag}/M$ for each coordinate (let $\gamma = C_d \rho A/(2M)$) to get your equations of motion:
$$\ddot{x} = 2 \Omega v_y \sin(\phi) - \gamma |v| v_x$$
$$\ddot{y} = -2 \Omega (v_z \cos(\phi) + v_x \sin(\phi)) - \gamma |v| v_y$$
$$\ddot{z} = 2 \Omega v_y \cos(\phi) - g - \gamma |v| v_z$$ | {
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performance, php, mysql, mysqli
Generally it is best perform as few database queries as are necessary. If there were queries executed inside of a loop where data was selected based on a filter condition, it may make sense to perform one query and filter the data inside of the loop. But in this case, there are simply two similar but unique queries.
You didn't include the implementation for $db_handle->runSelectQuery() but the implementation might affect the answer as well. If that method uses a function to get all results at once (e.g. mysqli_fetch_all()) then it might be better for performance, but otherwise if it fetches results one at a time (e.g. using mysqli_fetch_all() until NULL is returned) then that might add a lot of overhead with looping over results in that method and then your code looping over the results for display purposes.
So in order to get a better answer, you must experiment with your data.
if so how to merge ? | {
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Another solution that's more mechanical and generalizable to other arrangements like two pair or full house:
We know we must have a 4-3-3-3 hand. You can pick any card for the first suit: 52. The next three cards must match the suit of the first so there are 12 x 11 x 10 possibilities for those. Now for the 4th card, we can pick any card not in the 1st suit: 39. Using the same reasoning as before, for the next two cards there are 12 x 11 possibilities. We continue until we have picked all cards:
$$X = (52 \times 12 \times 11 \times 10) \times (39 \times 12 \times 11) \times (26 \times 12 \times 11) \times (13 \times 12 \times 11)$$
$$X$$ gives us all arrangements of the pattern WWWW XXX YYY ZZZ, as such we overcount all the internal arrangements of W, X, Y, and Z ($$4!3!^3$$). We also overcount that X, Y, and Z can be interchanged ($$3!$$).
So the answer is $$X /(4!3!^4) / {52 \choose 13}$$. | {
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I suppose I will answer my own question since I think I've figured it out. It comes down to the fact that the functions $a_I$ and $b_J$ are technically 0-forms. Then we use algebraic properties of the wedge product and look at what those algebraic properties tell us when a 0-form is involved.
First, by the anticommutativity of $\wedge$, which says that for a $k$-form $f$ and an $\ell$-form $g$ $$f\wedge g=(-1)^{k\ell}g\wedge f.$$ So, for a 0-form $f$ and an $\ell$-form $g$, we get $f\wedge g=(-1)^{0\cdot \ell} g\wedge f=g\wedge f$.
Second, Tu remarks on page 37 that the wedge product of a 0-form $f$ and an $\ell$-form $\omega$ is actually regular multiplication; that is $f\wedge \omega=f\omega$. So, at a point $p$ we have $(f\wedge\omega)_p=f(p)\omega_p$. | {
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general-relativity, special-relativity, gravity, reference-frames, inertial-frames
Title: Does a gravitational field get transformed when switching from one inertial frame to another? We know that electric and magnetic fields get transformed when switching from one inertial frame to another as per the rules governed by special relativity. What about gravitational fields? In general relativity the term “gravitational field” is a little ambiguous. There are at least three quantities that could qualify. The one that is most central to GR is called the metric. The one that best describes the curvature aspect of GR is called the Riemann curvature tensor. The one that is closest to the Newtonian gravitational field is the Christoffel symbols.
In a very important sense, the metric and the curvature tensors do not change when switching from one reference frame to another. Just the components in the coordinate basis change, but the underlying geometric object is the same. | {
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general-relativity, metric-tensor, gravitational-waves, stress-energy-momentum-tensor, linearized-theory
\end{equation}
We can rearrange this equation as
\begin{equation}
\hat{\mathcal{E}^{(1)}} h^{(2)}_{\mu\nu} = T^{(\rm eff)}[h^{(1)}]_{\mu\nu}
\end{equation}
where $T^{\rm eff}[h^{(1)}]_{\mu\nu}$ is an effective stress-energy tensor that depends on the first order perturbation $h^{(1)}_{\mu\nu}$. Therefore, you can think of the stress-energy associated with gravitational waves as sourcing a higher order correction to the metric itself. This leads to some very interesting phenomena, such as non-linear gravitational memory. | {
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sage: 11*(-114) + 5*251
1
(3) We pass from the particular solution for $11X+251Y=1$ above to a particular solution for $11x+251y=61$. We compute $5\cdot 61=305$, and reduce modulo $11$ to get either $8$ or $-3$. For both we get then a solution...
sage: ( 61 - 251*8 )/11
-177
sage: ( 61 - 251*(-3) )/11
74
Here is the right point to mention that any other solution for the $x$-part differs from the above special one by a multiple of $251$.
(4) This solves the problem after the division with gcd $=3$, we can take $x=74$ modulo $251$. And also the initial problem, also taking $x=74$ modulo $753$.
I did not try to do a quick expedition of the human facts for the human solution, but even if... there would have been maybe the half of the line. This is somehow too much, compared with the following solutions of the same problem:
sage: R = Zmod(251)
sage: R(61)/R(11)
74
sage: R(11)^(-1) * R(61)
74
sage: R.is_field()
True | {
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javascript, html, css, matrix
function randomLetter() {
return characters.charAt(Math.floor(Math.random() * characters.length));
}
function generateLine(columns) {
var line = document.createElement('div');
while (columns--) {
var letter = document.createElement('span');
letter.style.color = randomGreen();
letter.innerHTML += randomLetter();
line.appendChild(letter);
}
return line;
}
function writeLines(container, lines, columns) {
for (var i = 0; i < lines; i++) {
container.appendChild(generateLine(columns));
}
} | {
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quantum-algorithms, resource-request, machine-learning, quantum-enhanced-machine-learning
Title: Introductory material for quantum machine learning In the past few days, I have been trying to collect material (mostly research papers) related to Quantum machine learning and its applications, for a summer project. Here are a few which I found interesting (from a superficial reading):
Unsupervised Machine Learning on a Hybrid Quantum Computer (J.S. Otterbach et al., 2017)
Quantum algorithms for supervised and unsupervised machine learning (Lloyd, Mohseni & Rebentrost, 2013)
A Machine Learning Framework to Forecast Wave Conditions (James, Zhang & O'Donncha 2017)
Quantum Neuron: an elementary building block for machine learning on quantum computers (Cao, Guerreschi & Aspuru-Guzik, 2017)
Quantum machine learning for quantum anomaly detection (Liu & Rebentrost, 2017) | {
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ros, threads
Original comments
Comment by Geaper on 2016-06-07:
Thx for helping. In tum_ardrone_gui.h I will post it.
Comment by Geaper on 2016-06-07:
Already posted it.
Comment by Pablo Iñigo Blasco on 2016-06-07:
you must not add code into any .h, only definitions.
Is the cpp code you showed part of the tum_ardrone_gui.h?
Comment by Geaper on 2016-06-07:
Everything works perfectly if I compile only one UINode. I just copy-pasted and renamed another folder to UINode2. But I cant compile UINode and UINode2 because it gives me the error above.
tum_ardrone_gui.h is the header file. It only declares functions
Comment by Pablo Iñigo Blasco on 2016-06-08:
It is hard to say what you have to say if we do not see the whole code and the cmake files and the contents of all the files you use. Anyhow what I can tell you is that your problem is a very typical linking problem in C++ project and it can essentially be solved through the guidelines I told you.
Comment by Geaper on 2016-06-08: | {
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javascript, jquery, game, rock-paper-scissors
If your colleagues are used to object oriented programming, this style might be more familiar.
Always use brackets
if ($input.val() === '-1') { return; }
I personally don't mind conditions within one line, but dropping the brackets is bad practice - and can lead to strange behaviours, especially in JavaScript.
Furthermore, I wonder why u used the dollar-sign at the beginning of the $input-variable?
Edit:
I share @Barts's opinion from the comments - it's not neccessary to use jQuery in this example. You should show them jQuery once they know the basic principles of JavaScript. | {
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c#, html, asp.net-mvc, razor
You should also get into the habit of using .Any() instead of Count() > 0 as Any will stop iterating after it finds the first item that matches the filtering (usually not a big deal, but the collection could get rather large, and it's a minor change to coding that could give big performance enhancements).
The only other thing I might recommend would be to have a CSS class for border-color:red instead of inline styling. | {
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scikit-learn, regression, activation-function
Is it possible to build a more customized network with MultiLayerPerceptron or perhaps from individual layers (sknn.mlp)?
UPDATE:
In the documentation for MultiLayerPerceptron it does say: | {
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material is doubled its... -- Create animated videos and animated presentations for free is that a range... Policy and cookie policy most sex and satisfaction, traditional couples had slightly less, and.. Toastmasters International he has systematically built his self-confidence and communicating ability in line with Larry Storeteling.... In one decreases and the other doubles too Year 10 take the of. One or more predictor variables and a response variable the effect that different training regimens have on player performance secure. Non-Countermonotonic dependence two variables where one variable, the other variable will not learn analyze. And circles, Problems, and often monotonic relationships, in essential,... Will also double ( example: for a non-linear relationship reflects that unit! Equation or physical system by looking at it promoted in Starfleet alternative to a linear equation forms a line! Two plots in this machine is: a guy is skating up a ramp 1.5m high 2m long | {
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ros-kinetic
I get the following error:
Loading node class: com.github.rosjava.rosjava_catkin_package_a.my_pub_sub_tutorial.Talker
Exception in thread "main" org.ros.exception.RosRuntimeException: Unable to locate node: com.github.rosjava.rosjava_catkin_package_a.my_pub_sub_tutorial.Talker
at org.ros.RosRun.main(RosRun.java:56)
Caused by: java.lang.ClassNotFoundException: com.github.rosjava.rosjava_catkin_package_a.my_pub_sub_tutorial.Talker
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.ros.internal.loader.CommandLineLoader.loadClass(CommandLineLoader.java:239)
at org.ros.RosRun.main(RosRun.java:54) | {
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not really sure how to approach this, im still thinking..
11. anonymous
Thanks so much for helping me, sir. But I must go to sleep now, its getting late for me. I will think about this tomorrow.
12. ganeshie8
Okay, have good sleep :) I'll try to post the solution over the night, pretty sure this is not that hard...
13. anonymous
thanks so much! i really appreciate it!
14. Loser66
|dw:1439562522979:dw|
15. Loser66
Consider vertex A. From AB, we have 7 triangles, and among them just ABF has center inside of it. That is the probability to get the center inside of the triangle is 1/7 for vertex A Same for others Hence the total is 1/7^9 but we have to subtract the overlap parts. I meant $$\triangle ABC$$ when consider node A will be overlap with $$\triangle BCA$$ for node B.
16. Loser66 | {
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electrostatics, voltage
Title: Electrostatic energy affected by dielectric medium
An isolated metallic object is charged in vacuum to a potential $V_0$ using a suitable source, it's electrostatic energy being $W_0$. It is then disconnected from the source and immersed in a large volume of dielectric with dielectric constant $K$. The electrostatic energy of the sphere in the dielectric is: | {
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GMAT Question of the Day - Daily to your Mailbox; hard ones only
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# M21-32
Author Message
TAGS:
### Hide Tags
Math Expert
Joined: 02 Sep 2009
Posts: 47983
### Show Tags
16 Sep 2014, 01:15
2
12
00:00
Difficulty:
95% (hard)
Question Stats:
54% (02:41) correct 46% (03:06) wrong based on 98 sessions
### HideShow timer Statistics | {
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"lm_q1_score": 0.9433475810629193,
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machine-learning, data-mining, statistics
min $\sum_{j=1}^m(\sum_{i=1}^nx_{ij}f(i)-\mu)^2$
Under the following constraints:
$\sum_{j=1}^mx_{ij}=1$ for all $i\in \{1..n\}$ to ensure exactly one assignment per sample
$x_{ij} \in \{0, 1\}$ to turn it into binary decision varibales
Depending on the size of your dataset and the solver you use this can be a heavy optimization, but there are a lot of greedy heuristics that will get you close fairly fast. | {
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# Recreational math: If $f(f(x))=e^x$, bound the integral $\int_0^1 f(x)dx$
I've been studying functions $f:\mathbb R\to\mathbb R$ that satisfy $f(f(x))=e^x$ (or, half-iterates of the exponential function). I know that there's only one such analytic function, but it's really hard to study since it is almost certainly non-elementary and I only know how to find finitely many terms of its Maclaurin Series.
Instead, I'm studying all continuous and increasing functions $f$ satisfying $f(f(x))=e^x$, and I've alighted on the following problem (which I came up with out of curiosity). I propose this question to all interested residents of MSE:
Given that $f$ is continuous and increasing and $f(f(x))=e^x$, find some bounds for the integral $$\int_0^1 f(x)dx$$
I've managed to come up with some pretty sweet bounds (in fact, they are the best possible bounds), and I'll post them after this question gets some answers.
I'll accept whatever answer has the tightest bounds, with a proof. | {
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clojure, canvas, clojurescript
That allows you to shorten the first line by a bit, and eliminate the do.
I tried reducing the 2 loops down into a function, but for it to be sane, I had to push a lot of the computation outside the function, which itself became very messy. An easy way to neaten it up though is to create an alias for .round js/Math. It can even be a macro so there's no runtime cost:
(defmacro roundM [expr]
`(.round js/Math ^double ~expr))
(doseq [x (range (roundM (/ (q/width) grid-size)))]
(q/line (+ grid-offset-x-mod (* x grid-size)) 0 (+ grid-offset-x-mod (* x grid-size)) (q/height))
(draw-number :horiz x grid-offset-x grid-offset-y))
and if ceiling instead of rounding is acceptable, you can drop the rounding altogether:
(doseq [x (range (/ (q/width) grid-size)))]
...) | {
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c++, performance, graphics, opengl
Title: OpenGL: Rendering the same sprite several times I've been trying to make refactor really simple 2d sprite engine in OpenGL. As a start, I'm trying to use instanced rendering to render several copies of the same sprite in a square formation across my screen. The code works fine but it is quite slow; I am getting about 20 frames a second when rendering 25600 copies. Really would apppreciate any insight into how to improve it.
main.cpp:
int instances = 25600;
float* data = new float[instances*sprite.getFloats()]; //sprite.getFloats just returns how much data each sprite pushes to the pipeline
while (!quit)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
for (int i = 0; i < instances; ++i)
{
sprite.loadData(data,SpriteParameter(glm::vec4(i%(screenWidth/dimen)*dimen,i/(screenWidth/dimen)*dimen,dimen,dimen)),i*sprite.getFloats()); //this part fills an array of floats with transfomration data
} | {
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electromagnetism, magnetic-fields, terminology, integration, vector-fields
EDIT: Then why are there gaps between the iron filing lines? Is it because of my previous statement | {
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homework-and-exercises, general-relativity, differential-geometry, curvature
Title: Confusion regarding Ricci Scalar Source: Thomas Moore's A General Relativity Workbook
Equation 1: $R= g^{\mu\nu}R_{\mu\nu} = R^\nu{}_\nu$
Equation 2: $R^{\mu\nu}=g^{\mu\beta}g^{\nu\sigma}R_\beta\sigma$
Question: Does $R$ also equal $g_{\mu\nu}R^{\mu\nu}$?
The Ricci Scalar $R$ is simply the trace of the Ricci Tensor $R^{\mu\nu}$ with respect to the metric $g_{\mu\nu}=g^{\mu\nu}$, so I don't see why the Curvature Scalar $R$ cannot be written as $g_{\mu\nu}R^{\mu\nu}$.
However, I am struggling to use Equation 2 to turn $R=g_{\mu\nu}R^{\mu\nu}=g_{\mu\nu}g^{\mu\beta}g^{\nu\sigma}R_\beta\sigma$ into Equation 1.
I was working on transforming $R^{\mu\nu}-(1/2)g^{\mu\nu}R+\Lambda g^{\mu\nu}=\kappa T^{\mu\nu}$ into $-R+\Lambda g^{\mu\nu}=\kappa T$, and I ran into this question. Using the equality $g_{\mu\nu}g^{\nu\sigma}=\delta_{\mu}^\sigma$ and the symmetry of the metric tensor, $g^{\sigma\beta}=g^{\beta\sigma}$, we have that
\begin{align} | {
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performance, r, automation
As you can see I mastered c/p and "search and replace" XD
But seriously, I'm wondering how I could "automate" these tasks. Maybe loading everything into a list and than write helper functions to apply certain actions (i.e. date formatting, selecting cols) to every list entry ?
I've always struggled to find good practice tasks, b/c during class I usually don't have the time to read up on nicer ways to make things work. So if anybody has some suggestions on where to find exercises on data analysis tasks, I would very much appreciate that.
Looking forward to read your replies !
Leon You can do more conversion as you read the data. The magic is done by the colClasses parameter to read.delim(). That parameter allows you to (1) convert the DateTime whilst reading and (2) drop unwanted columns.
Now I don't know what your data looks like, but here's a rough outline of how to read a datetime (untested). Note that you can do the + years(98) within the data-parsing class as well.
library(methods) | {
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cell-biology, physiology, zoology, pathology
human populations reveal that circulating auto antibodies directed
against the islets typically appear in the first 5 years of life, and
may be present for many years (sometimes 20 years or more) before the
disease develops. A similar latent period is seen with coeliac
disease, and implies that some sort of regulatory balance has been
achieved within the immune system, and subsequently lost. This opens
the door to the possibility of 're-education' of the immune system by
various forms of immune intervention.
Reference
The pathogenesis of Diabetes mellitus type 1 shows a strong tendency towards genetic related factors,
Reference | {
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c++, c++11, pointers
//non instatiable outside the header
base() {}
base(T * obj) : obj(obj) {}
virtual void operator = (T * obj) { this->obj = obj; } | {
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ros
Title: Explanation of Resolving paragraph 1.1.2 of Wiki "Names"
Hi to everyone,
I am new of ROS and I am trying to go through all the ROS tutorials. I ended up in this page:
http://wiki.ros.org/Names#Graph
and I didn't understand how to interpret the resolving paragraph 1.1.2 'RESOLVING'.
Could you please explain it to me in a better way?
thanks a lot,
Fab.
Originally posted by fabbro on ROS Answers with karma: 115 on 2014-10-03
Post score: 1 | {
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Outline: Proposition: P ,Q. Sort by: Top Voted. So P if and only if Q resolves into P > Q and Q > P, which is to say that . It is not to be confused with. The biconditional p q represents "p if and only if q," where p is a hypothesis and q is a conclusion. Its invention is often credited to Paul Halmos, who wrote "I invented 'iff,' for 'if and only if'—but I could never believe I was really its first inventor."[15]. In logic, a biconditional is a compound statement formed by combining two conditionals under “and.” Biconditionals are true when both statements (facts) have the exact same truth value.. A biconditional is read as “[some fact] if and only if [another fact]” and is true when the truth values of both facts are exactly the same — BOTH TRUE or BOTH FALSE. Ex : "parce que", "depuis que" I'll help you, if and only if, you promise to do your part. Used as a biconditional statement only conditional statement an associated letter or number now. To any conditional statement is one | {
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java, sql-server
/**
* Builds the required connection URL required by DriverManager.
* @param credentials ConnectionCredentials object containing the required configuration to connect to the database server instance.
* @return the connection URL built from the credentials
*/
private String getConnectionUrl(ConnectionCredentials credentials) {
String serverName = credentials.getServerName();
String databaseName = credentials.getDatabaseName();
String username = credentials.getUsername();
connectionUrl = String.format(
"jdbc:sqlserver://%s;databaseName=%s;",
serverName,
databaseName
);
return connectionUrl;
} | {
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image-processing, computer-vision
Gradient of isotropically low-pass filtered image
First, let's calculate a local gradient vector at each pixel for the green color channel in the full size sample image.
I derived horizontal and vertical differentiation kernels by differentiating the continuous-space impulse response of an ideal low-pass filter with a flat circular frequency response that removes the effect of the choice of image axes by ensuring that there is no different level of detail diagonally compared to horizontally or vertically, by sampling the resulting function, and by applying a rotated cosine window:
$$\begin{gather}h_x[x, y] = \begin{cases}0&\text{if }x = y = 0,\\-\displaystyle\frac{\omega_c^2\,x\,J_2\left(\omega_c\sqrt{x^2 + y^2}\right)}{2 \pi\,(x^2 + y^2)}&\text{otherwise,}\end{cases}\\
h_y[x, y] = \begin{cases}0&\text{if }x = y = 0,\\-\displaystyle\frac{\omega_c^2\,y\,J_2\left(\omega_c\sqrt{x^2 + y^2}\right)}{2 \pi\,(x^2 + y^2)}&\text{otherwise,}\end{cases}\end{gather}\tag{1}$$ | {
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Animate[Plot[nsol[x, t], {x, 0, 10}, PlotRange -> {0, 2}], {t, 0, 10}]
Update: For more information on how to model with the wave equation you can have a look at the (Finite Element Method) Acoustics in the Time Domain tutorial. This tutorial was added in V12.0 but the content presented should work in previous versions. The wave equation is one of the models presented there and many details about the equation and it's boundary conditions are presented. Hope this is useful. Search for Acoustics in the help system and the tutorial will come up.
This can be done with DSolve or DSolveValue.
WaveEquation = D[y[x, t], {x, 2}] - D[y[x, t], {t, 2}] == 0;
cond1 = Piecewise[{{1 - Abs[x - 1], Abs[x - 1] < 1}, {0, Abs[x - 1] > 1}}];
cond2 = Piecewise[{{1, 3 < x < 4}}, 0];
sol1 = DSolveValue[{WaveEquation, y[x, 0] == cond1,
Derivative[0, 1][y][x, 0] == cond2}, y, {x, 0, 10}, {t, 0, 10}]
Table[Plot[sol1[x, t], {x, 0, 10}, PlotRange -> All], {t, 0, 2}] | {
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python, beginner, game
def stop(): # ends the programm
global runner # shut it off
runner = False
os.system('cls')
print('goodbye')
# SPACESHIP CONTROL #
keyboard.add_hotkey('right', spaceship.move_right)
keyboard.add_hotkey('left', spaceship.move_left)
keyboard.add_hotkey('f', fire)
# GAME CONTROLS #
keyboard.add_hotkey('q', stop)
# MANAGER #
# starts manager and asteroid generator
manager = Thread(target=manager)
manager.start()
sleep(5) # you have to read instructions at the start
ast_generator = Thread(target=asteroid_generator)
ast_generator.start() # PARAMETERS #
score = 3 # initial lives
lenght = 10 # this for the arena
width = 10
The names you have given to these variables are bad. | {
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php, sql, mysql
</div>
</div>
<div class="row">
<div class="col-sm-2"><span class="graph-text">Meh</span></div>
<div class="col-sm-10 col-fixed-height">
<div class="matrix-inner" id="matrix<?php echo $item['id']; ?>-inner3" style="background-color:#7FC2D6"><?php if ($rating3 !== 0){ echo $rating3; } ?></div>
</div>
</div>
<div class="row">
<div class="col-sm-2"><span class="graph-text">Poor</span></div>
<div class="col-sm-10 col-fixed-height">
<div class="matrix-inner" id="matrix<?php echo $item['id']; ?>-inner2" style="background-color:#8CD2D2"><?php if ($rating2 !== 0){ echo $rating2; } ?></div>
</div>
</div>
<div class="row">
<div class="col-sm-2"><span class="graph-text">Bad</span></div>
<div class="col-sm-10 col-fixed-height"> | {
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fourier-series, approximation
I am not trying to predict future temperature or anything like that, I just need a function that can reproduce temperature oscillations with minimum period of ~12 hours. Your inclination to choose the largest magnitude coeffecients is the correct one. There is a Linear Algebra explanation for this having to do with orthogonaility.
However, your second question is more pertinent, I think. If your sole motivation for reducing the coefficient count is to reduce data entry effort then you are much better off formatting the output of your DFT analysis as syntax for inputting into your code. Then a simple copy and paste will do the job for you. You also greatly reduce your exposure to data entry errors. Depending on the volume, a custom programming solution which automates the copy and paste process might be economical.
Hope this helps.
Ced | {
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• It means that the Y under conditional sign (|) will hold constant while the Y above conditional sign (|) will be evaluated at all possible value? I thought that Y should be evaluated at both. For example, if Y takes value in $[1,2,3]$, we have:$\sum_y g(y).P(Y=y|Y=y) = g(1).P(Y=1|Y=1)+g(2).P(Y=2|Y=2)+g(3).P(Y=3|Y=3) = g(1)+g(2)+g(3) = \sum_y g(y)$ Apr 15 '21 at 5:59
• Yes to your question. You should only evaluate the part above the conditional sign. The part under the conditional sign is held constant. Apr 15 '21 at 6:16
• In this case, what is the different between $E[X|Y]$ and $E[X|Y=y]$? As my knowledge, The first term is rv and the second term is the value. Apr 15 '21 at 6:24
• Sometimes they are used interchangeably. I believe most texts on probability say that you should view $E[X | Y]$ as a random variable and you should view $E[X|Y=y]$ as a number that depends on $y$. Apr 15 '21 at 6:36 | {
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gazebo
Originally posted by agonzamart on Gazebo Answers with karma: 3 on 2013-06-21
Post score: 0
The <alwaysOn> should be a child of <sensor>, not <plugin>. This should force the sensor to be on all the time, and you should see a gztopic.
Originally posted by nkoenig with karma: 7676 on 2013-06-27
This answer was ACCEPTED on the original site
Post score: 0 | {
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# Question on star shaped domains
Let $X$ be a compact star shaped subset of $\mathbb{R}^n$ with center $x_0\in X$, that is, for every $x\in X$ the line segment $[x_0,x]=\{(1-t)x_0+tx : t\in [0,1]\}$ is contained in $X$.
Suppose $X$ has nonempty interior and that $\partial X$ is homeomorphic to $\mathbb{S}^{n-1}$.
My question is: does $X$ admit a center point in its interior?
I'm trying to generalize the statement "in $\mathbb{R}^n$, a compact convex set with nonempty interior is homeomorphic to the unit ball $\mathbb{D}^n$", which I proved using the fact that we can translate the convex so that the origin belongs to its interior and then the proof does not depend on any other point than the origin (that is a center for the convex).
Therefore, if the answer to my question is "yes", then it's true that "in $\mathbb{R}^n$, a compact star shaped set with nonempty interior and boundary homeomorphic to $\mathbb{S}^{n-1}$ is homeomorphic to $\mathbb{D}^n$. | {
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r
Here's one way you might go about this:
# create a presized data frame
Arows <- nrow(A.data)
Brows <- nrow(B.data)
correlation.result <- data.frame(t(matrix(c(0.0, 0.0, "foo"), nrow=3, ncol=Arows * Brows)), stringsAsFactors=FALSE)
colnames(correlation.result) <- c("rho", "p.val", "Gene") | {
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java, time-limit-exceeded, cryptography, hashcode
if hashset.contains(string(i)) break;
hashset.add(string(i));
}
print("This took " + i + " tried!") | {
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ros, rosaria, ros-indigo, aria
I don't know whether any conclusion was reached, but it seems like there are plans to host the (already GPL-ed) code on github.
Perhaps reaching out to that community if/when you keep having issues with downloading it would be a good first step?
The Internet Archive seems to have a large part of the mobilerobots site archived: archive.org/http://robots.mobilerobots.com/wiki/Main_Page.
Originally posted by gvdhoorn with karma: 86574 on 2018-05-02
This answer was ACCEPTED on the original site
Post score: 2
Original comments
Comment by chokapik on 2018-05-02:
Working perfectly thanks to you @gvdhoorn, I found both Aria and MobileSim in the Internet Archive.
I also came across a project on github https://github.com/amor-ros-pkg/libaria but the *.deb installation is just simpler. | {
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php, object-oriented
// We initialize the object and set the imageFilepath at the same time
$image = new Image("/home/jsanc623/Pictures/");
// We can get the image filepath
$imageFilepath = $image->getImageFilepath();
// We can get an array of all the files in a directory
$filesInFilePath = $image->getFilesInFilepath();
// We can then get the image titles for each image/
foreach($filesInFilePath as file){
$imageTitle[] = $image->getImageTitle($file);
}
print_r($imageTitle)
?> | {
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special-relativity, angular-momentum, field-theory, stress-energy-momentum-tensor, noethers-theorem
More concretely, we write $x^\mu \rightarrow x^\mu - \epsilon^\mu(x)$, so $\phi \rightarrow \phi + \epsilon^\mu \partial_\mu \phi$ and $\partial_\mu \phi \rightarrow \partial_\mu \phi + \epsilon^\nu \partial_\mu \partial_\nu \phi + \partial_\nu \phi \partial_\mu \epsilon^\nu$, leading to
\begin{eqnarray}
%
\delta \mathcal{L}
&=&
- \frac{1}{2} \left[ \eta^{\rho\sigma} + \lambda e^\rho e^\sigma \right] \left[ \delta(\partial_\rho \phi) \partial_\sigma \phi + \partial_\rho \phi \delta (\partial_\sigma \phi) \right] \\
%
&=&
- \frac{1}{2} \left[ \eta^{\rho\sigma} + \lambda e^\rho e^\sigma \right]
\left[ \epsilon^\nu \partial_\rho \partial_\nu \phi \partial_\sigma \phi
+ \epsilon^\nu \partial_\sigma \partial_\nu \phi \partial_\rho \phi
+ \partial_\rho \phi \partial_\nu \phi \partial_\sigma \epsilon^\nu
+ \partial_\sigma \phi \partial_\nu \phi \partial_\rho \epsilon^\nu \right] \\
%
&=&
- \frac{1}{2} \left[ \eta^{\rho\sigma} + \lambda e^\rho e^\sigma \right] | {
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# Evaluate $I_n = \int_0^{\pi / 2} \sin n \theta \cos \theta \,d\theta$ by integrating by parts twice
By integrating by parts twice, show that $$I_n$$, as defined below for integers $$n > 1$$, has the value shown.
$$I_n = \int_0^{\pi / 2} \sin n \theta \cos \theta \,d\theta = \frac{n-\sin(\frac{\pi n}{2})}{n^2 -1}$$
I can do this using the formula $$\sin A \cos B = \frac{1}{2}[\sin(A-B)+\sin(A+B)] ,$$ but when I try using integration by parts I get stuck in a loop of integrating the same thing over and over. | {
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ros, navigation, rospy, velocity, teleop
Title: Delay incoming messages
Is there a way in Rospy to delay incoming messages? Specifically, I wish to delay incoming velocity commands for teleop.
I can't use a sleep because I still need my program/node to run other processes.
I was wondering whether the queue size would have something to do with it?
Thanks!
Originally posted by piraka9011 on ROS Answers with karma: 32 on 2016-11-18
Post score: 1
According to http://wiki.ros.org/message_filters there is a TimeSequencer that does this, but only for C++ (and not much activity here about it, some example code is on http://stackoverflow.com/questions/34322075/ros-message-filterstimesequencer).
I tried this rospy.Timer based method and it looks like it is working, I don't know if it is robust- a bunch of Timers must be created behind the scenes and hopefully are taken care of properly:
#!/usr/bin/env python
import functools
import rospy
from std_msgs.msg import Float64
rospy.init_node("delay") | {
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bioinformatics, microbiology, theoretical-biology, cell-signaling, quorum-sensing
Title: Models of quorum sensing for multi-agent systems Quorum sensing is a system of stimulus and responses correlated to population density that is used by bacteria to coordinate gene-expression. I am looking for a simple computational/mathematical model of quorum sensing that abstracts away from the details of the mechanism implementing it inside the agent, but keeps the key inter-agent properties like diffusion rate, range, and timing.
Is there a standard abstract mathematical model of quorum sensing used by biologists?
I am not interested in the particulars of a specific organism, but would like a general model I could apply to capture the 'gist' for any organism that relies on quorum sensing for part of its behavior. | {
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c++, parsing, brainfuck
return 0;
} | {
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"tags": "c++, parsing, brainfuck",
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brain, neurophysiology, growth, regeneration
Studies have shown that neurogenesis folloing neuronal cell loss due to injuries occurs only within the germinal structures mentined above, and not in cortical or striatal structures. Even when neurogenesis in the striatum (but not cortex) has been reported following ischemic injury, the resulting neurons survive only a short time. Hence, under normal circumstances structural or functional recovery in non-neurogenic brain regions is limited (Hallbergson, 2003). | {
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ros
[rosmake-1] Finished <<< rgbdslam [FAIL] [ 17.08 seconds ]
[ rosmake ] Halting due to failure in package rgbdslam.
[ rosmake ] Waiting for other threads to complete.
[ rosmake ] Results:
[ rosmake ] Built 68 packages with 1 failures.
[ rosmake ] Summary output to directory
[ rosmake ] /home/wilk/.ros/rosmake/rosmake_output-20140127-004513 | {
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reinforcement-learning, sutton-barto, monte-carlo-methods, off-policy-methods, importance-sampling
So the behavioral policy does not take the bias into account. We want to evaluate the target policy which is closer to the optimal (optimal would mean always betting on $H$):
\begin{equation}
v(a|s_{\text{start}}) = \begin{cases}
0.9 & \text{for } a = \text{bet-on-H} \\
0.1 & \text{for } a = \text{bet-on-T} \\
\end{cases}
\end{equation}
First the analytical expected values for both policies without any importance sampling:
\begin{equation}
v_{b}(s_{\text{start}}) = 0.5 \cdot 0.6 \cdot 1 + 0.5 \cdot 0.4 \cdot 0 + 0.5 \cdot 0.4 \cdot 1 + 0.5 \cdot 0.6 \cdot 0 = 0.5 \\
v_{\pi}(s_{\text{start}}) = 0.9 \cdot 0.6 \cdot 1 + 0.9 \cdot 0.4 \cdot 0 + 0.1 \cdot 0.6 \cdot 0 + 0.1 \cdot 0.4 \cdot 1 = 0.58
\end{equation}
Now, let's consider importance sampling. Since our environment just has one relevant state the factors for importance sampling are
\begin{equation}
\rho_{t:T-1} = \rho = \frac{\pi(a | s_{\text{start}})}{b(a | s_{\text{start}})} = \begin{cases} | {
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evolution, speciation
Provided a significant advantage over their kin in the environment (which is likely, as being able to digest milk in an agrarian society opens up a new source of energy)...
or
Didn't hinder the child's ability to grow and produce fertile offspring of their own... | {
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Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why? | {
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semiclassical
Title: Beyond WKB approximation for energies In the first term the energies are given by the Wentzel–Kramers–Brillouin (WKB) formula
$$ \oint p dq = 2\pi \left( n+\frac{1}{2} \right) $$
However, can this formula be improved to include further corrections? For example the wave function in the WKB approach can be evaluated to several orders of magnitude in $ \hbar $ In the following, I'll describe to you how in principle one can compute higher order corrections to the Bohr-Sommerfeld condition.
In order to find higher order corrections to the Bohr-Sommerfeld formula, we need to include higher order corrections of the wavefunction of the form:
$$
\Psi(x) = \sum_n \hbar^n a_n(x) \exp\left(\frac{i}{\hbar} \int^x \sqrt{2m(E-V(y)) }dy\right)\,.
$$
Inserting in the Schrodinger equation and requiring fullfilment to each
order of $\hbar$, we obtain:
$$
a_0 = \frac{const.}{(2m(E-V(y)))^{\frac{1}{4}} }
$$
and
$$
a_k \Delta S + 2 \nabla a_k\cdot \nabla S = i \Delta a_{k-1}\,,
$$
where | {
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# Number of ways of reaching a point from origin [duplicate]
If we have a point p(x,y) in coordinate system [x>=0, y>=0; i.e 1st quadrant]
How to find the number of ways of reaching the point from origin (0,0).
Ex: If p(2,1);
way1: 0,0 -> 1,0 -> 2,0 -> 2,1
way2: 0,0 -> 1,0 -> 1,1 -> 2,1
way3: 0,0 -> 0,1 -> 1,1 -> 2,1
Is it possible to have a mathematical equation for it? and How? if we don't have, what's the best possible way to find those.
Rules:
1. You can move only in horizontal, vertical directions (diagonal is not possible)
2. you can only move to the point (a,b) such that 0<=a<=x and 0<=b<=y
3. a, b can be only natural numbers
-
## marked as duplicate by JavaMan, Fabian, Srivatsan, Martin Sleziak, Asaf KaragilaJan 29 '12 at 11:44 | {
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navigation, ekf, gps, navsat-transform, robot-localization
I've documented the various errors as best I can below. Any help or advice will be greatly appreciated.
UPDATE 1:
I can finally edit this again when I couldn't for a few days?! Anyway...
Here are my updated ekf_launch files: ekf_and_gps_localisation.launch
And separate launch files for each node: ekf_local.launch, ekf_global.launch, navsat_transform.launch | {
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newtonian-mechanics, rotational-dynamics, reference-frames
When a pivot point other than the center of mass is accelerating, then you need torque around the pivot point just to keep the object's center of mass aligned with the pivot.
The angular velocity and angular acceleration of the object are the same around any parallel axis in an inertial frame of reference. Net torque and rotational inertia change when that pivot axis changes, but the rotational effect is the same. When the pivot axis accelerates, the frame of reference around the pivot axis is no longer inertial. You need an artificial effect to compensate for this, just as centrifugal acceleration must be added to a rotating reference frame to make Newton's Laws valid in that non-inertial frame. | {
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the graph is one which is to! Ll present a general formula to calculate the maximum number of Regions ( r ) = –! That the vertices in the graph contain maximum of edges is limited and a user can specify directions... Re considering a standard directed graph Answer: 25: Confused About the Answer is.... – v + 2 = 20 end up with a quadrilateral to our,... The maximum number of isolated vertices maximally connected as the only vertex cut disconnects! Important DSA concepts with the formula and Answers vertices should not have any edges this! Maximize the number of isolated vertices of the vertices can belong to most... Independent directed edges then a cut edge is specified by its two and. 30 – 12 + 2 = 20 such that the vertices, called the adjacency.! Endpoints and order does n't matter assuming that the vertices are reachable from one another endpoints order... Please use ide.geeksforgeeks.org, generate link and share the link here maximum number of edges in a graph with n vertices by ’! | {
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"url": "http://tarasytynieckie.com.pl/halo-ce-kzhjd/038528-maximum-number-of-edges-in-a-graph-with-n-vertices"
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parallel-computing
Title: Desirable fraction of non-parallelizable code in Amdahl's law I read that if $\alpha$ is the fraction of the code that cannot be made parallel then it is desirable that $\alpha < \frac 1 p$ where $p$ is the number of processors.
Why is it the case?
The speed-up is $S(p) = \frac{T_1}{T_p} = \frac{p}{1+(p-1)\alpha}$ When $\alpha=\dfrac1p$, the speedup is $$\dfrac{p^2}{2p-1}\sim50\%\,p$$ so the processors are well utilized. | {
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thermodynamics, energy-conservation, work, reversibility
The essential point to note is that the end points of the reversible and irreversible processes must be the same to discuss the question under consideration. With this proviso, we see that ΔU= W for a reversible adiabatic process and ΔU ≠ W' for an irreversible adiabatic process. | {
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"tags": "thermodynamics, energy-conservation, work, reversibility",
"url": null
} |
inorganic-chemistry
And secondly, it is sp2 hybridized at the nitrogen atom. Thus, when you join the two NO2 molecules together, taking the relative orientation of the sp2 orbitals and how they should overlap to form a sigma bond in mind, you can see why N2O4 is planar. Because the N=O bonds (I write the "=" symbol for double bond for simplicity, it should be about 1.5 order due to resonance) heavily repulse each other when they are in the planar position, it weakens the N-N bond. Indeed this bond is so weak that it is homolytically dissociated at near below room temperature or above, creating basis for the popular equilibria between NO2 and N2O4. | {
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search-algorithms, heuristics
Title: How do I solve a search problem on an infinite graph? I have a search problem that requires me to find a path from $v_s$ to $v_g$ in the graph $G = (V, E)$ where $v_s, v_g \in V$ are the start and goal vertices in a set of vertices and $E \subset V \times V$ is an undirected set of edges connecting vertices. Both $V$ and $E$ can be infinite. Each edge has an associated cost $c: E \rightarrow \mathbb{R}$ and the cost of a path (an ordered set of edges) between adjacent vertices that leads from the start to the goal is the sum of the cost of all of its edges. My goal is to find the path with minimal cost (assume it exists). | {
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and at 0 when it's 90 degrees on either side and at the bottom. A pendulum bob is released from some initial height such that the speed of the bob at the bottom of the swing is 1. b) Find the new period of the pendulum. The actual plane of swing appears to rotate relative to. Right at the middle point, when the pendulum is momentarily moving at a constant speed, the acceleration is purely in the radial direction, as it should be for an object in circular motion at a constant speed. Acceleration in SHM The rate of change of velocity is the acceleration of the vibrating particle. All the forces are 400 N to the left and 300 N to the right, so the net force is -400+300=-100 N to the left. segment or arm AB of mass M 1 and An equal and opposite reaction force is exerted at the hinge joint if there is no acceleration of the rod did the lower segment come to a stop at the bottom of its swing, as it apparently did in trial 3 of Ref. At the bottom-most point, both the centrifugal force and the | {
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gravity, string-theory, gauss-law, spacetime-dimensions, compactification
String and Superstring theory (really, M-theory, see
http://en.wikipedia.org/wiki/M-theory, and
http://en.wikipedia.org/wiki/String_theory#Extra_dimensions), require
a minimum of 9 spatial dimensions. If those, or some of those are big
dimensions, then the weakness of gravity might be explained, and then
if we then look at smaller and smaller distances, gravity is
(relatively) stronger. It is also one reason there are attempts to
measure the strength of gravity at smaller and smaller distances -- to
see if it does not go as $1/r^2$. So far, as I said above, it's only
been down to about 1 millimeter, and nothing strange has been found.
String Theory mostly has it (because the strings that cause gravity
were thought to be able to extend in all dimensions, whereas normal
forces like nuclear and electromagnetism strings are constrained to
move in our 3D brane) that gravity propagates in the 10 spatial | {
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simulation, real-time
How does this apply to your situation?
Initially, the priority queue contains event A at time 11:00:00 and event B at time 11:00:01.
You pop off the earliest item in the priority queue. This is event A at time 11:00:00. So, at virtual time 11:00:00, you simulate event A and discover that it will make a call to the server. Presumably this involves sending a message to the server, which will arrive at the server at time 11:00:02. So, you add an event (let's call it event C) to the priority queue, with time 11:00:02, indicating that at that time, the server will receive a message telling it to determine what event to do next.
Now the priority queue contains event B at time 11:00:01 and event C at time 11:00:02. | {
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beginner, haskell, file
Title: File manipulation with Haskell I am trying to pick up Haskell!
But I feel like my code is a bit painful to write and read.
Do you have any pointers on how to improve its readability / style?
main = do
contents <- fmap tail . fmap lines . readFile $ "testInput"
let input = map pair_to_tuple .(map (map read)) . map words $ contents :: [(Int,Int)]
let result = map (uncurry waffles) $ input
let decorated_result = ["Case #" ++ show i ++ ": " ++ show s | (i,s) <- zip [1..length result] result]
writeFile "output.txt" $ unlines $ decorated_result
waffles row col = (row - 1)*(col - 1)
pair_to_tuple [a,b] = (a,b)
This script reads a file whose first line is a title, then every line is a couple of numbers. Then it drops the first line, and processes every pair of numbers using the function waffles, then it writes it back to an output file. contents <- fmap tail . fmap lines . readFile $ "testInput" | {
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complexity-theory, reductions
Title: Are Path-systems P-complete under logspace many-one reductions? As far as I know, the admissability of a path-system is an example of a P-complete problem.
However, I am not sure under which kind of reductions (many-one or turing-reductions? logspace or AC$^0$ reductions ... ?).
Can anyone explain me under which reductions are Path-systems P-complete, please? Admissible path-systems are, indeed, P-complete under many-one logspace reductions.
On the paper [1] we can see that Cook, given a Turing Machine $M$ that runs in $T(n)$ and some input $w$, builds a path-system problem that is admissible iff $M$ accepts $w$. Hence, the reduction is many-one.
The reduction is logspace, as already claimed by Cook, since it uses log(T(n)) memory, and hence, it uses k*log(n) memory if T(n) is $n^k$.
[1] Cook, Stephen A. "An observation on time-storage trade off." Proceedings of the fifth annual ACM symposium on Theory of computing. 1973. | {
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telescope, amateur-observing, optics, telescope-making
If so, you might have to invest in an achromatic objective to get rid of this problem, or look only at things that are monochromatic (and in Astronomy there aren't many of those!)
In addition to making sure the eyepiece lens is centered on the objective lens' axis, you also have to make sure the eyepiece lens isn't tilted. Both of those will cause problems and the point-like LED spot will show this. It might look like a fuzzy comet coma aberration. | {
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c#, beginner, number-guessing-game
if (player == 1 || player == 2)
{
if (player == 1)
return true;
else
return false;
}
} while (true);
}
public bool PlayAgain()
{
string resp;
Console.WriteLine("Would you like to play again?");
do
{
Console.WriteLine("(y / n):");
resp = Console.ReadLine().ToUpper();
}
while (!(resp == "Y" || resp == "N"));
if (resp == "Y")
return true;
else
return false;
}
private int GetHumanInput()
{
int guess = 0;
do
{
Console.WriteLine($"Guess a number between {_lbound} and {_ubound}");
Console.WriteLine("Enter your guess: ");
int.TryParse(Console.ReadLine(), out guess);
} while (guess == 0);
return guess;
} | {
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thermodynamics, drag, reversibility
For a reversible change, all these difficulties go away. The pressure and temperature of the gas are uniform throughout and viscous stresses are negligible, so the boundary pressure $P_B$ is equal to the average gas pressure, and the equation of state can be used to describe the pressure, volume, and temperature.
So, what do we do in the case of an irreversible change. Basically, for both irreversible and reversible changes, the equation for the work is the same:$$W=\int P_B\rm\; dV\;.$$ This is just the integral of the force the gas exerts on its surroundings over the distance the force is applied. But, unlike a reversible change, we can not depend on the equation of state to control the value of the boundary pressure $P_B$. So we need to control it manually from the outside, using either a pressure transducer at the boundary combined with a feedback control system on the piston movement, or, in simpler cases, by adding or removing a weight to the piston. | {
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inorganic-chemistry, metal
Try vacuum thermal deposition of a micron or so thickness of the Parylene family on the newly fabricated and cleaned metal - intrinsic, especially C, or F. Parylene polymer surface coats survive the insides of excimer lasers, protecting the excitation electrodes. If the lead still sticks, chemical cleaning should stop at the polyparylene film. Or not. Gotta test it. You are worried about vapor deposition not abrasion, so an inert barrier film is reasonable.
Google, parylene coating services
For aluminum or titanium vs. lead in chemistry, I'd pull one out of left field to try on test coupons: Rauchfuss' elixir: elemental sulfur dissolved in N-methylimdiazole (pyridine less so, very smelly, toxic, and don't get it on your skin or breathe the awful vapors). It goes through polysulfide-forming metals like a buzz saw, giving soluble products. I would expect aluminum to be inert; titanium is a toss-up. It should hit lead hard, probably. Test it small scale. | {
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in each case, there is a different relation of the field strength to the distance from the source of charge. The direction of the electric field at any point is radially outward from the origin if is positive, and inward (i. Draw an x axis along the rod. Although it is easy way to visualize the direction of the vector fields, electric field must be continuous lines as you know. Das 1 Centre of Advanced Study in Radiophysics and Electronics 1, Girish Vidyaratna Lane, University of Calcutta, Kolkata 700009, India E-mail: [email protected] Fieldduetoalineofcharge A generic guide to find electric field at a point by a line of uniform charge (straight, or circular) • General strategy: take an element dq of the charge and find electric field d E due to that element. The task requires work and it results in a change in energy. Where F is the electrostatic force between the source charge ‘q’ and the test charge ‘q 0 ‘. Since λ is the charge density of the line the charge contained within the | {
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period. An example of an ordinary annuity is a series of rent or lease payments. The present value calculation for an ordinary annuity is used to determine the total cost of an annuity if it were to be paid right now. An example of the future value of an annuity formula would be an individual who decides to save by depositing $1000 into an account per year for 5 years. The first deposit would occur at the end of the first year. If a deposit was made immediately, then the future value of annuity due formula would be used. Future Value of an Ordinary Annuity Example You have travel enthusiasm and curious to visit Asia but cannot afford the lump sum amount of$800. Currently, from your salary, you can save only $150 per month and you are searching for a source which would provide you the sum after 5 years to enjoy a trip to Asia. Present Value of Ordinary Annuity The ordinary annuity is an annuity, a stream of cash flows that occur after equal interval, in which each periodic cash flow | {
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contributing to it. Xcas is an interface to perform computer algebra, function graphs, interactive geometry (2-d and 3-d), spreadsheet and statistics, programing. object can have only values from the set of real numbers. For box1L, the complex numbers 1+2 i and 2+1 i are written as. We use the important constant e = 2. Python number method exp() returns returns exponential of x: e x. Complex number - how to find the angle between the imaginary axis and real axis? Ask Question Asked 5 years, 11 months ago. jp) http://dml. An introduction to matrix groups and their applications Andrew Baker [14/7/2000] Department of Mathematics, University of Glasgow, Glasgow G12 8QW, Scotland. 718 281 828 459. stackexchange. Complex numbers use I ; integer literals use Integer , float literals use Float , and repeating decimals use Rational. The NumPy libraries handles the mathematical functions. Complex Numbers¶ A complex number has a real part $x$ and a purely imaginary part $y$. To evaluate an | {
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c++, checksum
ebx, edi, ecx, eax are not good variable names, if you can give them more meaningful names, then do.
uint32 ecx = (hexform[i] + 1) * hexsum,
eax = ecx * hexform[i];
Personally, I think this is clearer:
uint32 ecx = (hexform[i] + 1) * hexsum;
uint32 eax = ecx * hexform[i];
The comment is really bad because it talks about hexform[i]^2 + hexform[i] * hexsum whereas ecx gets the value hexform[i] * hexsum + hexsum and eax gets the value hexform[i]^2 * hexsum + hexform[i] * hexsum. I think the comment needs a pair of parentheses if the code is doing what you meant.
To be robust, you should check whether the parse worked.
parseitemlink >> hex >> hexform[i];
You can trivially combine the first two for loops as well. | {
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Now, for general $f_n$, I can use $$\int_\Omega f_nd\mu = \sup\bigg\{\int_\Omega\psi_n d\mu:0\leq\psi_n\leq f_n, \psi_n: simple\bigg\}$$ Then \begin{split} \int_\Omega\sum_n f_nd\mu &= \sup\bigg\{\int_\Omega\sum_n\psi_n d\mu:0\leq\sum_n\psi_n\leq\sum_nf_n, \psi: simple\bigg\}\\ &=\sum_n\sup\bigg\{\int_\Omega\psi_n d\mu:0\leq\psi_n\leq f_n, \psi_n: simple\bigg\}\\ &=\sum_n\int_\Omega f_nd\mu \end{split} Can I do that? Won't I have the same problem with the non-convergence? Someone could help, please? | {
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by the context. In other words,. CS Subjects: Determinant of a matrix A is denoted by |A| or det(A). credit transfer. Determinant of a Identity matrix is 1. Let us try to answer this question without any outside knowledge. » Puzzles I We want to associate a number with a matrix that is zero if and only if the matrix is singular. The determinant of a square matrix is nonzero if and only if the matrix has a multiplicative inverse. We can use the above observation to quickly evaluate the determinant of an Identity Matrix as one. An identity matrix is a square matrix having 1s on the main diagonal, and 0s everywhere else. The theorem may be proven as follows. The determinant of a matrix A is denoted det(A) or det A or |A|. » Articles » Networks The determinant of a square matrix is nonzero if and only if the matrix has a multiplicative inverse. Sophia partners Thanks for the help. Run-length encoding (find/print frequency of letters in a string), Sort an array of 0's, 1's and 2's in linear | {
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algorithms, dynamic-programming, recurrence-relation, recursion
Initially, all dp[i][j] are false.
The base case is the empty string, dp[i][i] = true for all i.
The recurrence relation is, according to the observation above, dp[i][j] = true for i < j if s[i] == '(' and dp[i+1][j-1] == true and s[j-1] == ')' or there is an index k, such that both dp[i][k] == true and dp[k][j] == true. We can stipulate that i < k < j.
Here is the top-down version of the above approach, following the style in the question.
private static boolean topDown(String s, int i, int j, Boolean[][] dp) {
if (i > j) return false;
if (dp[i][j] != null) return dp[i][j];
if (i == j) {
dp[i][i] = true;
} else {
if (s.charAt(i) == '(' && s.charAt(j - 1) == ')' && topDown(s, i + 1, j - 1, dp)) {
dp[i][j] = true;
} else {
for (int k = i + 1; k < j; k++) {
if (topDown(s, i, k, dp) && topDown(s, k, j, dp)) {
dp[i][j] = true;
}
}
}
} | {
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python, programming-challenge, python-3.x, primes
Sometimes it seams that adding comments only masks unintuitive code (like putting lipstick on a pig). What would you suggest to improve the readability? Replace the list of all numbers up to n with a dictionary of primes only
As it stands, N holds mainly False values, which are never used. It would be more idiomatic to use a dictionary, plus Python's in operator, which tells you whether a particular key exists in the dictionary. As the proportion of primes below a given number n is approximated by \$n /\mathcal{ln}(n)\$, a dictionary containing only primes as keys would be smaller than your list by a factor of about \$n/\mathcal{log}(n)\$, while look-up would be just as fast.
Your prime sieve would look like this:
def prime_sieve(n):
'''Your docstring here.
'''
sieve = dict.fromkeys([i for i in range(n)]) # make a dict of all numbers up to n
for i in range(2, ceil(sqrt(n))):
if i in sieve:
for j in range(i**2, n, i): | {
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electromagnetism, magnetic-fields, electric-current
Title: Right Hand Rule Help: Part 1 I thought I understood the right hand rule but I guess not. Here is how I learned it in regards to finding the direction of the magnetic field vector of a current carrying wire. Point your thumb in the direction of the current and curl your fingers around the current-carrying wire. I’m guessing the palm points in the direction of the magnetic field. I have two questions about the following problem:
It seems like charge doesn’t matter in this problem. Why is that? | {
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neural-network, dataset, caffe
EDIT: I have made a blog post where I elaborate a little more. | {
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c#, .net
In the IncrementClientCountFor code the value is retrieved and then added to. If someone came in and updated the value the TryUpdate would fail as the count changed.
What should be used is the AddOrUpdate method. If the key doesn't exist it will be created and set to one. If it does exist it will call the update method. The update method could be called multiple times if the value changed before it could be set and will be set to the last good value.
public static void IncrementClientCountFor(string buildingName)
{
_buildingsSubscribedTo.AddOrUpdate(buildingName, 1, (s, i) => i++);
} | {
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general-relativity, coordinate-systems, metric-tensor
Title: Christoffel symbol for Schwarzschild metric I know that the christoffel (second kind) can be defined like this:
$$\Gamma^m_{ij} = \frac{1}{2} g^{mk}(\frac{\partial g_{ki}}{\partial U^j}+\frac{\partial g_{jk}}{\partial U^i}-\frac{\partial g_{ij}}{\partial U^k})$$
but I don't know how $U^i$ is defined (specifically for the Schwarzschild metric. The Schwarzschild metric is, in $-+++$ sign convention and units of $c = 1$ is
$$\mathrm{d}s^2 = -\left(1-\frac{2M}{r}\right)\mathrm{d}t^2 + \frac{\mathrm{d}r^2}{1-\frac{2M}{r}} + r^2\left(\mathrm{d}\theta^2 + \sin^2\theta\,\mathrm{d}\phi^2\right)\text{.}$$ | {
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homework-and-exercises, general-relativity, newtonian-gravity, orbital-motion, geodesics
With these conditions, we can perturb the metric linearly:
$$\begin{align}
g_{\mu \nu} &= \eta_{\mu \nu} + h_{\mu \nu} \\
g^{\mu \nu} &= \eta^{\mu \nu} - h^{\mu \nu}
\end{align}$$
where $\eta_{\nu \mu}$ is some canonical metric (Minkowski then in this case) and $|h_{\mu \nu}| \ll 1$ is a small perturbation.
If we then follow the time component our the geodesic equation:
$$\begin{align}
\frac{d^{2}x^{u}}{d\tau^{2}} + \Gamma^{\mu}_{\nu \lambda}\frac{dx^{\nu}}{d\tau}\frac{dx^{\lambda}}{d\tau} = 0
\end{align}$$
and then solve for time and spatial components (while taking the time derivative of a static field):
$$\begin{align}
\frac{d^{2}x^{\mu}}{d\tau^{2}} + \Gamma^{\mu}_{00} \left( \frac{dt}{d\tau} \right)^{2} &= 0 \\
\frac{d^{2}x^{\mu}}{d\tau^{2}} &= - \frac{1}{2} \eta^{\mu \lambda}\partial_{\lambda}h_{00} \left( \frac{dt}{d\tau} \right)^{2}
\end{align}$$
we see that when $\mu=0$:
$$\begin{align}
\frac{dt}{d\tau} = constant
\end{align}$$
and when we see that when $\mu=i$: | {
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molecular-biology, cell-biology, protein-expression
In the case of common cell lines, it's relatively easy to transfect/optimize the conditions to obtain abundant protein of interest for the study. | {
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thermodynamics
Title: Need some help proving the following statements in Thermodyamics? So in my second year thermodynamics class we are currently talking about entropy and deriving its definition from the 1st law.
$$\mathrm{d}q_{rev} = dU - dw_{rev}$$
$$= C_{V}(T)dT + PdV$$
$$= C_{V}(T)dT + \frac{nRT}{V}dV$$
And then it just says since the mixed second partial derivatives aren't equal, i.e.
$$(\frac{\delta Cv(T)}{\delta V})_T \neq (\frac{\delta(\frac{nRT}{V})}{\delta T})_V$$ dq is not an exact differential (no proof of this is given). It then stipulates by dividing both sides of the equation by T
$$\frac{\mathrm{d}q_{rev}}{T} = \frac{C_{V}(T)}{T}dT + \frac{nR}{V}dV$$
suddenly it becomes an exact differential because
$$(\frac{\delta Cv(T)/T}{\delta V})_T = (\frac{\delta(\frac{nR}{V})}{\delta T})_V$$ | {
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javascript, jquery
How can I improve this code, with regards to readability / maintenability first, performance then (not a lot of data, so not a big concern)? Instead of an array, and having to do a $.grep to check if the year is already in the array, consider using an object. That way, it's a key-value pair, and it's easier and faster to look up. You can convert the data to the final array later on.
Consider using promises instead of callbacks. It's much more flexible and allows better flow control than callbacks.
nameOfObject is misleading when all it is is just the year. Name it to year instead.
There's probably little sense breaking out that function unless something else uses it. It's better to inline operations in this case, making the code easier to trace.
Be wary of the use of new Date. Every time you do that, you create a date object. Since your timestamps are uniformly formatted, you might want to consider slicing off the first 4 characters and use it as year. | {
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Transpose of a Matrix and Eigenvalues and Related Questions, Eigenvalues of a Hermitian Matrix are Real Numbers, Eigenvalues of $2\times 2$ Symmetric Matrices are Real by Considering Characteristic Polynomials, Sequence Converges to the Largest Eigenvalue of a Matrix, There is at Least One Real Eigenvalue of an Odd Real Matrix, A Symmetric Positive Definite Matrix and An Inner Product on a Vector Space, True or False Problems of Vector Spaces and Linear Transformations, A Line is a Subspace if and only if its $y$-Intercept is Zero, Transpose of a matrix and eigenvalues and related questions. […], Your email address will not be published. Knowledge is your reward. Theorem C.6 The real symmetric matrix V is positive definite if and only if its eigenvalues Transposition of PTVP shows that this matrix is symmetric.Furthermore, if a aTPTVPa = bTVb, (C.15) with 6 = Pa, is larger than or equal to zero since V is positive semidefinite.This completes the proof. Here $${\displaystyle z^{\textsf | {
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} |
fft, radar
Given the FFT complexity as $2N\log_2(N)$ real additions and real multiplications where $N$ is the number of samples; the consideration would be if the complexity of the bandpass filter implementation needed (which could be efficiently mapped to a polyphase structure), would offset the savings in the FFT implementation, which could be further explored. In this example of reducing by a factor of 8, the number of real multiplications and real additions needed in the FFT is reduced by a factor of 48. The OP's case is just a factor of 2 resulting in a savings of 4 real multipliers and 4 adders...unlikely that we could win with other processing; but this does demonstrate at which point such options would be worth considering for sub-band processing. | {
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python, game, rock-paper-scissors
and the __lt__ method:
def __lt__(self, other):
return not self.__gt__(other)
is both redundant and incorrect (as pointed out in the comments, this is actually a less than or equal to that is written here, as any value that is not greater than will return true) and can be removed (the default version calls __gt__ and should handle your problem fine).
Finally for clarity I would define VERBS as a dictionary. It is more code, but it is also more readable:
VERBS = {"rock":"crushes", "paper":"covers", "scissors":"cut"}
this allows you to do the following in the main function:
verb = VERBS[player.sign]
and
verb = VERBS[computer.sign] | {
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general-relativity, black-holes, metric-tensor, causality, singularities
travels at 45 degrees. On the diagram of a black hole you can see that the event horizon is just the point where all light (and therefore everything) must hit the singularity because the singularity encompasses all of its possible future positions. | {
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discrete-signals
Discrete signals are mathematical objects and do not have to be physically realizable
Regarding the integration bounds: discrete signals don't need to have a finite support. There's nothing that states that discrete signals should be physically "realizable". Thus there is nothing wrong in defining, for example, the discrete signal $s(n) = \sin (2 \pi \frac{440}{48000} n)$. It has an infinite support and infinite energy. $s(n) = e^{-n^2}$ is another example of discrete signal with infinite support but this time finite energy. | {
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