text stringlengths 1 1.11k | source dict |
|---|---|
The CENTROID. Lesson Objectives: 1. To find the centroid, we find the midpoint of two sides in the coordinate plane and use the corresponding vertices to get equations. 911 GT3 New Center-of-Gravity Height and Variable Slalom Tests. Example: problem 9-18. RE: Center of Gravity of a surface March 22, 2013 12:03 PM (in response to Johnny Dupont ) Here is a cleaned up version. Where these 3 coordinates intersect in space is the actual center of gravity. Distance from Center of Gravity to Triangle Base Calculator. With the previous notations (ABC with a right angle on A and M as the midpoint of [BC]), the center of gravity G verifies \$ \overrightarrow{AG} = \frac{2}{3}\overrightarrow{AM}. Centre of gravity is the average position of all the points in a shape. It is easily divided into a square, triangle, and circle. 6 Center of Gravity. Center Of Gravity or known as COG is a momentum indicator used to identify potential reversal point when hitting the upper or lower extreme channel. The | {
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"lm_q2_score": 0.8418256512199033,
"openwebmath_perplexity": 304.50342906770857,
"openwebmath_score": 0.5220875144004822,
"tags": null,
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ros, catkin, catkin-package
Title: export gcc flags though catkin? CFG_EXTRAS?
I have the gcc c++0x flag set for a few of my packages. All the packages that depend on these package also needs the c++0x flag if they must not throw warning when the header files are processed.
Is there a way for catkin to export the flags? I saw the CFG_EXTRAS option for catkin_package(), Do I set the CFG_EXTRAS? What does it stand for?
Thanking you,
Benzun
Originally posted by Benny on ROS Answers with karma: 132 on 2014-06-18
Post score: 0
You can pass multiple "CMake configuration extra" files via catkin_package(CFG_EXTRAS) to be included when downstream packages find your package:
catkin_package(
CFG_EXTRAS ${PROJECT_NAME}-extras.cmake
) | {
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probability
Therefore, for this particle,
$$
S=-k\sum_{i=1}^{2} p_i\ln p_i = -k \left ( \frac{M_1}{M}\ln(M_1/M) + \frac{M_2}{M}\ln(M_2/M) \right )
$$
$$
= \frac{k}{M} \left ( M\ln M - M_1\ln M_1 - M_2\ln M_2 \right )
$$
If we take the Stirling approximation for the entropy of the overall system, then we get:
$$
S = k \ln \Omega = k \ln\frac{M!}{M_1!M_2!} \approx k \left[ M\ln{M} - M -(M_1\ln M_1 - M_1) -(M_2\ln M_2 - M_2) \right]
$$
$$
= k \left ( M\ln M - M_1\ln M_1 - M_2\ln M_2 \right )
$$
But this is just $M$ times the expression for the entropy of a single particle! So we are done. The two expressions for entropy are almost exactly identical. | {
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moveit, ros-hydro, arm-navigation
Title: robot_self_filter in hydro
I have a pointcloud from a laserscan and would like to filter out all points which belong to my robot itself. This could be done by the robot_self_filter, but as far as I know the whole arm_navigation stack which also includes this filter is deprecated since groovy. Is there any equivalent filter functionality in its successor MoveIt?
Originally posted by Tones on ROS Answers with karma: 635 on 2013-12-19
Post score: 0
I'm also looking for it. Check this:
http://answers.ros.org/question/69004/robot-self-model-filter-for-depth-sensor-in-ros-hydro/
also check my question about taking robot_self_filter out of MoveIt!
http://answers.ros.org/question/165676/take-3d-self-filter-out-of-moveit/
Originally posted by mark_vision with karma: 275 on 2014-05-16
This answer was ACCEPTED on the original site
Post score: 1 | {
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planets, atmospheric-science, gas
Still blue. Argon is colorless, and a thick enough layer of any colorless gas looks blue because it scatters shorter wavelengths more efficiently. On very rare occasions holes in different layers of Jupiter's clouds happen to line up, and thus provide a glimpse into clean hydrogen below. Such holes look blue (from outside).
Since that answer is for a planet orbiting a white star and you're asking about a yellow star, I would figure that your moon who have a blue-greenish tinted sky. Also, you state that nitrogen is present in the atmosphere, but as nitrogen gas is colorless (at least to humans), it wouldn't affect the sky color. The other gases you mention are in very small quantities, so their impact on the color of the sky would be unnoticeable. | {
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aqueous-solution, solubility
$\require{cancel}$
$$\pu{K_{sp}=K_s\;K_d=\ce{\cancel{\ce{[A_aB_b(aq)]}}}\times \ce{\frac{\ce{[A^{b+}]^a\;[B^{a-}]^b}}{\cancel{\ce{[A_aB_b(aq)]}}}}=\ce{[A^{b+}]^a\;[B^{a-}]^b}}$$
Which corresponds to the overall process:
$$
\require{cancel}
\begin{align}
\ce{A_aB_b(s)&<=>\cancel{\ce{A_aB_b(aq)}}} \tag{$K_s$} \\
\ce{\cancel{\ce{A_aB_b(aq)}}&<=>aA^b+(aq) +bB^a-(aq)}
\tag{$K_d$} \\
\hline
\ce{\ce{A_aB_b(s)}&<=>aA^b+(aq) +bB^a-(aq)}
\tag{$K_{sp}$} \\
\end{align}
$$
If $K_s$ is significantly higher than $K_d$, $K_{sp}$ would also be significantly higher, even though $K_d$ is small:
$$K_s>>K_d\implies K_{sp}>>K_{d}$$
The solubility $S$ of this salt could be calculated from the following expression, assuming no initial amounts of ions are present:
$$K_{sp}=(aS)^a\;(bS)^b$$
In conclusion, both $K_s$ and $K_d$ along with their respective equilibrium systems contribute to the solubility of the salt, and not just $K_d$ independently as one could wrongly assume. | {
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complexity-theory, graphs, shortest-path, weighted-graphs, network-flow
Title: Flow with edge-weight restrictions I am given a graph $G=(V,E)$ undirected and two vertices, the source vertex $s$ and the target vertex $t$. Additionally, each edge comes with a capacity $c(e)$ (non-negative) and a set of weight functions $w_1(e),...,w_k(e)$. To simplify things, assume these weight functions are non-negative as well. I am also given a set of upper bounds $l_1 ,...,l_k$.
The weight of a set of edges under any $w_i$ is additive. Denote $\tilde{E}$ as the set of edges (from the original graph) with positive flow (not back edges with the reverse flow, and not edges with a flow of zero). I would like to find the maximal flow between $s$ and $t$ such that $w_i (\tilde{E} ) \leq l_i$ for all indices $i$.
In other words, I am trying to find a flow under constraints for the edges that are being used.
I'm assuming this problem, as described, might be too hard to tackle. In this case, some assumptions can be made: | {
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chemical-potential, kinetic-theory
For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces. Only a small proportion of the molecules meet these criteria, so the rate of evaporation is limited. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid, thus, decreases. | {
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python, python-3.x, web-scraping, asynchronous
return files
async def place_file(source: str) -> None:
async with aiohttp.ClientSession() as session:
file_name = source.split('/')[-1]
file_name = urllib.parse.unquote(file_name)
r = await session.get(source, ssl = False)
content = await r.read()
async with aiofiles.open(folder + file_name, 'wb') as f:
await f.write(content)
async def main():
tasks = []
urls = await fetch_download_links('https://digital.nhs.uk/data-and-information/publications/statistical/mental-health-services-monthly-statistics')
for url in urls:
tasks.append(place_file(url))
await asyncio.gather(*tasks)
folder = 'C:/Users/<User>/OneDrive/Desktop/testing/' | {
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black-hole, cosmology, milky-way
Partly because ECSK made an assumption that fermions (loosely describable as "matter particles") have a spatial extent (tiny, but about 37 times the Planck length) that's incompatible with a renormalization technique useful in quantum mechanics (which generally requires all subatomic particles to be pointlike), and perhaps partly because its application to cosmology allows a universe that's eternal to the past and to the future rather than one that's eternal only to the future, the ECSK theory has not been widely utilized in cosmology until recently, when physicists exasperated with the failure to discover any specialized subatomic particle that would cause inflation began turning to it. As you can see on p.7 in the piece I've linked you to, Poplawski's torsion-based cosmology may be falsified if there's no evidence for any prevalent direction of rotation, whereas inflationary cosmology that's based on a field of hypothesized "inflaton" particles cannot be falsified at all, leading to | {
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"tags": "black-hole, cosmology, milky-way",
"url": null
} |
### Show Tags
04 Nov 2012, 11:24
2
sanjoo wrote:
Will we not change 8 to 6??
because if we have taken out those 2 cards..then ramining will be 6
6/46?
Read the question carefully. These 2 cards dont represent the stocks. Hence the 8 cards that represented stocks are still there, i.e. those 8 cards are still intact. But total number of cards has reduced from 48 to 46. Hence, probability can be found easily.
Hope that helps
-s
_________________
Intern
Joined: 16 Aug 2013
Posts: 4
Re: Probability Question [#permalink]
### Show Tags
16 Aug 2013, 20:19
VeritasPrepKarishma wrote:
rajman41 wrote:
Can we directly substract 2 cards out of 48 and reach the probablity of getting 8/46?
Yes you can. You already know that the first 2 cards are not stock cards. It's like we placed them face up. They anyway are out of the picture. Now we have 46 cards and 8 of them are stock cards. So the probability that the card we pick is a stock card is 8/46 = 4/23. | {
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proteins, gel-electrophoresis, western-blot
Why use a secondary antibody? Two reasons: - firstly, there will sometimes be a degree of amplification if more than one secondary antibody molecule binds each primary antibody molecule; but more important is that it means that it is not necessary to produce an enzyme conjugated form of every primary antibody, which is time-consuming and quite tricky. So in your work you may be studying several different proteins using Westerns, but you will be able to use the same secondary antibody to detect all of them.
Pore size
That should be 0.45 - 0.5 µm. Pore sizes are measured in micrometres. | {
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the simple square root property quadratic equations, quadratic formula with this step-by-step guide: quadratic calculator! Set y=0 would enter 1, now you have to find the of... + bi you should be able to even calculate imaginary solutions c values of,... Tools in mathematics quadratic function, we set y=0 sites online provide quadratic equation has real. Wide variety of applications across many disciplines you plugged the values in the form ax 2 + bx c.! However, at first, take the equation and they can not be ‘ 0.... Comes to solving quadratic equations ( manually ) so, the vertex of parabola h... 'S Mode to a + bi you should be able to: quadratic formula calculator. From quad '' meaning square, as there is no ax² term in! = 1, 5 and 6 will give you a step by step solution that is easy use... Solver is quite easy to use and loaded with smart and user-friendly interface calculator show the discriminant is,! Once you entered the values in the equation is linear, not quadratic, but | {
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python, beginner, object-oriented, tic-tac-toe
My understanding is that Tic Tac Toe is a type of game, not a type of board, but it does use a board as an internal state. Also, the game Tic Tac Toe doesn't manipulate itself. Instead, players manipulate the state of the game by making taking turns.
Therefore, my advice about how to organize this code from a object oriented point of view would be to create classes like (parenthesis indicate a class' superclass): Game, TicTacToe(Game), Board, Player, Human(Player), Computer(Player), Turn, and Move. Then, each Game would have a set of Turns, each with a corresponding Move and Player. Moves would affect the state of the Board within the Game instance. The kind of Moves that are allowed depend on the rules defined by the subclasses of Game (TicTacToe in this instance). Depending on the kind of Player, the Move for each Player's Turn could be generated automatically (for a Computer), or through keyboard/mouse input (for a Human). | {
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conformal-field-theory
For example, there are nice classes of two-dimensional conformal field theories (I mean "minimal models" etc.) that are almost uniquely (up to several integer-valued labels) determined by the conformal symmetry. All the dynamics – correlators etc. – of these CFTs are fully encoded by the OPEs which means that all this dynamics is fully encoded in the coefficients $c_{ijk}$. These coefficients may be calculated as solutions to the constraints equivalent to the conformal symmetry. Once you calculate them, you should view them as a major part of the definition of the CFT – they're the most fundamental numbers defining the identity of the CFT so it's futile to try to calculate them from something more fundamental. | {
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ros, ros-kinetic, joints
Title: General understanding of ros-canopen
Hello,
over the last couple days i tried to understand the concept of ros-canopen.
I do have a drive motor from dunkermotor which conforms to CiA 402. Also i do have a PEAK-USB adapter to connect the motor to my PC.
From my understanding ros_canopen provides a driver for PEAK-USB in the package socketcan_interface. After some preperation i should be able to test my setup with can-utils.
For usage with other ROS nodes i have to use either canopen_chain_node or canopen_motor_node whereby canopen_motor_node implements the CiA 402 profiles. For configuration i have to follow the description on canopen_chain_node/Configuration. I guess i only have to set a single node here since i only want to drive a single motor for testing purposes. The .eds/.dcf files should be provided by the manufacturer of my motor right? If not, can i write it by myself? | {
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waves, differentiation, string, calculus, continuum-mechanics
Title: How to calculate wave equation from a stretched string? I am reading "Introduction to Electrodynamics" [Griffiths] and in section 9.1.1, there is an explanation for why a stretched string supports wave motion. It begins as follows:
It identifies 2 points, $z$ and $z + \Delta z$ in in the direction that the wave is propagating, and states the net transverse force on the segment between $z$ and $z + \Delta z$ is:
$\Delta F = T (sin\Theta' - sin\Theta)$
so far so good. Then, provided that the distortion of the string is not too great, tan can replace sine because the angles will be small so:
$\Delta F \cong T (tan\Theta' - tan\Theta) = T(\frac{\partial f}{\partial z} - \frac{\partial f}{\partial z})$
where each of the above partial derivatives are taken at points $(z + \Delta z)$ and $z$ respectively.
The next step I am unclear on the reasoning for. It says:
$T(\frac{\partial f}{\partial z} - \frac{\partial f}{\partial z}) \cong T \frac{\partial ^2 f}{\partial z^2} \Delta z$ | {
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electrochemistry, electricity
I'd appreciate it if anyone could proof-read those points. Also I have doubts whether the Solid-Liquid Junction can also be called the Helmholtz Double Layer.
I made these points in class, and I let my teacher go through them, and he's in agreement with them, so I don't think this is a case of talking down the points wrong, at least not with respect to what was mentioned in class.
Now I asked my teacher, Q1: Screw the partition. Why not simply have the two half cells in separate compartments kept at a distance from each other, instead of using a 'partial' barrier like the porous asbestos partition? Wouldn't that eliminate the possibility of a Liquid-Liquid Junction being formed? | {
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javascript, gulp.js
// Complied JS dir
var targetJSDir = 'public/js';
// highlight error messages on error
var onError = function (err) {
gutil.log(gutil.colors.red(err));
};
/**
* Compile Sass, autoprefix CSS3,
*
*/
gulp.task('css', function() {
return gulp.src(sassDir + '/frontend.scss')
.pipe(plumber({
errorHandler: onError
}))
.pipe(sass({ style: 'compressed' }))
.pipe(autoprefix('last 10 version'))
.pipe(gulp.dest(targetCSSDir))
.pipe(notify('Sass compiled, CSS compressed!'))
}); | {
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the directions of the tangents to the curve at points P0 and P3, interpret your results. To use this calculator, a user just enters in the (r, φ, z) values of the cylindrical coordinates and then clicks 'Calculate', and the cartesian coordinates will be automatically computed and Vorticity { Stream function Solver in Cylindrical Coordinates L. Adjust the sliders to see how the surface depends on each parameter. ) This is intended to be a quick reference page. We will be mainly interested to nd out gen-eral expressions for the gradient, the divergence and the curl of scalar and vector elds. curl c rec b grad c rec b 10x p 2 W y d p ¥ s • 5z d d d (13) 6. As Roger Stafford points out, they need to be cartesian for the curl function. Coordinate Systems in Electromagnetism. The cylindrical coordinate system is convenient to use when there is a line of symmetry that is defined as the z axis. Finding the curl of the vector field and then evaluating the double integral in the parameter when | {
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The first step is to turn the system $M\bold{x} = \bold{0}$ to row-reduced echelon form.
Can you do that first?
3. Originally Posted by ThePerfectHacker
Let $M$ be that matrix if you define $T: \mathbb{R}_4 \to \mathbb{R}_5$ by $T(\bold{x}) = M\bold{x}$ you get a linear transformation.
The nullity of $T$ is $\text{dim} \left( \{ \bold{x}\in \mathbb{R}_4 |T(\bold{x}) = \bold{0} \} \right)$.
The first step is to turn the system $M\bold{x} = \bold{0}$ to row-reduced echelon form.
Can you do that first?
Ok i tried reducing it, and this is what i got:
[1 0 1 -2]
[0 1 -4 -2]
[0 0 0 8]
[0 0 0 16]
[0 0 0 8]
4. Originally Posted by LooNiE
Ok i tried reducing it, and this is what i got:
[1 0 1 -2]
[0 1 -4 -2]
[0 0 0 8]
[0 0 0 16]
[0 0 0 8]
When you have the system $M\bold{x} = \bold{0}$ and you are solving for $\bold{x}$.
The matrix you end up with is actually:
$\begin{bmatrix} 1&0&1&-2&0 \\ 1&1&-3&4&0 \\ 3&1&-1&0&0 \\ 4&2&-4&4& 0 \\ 0&1&-4&6&0 \end{bmatrix}$ | {
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"openwebmath_perplexity": 784.6609554253587,
"openwebmath_score": 0.9075717926025391,
"tags": null,
"url": "http://mathhelpforum.com/advanced-algebra/69409-kernel-transformation.html"
} |
planetary-formation
Rocky worlds will never grow as large as Jupiter. The greater mass will prevent it, and past a certain mass, a rocky world is unlikely to remain what we consider rocky. Above a certain mass it holds onto hydrogen which is the most abundant gas in the universe, and that would give the massive rocky world an appearance more like a gas giant. | {
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ros, rosinstall, catkin-workspace
use docker: re-use an existing image that has either no ROS, or a standard install. See wiki/docker.
if you're not comfortable with docker, you could use a chroot to essentially achieve the same, but with some more work. See wiki/ROS/Tutorials/InstallingIndigoInChroot (replace 'Indigo' with whatever release you're targeting).
As with both options you essentially get a 'clean slate', you can now check whether your .rosinstall file is complete.
PS: you probably know this, but a .rosinstall file is typically only used as a convenient way for your users to checkout many packages from source at once. If you just want to distribute a single package (or a single repository with multiple packages), and those packages depend only on other released packages, then it would be more convenient to either release your packages, or declare all dependencies in their manifests (package.xml) and have your users execute
rosdep install --from-paths /path/to/catkin_ws/src --ignore-src --rosdistro $DISTRO | {
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electrical-engineering
Title: Relation of Digital Logic Design to Electrical Power Engineering? I'm an undergraduate student of Electrical Power Engineering currently in 3rd semester, one of the courses we study is Digital Logic Design(dld) and I have found much interest in it but I am unclear whether the subject would have application in our field i.e. power engineering or not....Could anyone guide me that how should I study dld with what things in mind related to future perspective? Below is a job description for a Senior Electrical Engineer position at Princeton power systems to help you with future perspective. Princeton Power System makes power inverters for the Renewable Energy market. As you would see few key words that address the relationship between Digital Logic Design and Electrical Power Engineering.
FPGA – Field Programmable Gate Array
Power Electronics
Microprocessors | {
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Why? .Who knows? .Math is filled with little "jokes" like that.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Is there any proof of this trivia?
8. Hello, malaygoel!
Is there any proof of this trivia?
We want to evaluate: .[1] .$\displaystyle S\;=\;\frac{F_1}{10^2} + \frac{F_2}{10^3} + \frac{F_3}{10^4} + \frac{F_4}{10^5} + \frac{F_5}{10^6} + \hdots$
Multiply by 10: .[2] .$\displaystyle 10S\;=\;\frac{F_1}{10} + \frac{F_2}{10^2} + \frac{F_3}{10^3} + \frac{F_4}{10^4} + \frac{F_5}{10^5} + \hdots$
Add [1] and [2]: .$\displaystyle 11S\;=\;\frac{F_1}{10} + \frac{F_1+F_2}{10^2} + \frac{F_2+F_3}{10^3} + \frac{F_3+F_4}{10^4} + \frac{F_4+F_5}{10^5} + \hdots$
. . which gives us: .[3] .$\displaystyle 11S\;=\;\frac{F_1}{10} + \underbrace{\frac{F_3}{10^2} + \frac{F_4}{10^3} + \frac{F_5}{10^4} + \frac{F_6}{10^5} + \hdots}$
Examine that last portion . . . | {
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the basis? b. (1) Write down primitive lattice vectors for the 2-dimensional rectangular lattice, with sides aand bin the xand y-directions respectively, and a face-centred rectangular lattice, with a conventional cell of the same dimensions. Body-centered and face-centered cubic crystal systems. The lattice can therefore be generated by three unit vectors, a 1, a 2 and a 3 and a set of integers k, l and m so that each lattice point, identified by a vector r, can be obtained from:. Show that the reciprocal lattice of the 3D hexagonal lattice is another hexagonal lattice rotated by 30 degrees with respect to the original. G is called a reciprocal lattice vector. Consider a rectangular lattice in two dimensions with primitive lattice vectors $(a,0)$ and $(0,2a)$. 3) : Figure 1. Even today, in some texts the Hexagonal lattice with two interior points is shown in the Trigonal class. Crystal is a three dimensional periodic array of atoms. The lattice is continued n times from the original | {
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} |
This says that the flow along some edge does not exceed that edge's capacity. ow, called arc capacity. For general (not planar) graphs, vertex capacities do not make the maximum flow problem more difficult, as there is a simple reduction that eliminates vertex capacities. Edge capacities: cap : E → R ≥0 • Flow: f : E → R ≥0 satisfying 1. • The maximum value of the flow (say source is s and sink is t) is equal to the minimum capacity of an s-t cut in network (stated in max-flow min-cut theorem). I R ‚ 0 s t 2/2 1/1 1/0 2/1 1/1 G oal: † compute a °ow of maximal value, i.e., † a function f: E! In this section, we consider the important problem of maximizing the flow of a ma-terial through a transportation network (pipeline system, communication system, electrical distribution system, and so on). Given a graph which represents a flow network where every edge has a capacity. We are also able to find this set of edges in the way described above: we take every edge with the starting point | {
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"openwebmath_score": 0.6975939869880676,
"tags": null,
"url": "http://mrsfarley.net/a4m7zj/f5b37a-maximum-flow-problem-with-vertex-capacities"
} |
moreover
have $$\forall x\in H.\ \forall y\in H.\ \forall z\in H.\ x\oplus y\oplus z = x\oplus (y\oplus z)$$proof
from monoidAsssum have $$\forall x\in G.\ \forall y\in G.\ \forall z\in G.\ x\oplus y\oplus z = x\oplus (y\oplus z)$$ using IsAmonoid_def , IsAssociative_def
with A2 show $$thesis$$
qed
moreover
from A1 have $$\forall x\in H.\ \forall y\in H.\ \forall z\in H.\ x\oplus (y\oplus z) = g\langle x,g\langle y,z\rangle \rangle$$ using IsOpClosed_def , restrict_if
ultimately show $$thesis$$
qed
moreover
have $$\exists n\in H.\ (\forall h\in H.\ g\langle n,h\rangle = h \wedge g\langle h,n\rangle = h)$$proof
from A1 have $$\forall x\in H.\ \forall y\in H.\ x\oplus y \in H$$ using IsOpClosed_def
with A2, A3 have $$\forall h\in H.\ g\langle e,h\rangle = h \wedge g\langle h,e\rangle = h$$ using group0_1_L5
with A3 show $$thesis$$
qed
ultimately show $$thesis$$ using IsAmonoid_def , IsAssociative_def
qed | {
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"url": "https://isarmathlib.org/Monoid_ZF.html"
} |
navigation, simulation, rviz, stage, ros-fuerte
...
<!-- Run the map server (section inside the launch file) -->
<node name="map_server" pkg="map_server" type="map_server" args="$(find Navigo)/world/our_world.pgm 0.12"/>
...
</launch>
The definition of this resolution parameter is:
Resolution of the map, meters/pixel
Therefore we measured the corridor width, which is 1.85m,
and the same spot inside the given our_world.pgm file which has 36pixels.
This leads to a resolution of:
1.85m/36pixels = 0.0514
But if we set this value instead of the 0.12 in our launch file, our robot is much to large inside the Rviz map.
The question is how to find the correct value or if there is another way of "sycronizing" these map resolutions.
Do we have to change some parameters inside the world file or the Rviz our_world.vcg file?
Here is our our_world.world file:
define block model
(
size [0.5 0.5 0.5]
gui_nose 0
)
define topurg ranger
(
sensor(
range [ 0.0 5.0 ]
fov 240
samples 666.7
) | {
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} |
c++, time-limit-exceeded, c++14
Sample Output
25
1750
444444445222222222
Explanation
In the first sample case, the city had 5 buildings, and the first building has height 10 and the second building has height 7. We know the third building either had height 17 or 3. One possible sequence of building heights that minimizes the sum of heights is {10, 7, 3, 4, 1}. The sum of all heights is 10+7+3+4+1 = 25.
In the second sample case, note that it's possible for some buildings to have height zero.
Environment
Time Limit: 5.0 sec(s) for each input file.
Memory Limit: 256 MB
Source Limit: 1024 KB | {
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notation, mathematical-foundations
Title: What Does The Notation of Union Over K represent? I am currently studying about polynomial time in Comp Theory. The definition for polynomial time given in my textbook as follows:
$$P= \bigcup_{k}TIME(n^k)$$
I have not seen the Union over k notation before. K is a constant. A quick introduction to the meaning of this notation would be enormously helpful.
Thank you Authors often leave out the domain of the union if it is clear within the context. Here, $k$ is a natural number, i.e. $P = \bigcup\limits_{k \in \mathbb{N}} TIME(n^k) $. This is what it means for a complexity function to be bounded by a polynomial: there is a constant $k$ such that the function is in $\mathcal{O}(n^k)$. | {
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"url": null
} |
java, json, generics, gson
Personally I do not even want to see annotations that are specific to certain storage mechanism in a data objects (and I am aware that it is a level of fundamentalism not shared by many people). Why should the data object know about the storage mechanism? Data should not be aware of how or where it is stored. That is the responsibility of the persistence layer. And once the persistence layer changes to the newest fashionable serialization format, all the data objects would have to change even though their main purpose and responsibility has not changed a bit.
Because your ISaveable interface requires the Path parameter it is also very limited in where the data can be stored. E.g. everything has to go to a file in a file system. Should someone want to store the data to a generic OutputStream, a completely different implementation has to be written, so the framework isn't very flexible. | {
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} |
quantum-mechanics, condensed-matter, topological-phase
direction commute, so that $L_x L_y = 2\pi N_{\Phi} \ell^2$ ($\ell$ is the magnetic length). We can write down wavefunctions $\psi_{\mathbf{k}}(x,y)$ that statisfy these boundary conditions, as done, for example, by Yoshioka (http://prb.aps.org/pdf/PRB/v29/i12/p6833_1) and Haldane and Rezayi (http://prb.aps.org/pdf/PRB/v31/i4/p2529_1). To calculate the Berry curvature, one could simply calculate the Berry connection in some gauge, | {
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planetary-science, mantle, moon, isotopic
... which was formed by a celestial collision over four billion years ago. With a diameter of 2,500 km and a depth of about 13 km, the basin is the moon’s oldest and largest impact crater. Very large impact craters can potentially penetrate through the crust and enable probes to sample the lunar mantle.
... the lunar soil at the landing area contained a large amount of olivine, low-calcium pyroxene and a small trace of high-calcium pyroxene, which are very likely from the lunar mantle.
Notice the term "very likely" near the end of that quote.
If no one has ever seen it, how do we know what the lunar mantle looks like? | {
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regression, prediction, sequence
b. You can use your scoring system, not as an objective function, but as a metric to select the best model on a hyper-parameter search.
c. With this approach you can use many standard sequence learning models, such as LSTM (if you have enough data). Or you could just use a single step prediction model that you feed current prediction plus any other features of the sequence that is allowed to know, and generate sequences from it by calling it repeatedly.
This system should encourage re-tries that get closer to the true value.
2. Use your scoring system directly as a learning goal
This will require some alternative optimising framework to gradient descent around the prediction model (although some frameworks can generate gradients internally). Genetic algorithms or other optimisers could be used to manage parameters of your model, and can attempt to change model parameters to improve results. | {
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c#, .net
static private void Translate(ToolStripItem o, string lang)
{
string str = TranslateString(o.Name, lang);
if (str != null)
o.Text = str;
}
static private void Translate(Form o, string lang)
{
string str = TranslateString(o.Name, lang);
if (str != null)
o.Text = str;
}
/// <summary>
/// returns the <c>name</c> string from the <c>lang</c> resource
/// </summary>
/// <param name="name">string/key name</param>
/// <param name="lang">the language to translate to</param>
/// <returns>a translated string for <c>name</c></returns>
static public string TranslateString(string name, string lang)
{
if (lang_ci == null || !lang_ci.TwoLetterISOLanguageName.Equals(lang))
lang_ci = new CultureInfo(lang); | {
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particle-physics, energy, conservation-laws, antimatter, neutrons
Energy in the elementary particle level needs a carrier, either a gauge boson, i.e. photon for electromagnetic interactions, a W/Z for weak, gluon for strong, or particles in general as seen in the standard model.
A neutron is a combination of three quarks . A complicated system of conservation laws rules in the microcosm, in addition to energy conservation: from baryon number conservation to charge conservation to lepton number, to color conservation. The three quarks of the neutron have to be balanced with three antiquarks to keep the conservation laws. Thus the carrier that will allow the generation of a neutron cannot generate it singly, even if it is a gluon or gluons of enough energy. It would have to generate the antiquarks too. | {
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evolution, phylogenetics, visualization, publishing
Title: How should I put a large phylogeny into a scientific paper? I've been trying to put a phylogeny tree into a scientific paper. This tree includes ~220 species, which is too too large for one page for journal articles (Letter or A4 size). But in my paper it is crucial to show the whole tree on which the among-species distribution of a characteristic is indicated. I have looked up some journal issues but so far haven't found any similarly large phylogeny in one article. How do people usually treat this kind of situation in scientific papers? Could anybody tell me how to do it, or show me examples? Thank you so much. Also, don't forget that you can deposit your full tree in treebase. So you can show the collapsed tree in the paper, and give a link to the full tree somewhere in the text. | {
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mass, density
Title: Calculating mass from the integration of the surface density of a disc If I had an equation for the surface density of a disc as a function of it's radius, such as:
$$
\Sigma = A\left(\frac{r}{B}\right)^{1/2}
$$
where A and B are constants, and I want to find the mass, what form does the integration take?
Would it be:
$$
M = AB^{-1/2}\int{r^{1/2}} r dr
$$
Do I add in that extra r since its a disc/cylinder? I get an answer for the mass in the right ballpark if I do but I'm not sure I can justify adding it in, or whether it should be a double integral.
Thanks for any help. To give a full answer, yes you do need to do a double integral, but in this case, one of the double integrals is easy to evaluate if you switch to polar coordinates. The factor of $r$ arises when you switch to polar coordinates. | {
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python
@property
def source_object_location(self):
return self.object_location
@property
def destination_path_prefix(self):
return f"{self.source_bucket}/{self.date}"
@property
def destination_object_location(self):
return (f"{self.destination_path_prefix}/{self.source_object_filename}"
)
def _get_datasets(self):
if self.source_object_extension == "xlsx":
return None
else:
return self._match_inbound_csv_to_dataset()
Now we have way fewer methods. While we're here, I've utilized pathlib.Path to take advantage of some convenience functions.
Repeated regexes
It might be useful to cache repeated regexes here:
class FileMetadata:
dataset_cache = {}
def __init__(self, ...):
~snip~
def _match_inbound_csv_to_dataset(
self,
):
datasets = []
for dataset in ACTIVE_DATASETS:
name, regex = dataset.name, dataset.file_match_regex | {
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ros
Title: "apt-get source" for packages.ros.org?
Where are the sources (*.orig.tar.gz, *.diff.gz, and *.dsc files) for the debs on packages.ros.org?
Specifically, how to make "apt-get source" do the right thing for packages from this repository? Adding the obvious deb-src line to ros-latest.list doesn't seem to help (see below). Poking around on the packages.ros.org http interface, it looks to me like the sources have not been uploaded.
Packages I care about include ROS dependencies like assimp, yaml-cpp, and eigen. For example,
$ apt-cache policy libassimp2
libassimp2:
Installed: 2.0.0.6-ubuntu1~lucid1
Candidate: 2.0.0.6-ubuntu1~lucid1
Version table:
*** 2.0.0.6-ubuntu1~lucid1 0
500 http://packages.ros.org/ros/ubuntu/ lucid/main Packages
100 /var/lib/dpkg/status
$ cat /etc/apt/sources.list.d/ros-latest.list
deb http://packages.ros.org/ros/ubuntu lucid main
$ apt-get source libassimp2
Reading package lists... Done
Building dependency tree | {
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sql, sql-server, delphi, adodb
implementation
{ ESQLExecScriptError }
constructor ESQLExecScriptException.Create(const Msg: string;
const ErrCode: Integer; ABlock: TSQLExecBlock);
begin
inherited Create(Msg);
ErrorCode := ErrCode;
FBlock:= ABlock;
end;
{ TSQLExecBlock }
constructor TSQLExecBlock.Create(AOwner: TSQLExecBlocks);
begin
FOwner:= AOwner;
FSQL:= TStringList.Create;
FStatus:= sePending;
FMessage:= '';
end;
destructor TSQLExecBlock.Destroy;
begin
FSQL.Free;
inherited;
end;
function TSQLExecBlock.GetIndex: Integer;
begin
Result:= FOwner.FItems.IndexOf(Self);
end;
function TSQLExecBlock.GetSQL: TStrings;
begin
Result:= TStrings(FSQL);
end;
procedure TSQLExecBlock.SetSQL(const Value: TStrings);
begin
FSQL.Assign(Value);
end;
{ TSQLExecBlocks }
constructor TSQLExecBlocks.Create(AOwner: TSQLExec);
begin
FOwner:= AOwner;
FItems:= TList.Create;
end;
destructor TSQLExecBlocks.Destroy;
begin
Clear;
FItems.Free;
inherited;
end; | {
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lagrangian-formalism, gauge-theory, maxwell-equations, gauge
Title: Are Maxwell's equations "physical"? The canonical Maxwell's equations are derivable from the Lagrangian
$${\cal L} = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu} $$
by solving the Euler-Lagrange equations.
However: The Lagrangian above is invariant under the gauge transformation
$$A_\mu \to A_\mu - \partial_\mu \Lambda(x) $$
for some scalar fiend $\Lambda(x)$ that vanishes at infinity. This implies that there will be redundant degrees of freedom in our equations of motion (i.e. Maxwell's equations).
Therefore, as I understand gauge fixing, this implies that Maxwell's equations (without gauge fixing) can lead to unphysical predictions.
Question: Hence my question is simply are Maxwell's equations (the ones derived from $\cal{L}$ above) actually physical, in the sense they do not make unphysical predictions?
Example: The general solution to the equations of motion derived from $\cal{L}$ is given by | {
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c++, console, formatting, ascii-art
std::string ConsoleTable::getRows(Rows rows) const {
std::stringstream line;
for (int i = 0; i < rows.size(); ++i) {
line << style.vertical;
for (int j = 0; j < rows[i].size(); ++j) {
std::string text = rows[i][j];
line << space * padding + text + space * (widths[j] - text.length()) + space * padding;
line << style.vertical;
}
line << "\n";
}
return line.str();
}
std::ostream &operator<<(std::ostream &out, const ConsoleTable &consoleTable) {
out << consoleTable.getLine(consoleTable.style.top);
out << consoleTable.getHeaders(consoleTable.headers);
out << consoleTable.getLine(consoleTable.style.middle);
out << consoleTable.getRows(consoleTable.rows);
out << consoleTable.getLine(consoleTable.style.bottom);
return out;
} | {
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javascript, react.js, redux
Title: Abstracting async hooks out from components A component displays a list of values and I'm trying to hide everything about how those values are gotten, essentially divorcing concerns about state away from the component itself so that in the future any changes to which API data is fetched from, what store is used, etc won't effect the component.
First, is this a good idea at all or should mount/unmount actions be handled directly in the component?
Second, if it is a good approach, how is my implementation? I'm feeling comfortable in JS but am not an expert
ContentList.js:
import React from 'react'
import './ContentList.css'
import { ContentCardContainer } from '../ContentCard/ContentCard'
import { getPostSummaries } from '../../Utils/ContentAPI'
import { Grid } from '@material-ui/core'
export function ContentListContainer(props) {
const posts = getPostSummaries()
return <ContentList posts={posts} />
} | {
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electromagnetism, electric-circuits, time, electromagnetic-induction
Thanks in advance,
(Okay it isn't working right now, but I think the directions are as I stated above.)
Edited according to the clarification suggested by Philip Wood. When you flip on the light switch, a surge of current suddenly flows out of the house mains and into the light assembly. This sudden surge causes the mains voltage to momentarily dip down and then spring back to normal levels.
The "dip down and spring back" is called a glitch or a surge and all the AC mains wiring in your house will serve as an antenna to broadcast the glitch as if it were a radio signal.
If another appliance nearby lacks sufficient RF shielding to block the radiated glitch from getting into its circuitry, then that circuitry can be upset or scrambled by the glitch and cause the appliance to malfunction. | {
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gene, ensembl
By start and end position, I refer to the start and end values given in the "fields" section here and the file from which I want to parse the values is the second last file available in this link.
For instance, the end - start value of the gene with ensembl id ENSG00000131482,
gene :G6PC
Edit 2: I get the gene names and the expression values from the SOFT files documented in GEO, link
The following is a sample output from SOFT file. It gives me the probe_set(ID_REF) , Gene name and expression values from samples (GSMXXXXXX). Here we see fro G6PC, values are reported from two probe_sets. Can we get the transcript id's from the probe_sets?
Obtaining the transcript id will help me in finding the length of the specific transcript.
> Table(gds)[2449,0:5]
ID_REF IDENTIFIER GSM388749 GSM388750 GSM388753
2449 1555612_s_at G6PC 4.39472 4.52235 4.26869
> Table(gds)[16399,0:5]
ID_REF IDENTIFIER GSM388749 GSM388750 GSM388753 | {
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java, animation, physics, processing
Title: Java snow animation I was inspired by this to write a graphic snow animation in Java/Processing. It works great, but it has some design issues.
The full project is here on github;
Main
package com.jatkin.snowday;
import processing.core.PApplet;
import processing.core.PGraphics;
/**
* Created by Jarrett on 02/04/16.
*/
public class Main extends PApplet {
public static void main(String[] args) {PApplet.main(Main.class.getCanonicalName());}
final int backgroundColor = color(0, 146, 178);
final World world = new World();
/**
* Processing 3 has changed the basic format for starting an app from raw
* java. Size now must be called from `settings`.
*/
@Override
public void settings() {
size(500, 300, FX2D);
}
@Override
public void draw() {
fill(255);
noStroke();
background(backgroundColor);
world.tick(sketchWidth(), sketchHeight());
world.render(getGraphics());
}
} | {
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c#, object-oriented, design-patterns
Yes I agree that there is some duplicated code that could be refactored into methods. However that might be for another post.
A full attempt at refactoring based on the suggestions above shows:
var size2s = Finallist.Select(x => x.Size2.ToString()).Distinct().ToList();
size2s.Insert(0,"");
string oldSize2Value = cmbSize2.Text;
_noise = true; // cause the handler to ignore the noise...
if (!_cmbSize2Selected)
{
cmbSize2.DataSource = Size2s;
}
cmbSize2.Text = oldSize2Value;
_noise = false; // let the event process again
var grammages = Finallist.Select(x => x.Grammage.ToString()).Distinct().ToList();
string oldGrammageValue = cmbGrammage.Text;
grammages.Insert(0,"");
_noise = true; // cause the handler to ignore the noise...
if(!_cmbGrammageSelected)
{
cmbGrammage.DataSource = grammages;
}
cmbGrammage.Text = oldGrammageValue;
_noise = false; // let the event process again | {
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quantum-information, quantum-measurements
Title: Uniqueness of representing POVM using projective measurement $\newcommand\tr{\operatorname{tr}}
\newcommand\ket[1]{\lvert#1\rangle}
\newcommand\bra[1]{\langle#1\rvert}
$[Skip to the conjecture for a self-contained mathematical formulation of the question.]
Given a POVM, there are always many possible way to implement that POVM as a nondestructive measurement. (In other words: There are different measurement processes that are described by the same POVM but that have different post-measurement states.) However, I need to know whether the following process leads to a unique post-measurement-state: | {
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complexity-theory, complexity-classes, factoring
Factoring is, of course, in $NP$ (function version being in $\mathcal{F}_{NP}$), so it should easily follow that anything polynomial time reducible to factoring is going to have a polynomial time verifier. If you were actually asking if any polynomial time verifiers share the same "hardness" as factoring, then the answer is: no idea. It would require making assumptions about whether or not factoring is in $P$.
I am afraid that I could not find a non-number theoretic set of problems that are known to be polynomial time reducible to factoring. Despite much study, the complexity of factoring is still very open. Knowing where it falls will provide many additional answers to your question. I'll go over what I have:
Two well known ones are computing Quadratic Residuosity and computing the Euler Totient, $\phi (n)$. The equivalence between factoring and Euler totient is very straight forward, especially to those that have ever looked into RSA. | {
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c++, linked-list
But this is still just at the idea state but will (probably) become part of how modern C++ will be written in the future.
Always Initialize members
City(){}; // Note: that ';' is not required.
Here you default initialize your members. Default initialization of pointers does nothing and leaves then in an indeterminate state.
Use Initializer list to initialize members
If you don't initialize members in the initializer list then they will be initialized using the default constructor before the body of the constructor is entered.
SO in this constructor.
City(std::string initName, City *initNext, City *initPrevious, std::string initMessage)
{
cityName = initName;
next = initNext;
previous = initPrevious;
message = initMessage;
} | {
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java, optimization, game
Why the / 60? What is the meaning of that? From what I can tell, frames is the count of draw() calls in a second. Why divide it by 60?
worse, dividing by 60 is an integer operation. You are doing massive truncation in this process.
Game Loop
You have three periodic events that are happening:
each second there is a special 'event'
each frame-period there is a 'draw'
each other time there is a 'tick'
Your loop is complicated, it uses nano-seconds for one timer, milliseconds for another, and it seems the timer for the 'tick' loop is broken....
Let's break your code down:
public void run () {
Fine, you're a runnable, in your own thread (which should have a name, by the way).
while (isRunning) {
OK, we loop until told not to.
// get delta time
currentTime = System.nanoTime ();
deltaTime += (currentTime - lastLoopTime) / OPTIMAL_TIME;
lastLoopTime = currentTime; | {
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lagrangian-formalism, calculus, constrained-dynamics
If they wrote $\nu\int_0^D (x'-\cos \theta) ds$, with only one $\nu$, they would only get $\int_0^D x' ds= \int_0^D \cos\theta ds$, which is not at all the same thing.
Look at problem 3 in this homework set for an example. In that problem the lagrenace multiplier for point with coordinate $s$ is the tension in the cable at that point. | {
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orbital-motion, earth, planets, celestial-mechanics, solar-system
Where while the Sun blocks the view of one planet for a while, it is not blocked forever. (Here, the eccentricity of the earth's orbit (0.01671) has been grossly exaggerated.)
We can crudely estimate how long after peri/aphelion it would take for one planet to be visible from the other by computing
$$t_{vis} \approx \frac{R_{*}}{v_{peri} - v_{aph}}\approx 8 \ \rm{ days}$$
This completely ignores the effect of non-circularity of the orbital path, but uses the differences in velocity.
We can check this result easily with an orbital simulation (code at end) and obtain the following result: | {
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gazebo, turtlebot, multiple, namespace, tf-prefix
Title: Multiple robots simulation and navigation
###How to launch multiple robots in gazebo simulator and how to setup navigation stacks for such a simulation?###
There were already some questions and answers for the subject, like: here, and here, and here. This is my question and answer to summarize the discussion in one place.
Originally posted by Jakub on ROS Answers with karma: 1821 on 2012-08-14
Post score: 43 | {
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inorganic-chemistry
Charge (larger charge = stronger enthalpy)
Size of ion (smaller ion = stronger enthalpy)
Now, because you are trying to bond M (alkali earth metals/group 2) to carbonates, then the charge is going to stay constant. This is because carbonates (CO3) will always have a charge of -2 and M will always have a charge of +2. So, we are going to forget about charges for your specific situation.
If you look downwards on a periodic table in G2, the ionic radius of alkali earth metals increases. The smallest, and thus the one that will result in the strongest lattice enthalpy, is Beryllium. The smaller ionic radii allow for tighter packing, which leads to greater lattice enthalpy values. | {
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c++, performance, game, api, event-handling
template<typename EventType>
inline void EventManager::unsubscribe(typename CallbackContainer<EventType>::SubscriberHandle handle) {
s_Callbacks<EventType>.removeCallback(handle);
}
template<typename EventType>
inline void EventManager::publishBlocking(const EventType& event) const {
s_Callbacks<EventType>(event);
}
template<typename EventType>
inline void EventManager::publishBlocking(EventType&& event) const {
s_Callbacks<EventType>(std::forward<EventType>(event));
}
template<typename EventType>
void EventManager::publishBus(const EventType& event) {
s_Callbacks<EventType>.save(event);
m_EventBus.emplace_back(&s_Callbacks<EventType>);
}
template<typename EventType>
void EventManager::publishBus(EventType&& event) {
s_Callbacks<EventType>.save(std::forward<EventType>(event));
m_EventBus.emplace_back(&s_Callbacks<EventType>);
} | {
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large-hadron-collider
In the RS model, the gravitons decay into pairs of Standard Model particle. According to the Particle Data Group review, the most stringent limits come from decays into dilepton and diphoton. Here too there is a Standard Model background, the so-called Drell-Yan process $pp \to \text{jet} + Z^0/\gamma$ and then $Z/\gamma \to l^+ l^-$ for the dilepton.
[1] https://arxiv.org/abs/1005.1805 | {
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thermodynamics, energy-conservation, temperature
This is restatement of the fact that the tea is hotter than the milk as the temperature of a substance depends on the average kinetic energy of the molecules which make up the substance.
When you mix the tea and the milk together the molecules of the tea and the milk collide and eventually reach an average kinetic energy (temperature) which is less than the average kinetic energy (temperature) of the tea before mixing and is greater than the average kinetic energy (temperature) of the milk before mixing.
So the collisions between the molecules redistribute the kinetic energy amongst the molecules and what is called thermal equilibrium is reached.
If there is no loss of heat or chemical reaction then the kinetic energy of the hot tea plus the kinetic energy of the cold milk is equal to the kinetic energy of the mixture but on average the tea molecules have less kinetic energy after mixing and the milk molecules have more kinetic energy after mixing. | {
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inorganic-chemistry, halides, transition-metals, oxidation-state
Title: Stability of 3d metal fluorides and iodides in different oxidation states I read that the fluorides of 3d metals in lower oxidation states, e.g. $\ce{VF2}$, $\ce{TiF2}$, and $\ce{CuF}$ are thermodynamically unstable. For example, $\ce{CuF}$ disproportionates to $\ce{Cu + CuF2}$, as described on Wikipedia.
On the other hand, their iodides tend to be more stable (so, for example, $\ce{CuI}$ can be easily obtained from a redox reaction between $\ce{Cu^2+}$ and $\ce{I-}$). Why is this the case? In general, iodides stabilise lower oxidation states and fluorides stabilise higher oxidation states, e.g. $\ce{CuF2}$ versus $\ce{CuI}$. This can be explained with some thermodynamics. Consider
$$\ce{M(s) + $\frac{n}{2}\,$X2 (g/l) -> MX_n (s)}$$
In order to form a halide salt with a higher oxidation state (i.e. larger $n$), you need to pay some energetic costs to get the metal to the higher oxidation state, namely: | {
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javascript, beginner, canvas
Degradation limit: How many can you add to a page before it degrades the page's performance metrics?
Are you planing on using significantly less than the degradation limit?
If you answer yes to the second then its safe to use. However do keep an eye out for more efficient components.
Rewrite
Removes noise and buggy code.
Moves default properties to a constant for easier maintenance and readability.
<script>
const KNOB_DEFAULTS = {
angleStart: -0.75 * Math.PI,
angleEnd: 0.75 * Math.PI,
colorFG: '#245166',
trackWidth: 0.4,
valMin: 0,
valMax: 100,
value: 40,
};
[pureknob.createKnob(100, 100), pureknob.createKnob(100, 100)].forEach(demoKnob);
function demoKnob(knob, i) {
for (const [name, val] of Object.entries(KNOB_DEFAULTS)) { knob.setProperty(name, val) }
document.getElementById('some_element_' + (i + 1)).appendChild(knob.node());
}
</script> | {
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python, open-ai, environment
Title: Advice on creating a new environment using OpenAI Gym I'm looking for some general advice here before I dive in.
I'm interested in creating a new environment for OpenAI gym to provide some slightly more challenging continuous control problems than the ones currently in their set of Classic Control environments. The intended users of this new environment are just me and members of a meetup group I am in but obviously I want everyone to be able to access, install and potentially modify the same environment.
What's the easiest way to do this?
Can I simply import and sub-class the OpenAI gym.Env module similar
to the way cartpole.py does.
Or do I need to create a whole new
PIP package as this article suggests? | {
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3. ### Solid Geometry
Find the Lateral area in cm square of the following right pryramid. 1. Base is regular octagon of side 20cm and altitude of 20cm. 2. Base is regular hexagon of side 20cm and altitude of 30cm. 3. Base is regular hexagon of side
4. ### Maths
A regular hexagon is to be cut from a sheet of diameter d.the width across corner is | {
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Use vpa to convert the symbolic solutions solx and soly to numeric form.
```vpa(solx)
vpa(soly)```
```ans =
[ 0.70095651347102524787213653614929, 2.4406361401187679905905068471302,...
-5.5822287937085612290531502304097, -3.8425491670608184863347799194288]
[ 0.15567910349205249963259154265761, 2.9859135500977407388300518406219,...
-6.1275062036875339772926952239014, -3.2972717570818457380952349259371]
ans =
[ 1.4151172233028441195987301489821, -4.8680680838767423573265566175769,...
-1.4151172233028441195987301489821, 4.8680680838767423573265566175769]
[ 0.86983981332387137135918515549046, -5.4133454938557151055661016110685,...
-0.86983981332387137135918515549046, 5.4133454938557151055661016110685]
```
### Simplify Complicated Results and Improve Performance
If results look complicated, solve is stuck, or if you want to improve performance, see, Resolve Complicated Solutions or Stuck Solver. | {
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"lm_q1q2_score": 0.8459285426460108,
"lm_q2_score": 0.8688267762381844,
"openwebmath_perplexity": 922.9804206597966,
"openwebmath_score": 0.5450394749641418,
"tags": null,
"url": "http://www.mathworks.com/help/symbolic/solve-a-system-of-algebraic-equations.html?nocookie=true"
} |
machine-learning, linear-regression, decision-trees, xgboost
Title: What is the implication of having features with less variation in a tree based model? I'm training a tree-based model (e.g. xgb). I have some features with more than 90% values constant. Does it add value to the model since the variation in the data is minimal?.
What would be the impact of the same if I were to use a linear regression model? Variation is not the key. Notice that 0/1 indicator variables are used frequently and might have mostly 0's (like many missing indicators). The key is where is the variation in relation to what you are predicting and in relation to interactions.
For example, if your column is 0 where target = 0 and not 0 where target = 1, then the variation does not matter. Add a new indicator feature where the original column is 0 or not 0 may be a good way. You might want to do this anyway. | {
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study time, and refine test-taking skills. AnalystPrep's Study Materials for the SOA IFM Exam. Our Investment and Financial Markets (IFM) question bank incorporates all of the concepts covered in the Society of Actuaries exam. ASM Products are sold at ACTEX Learning | Mad River Books and The Actuarial Bookstore. Thank you so much for helping me pass my first CFA exam.”. 11. We offer study materials for Exams P/1, FM/2, MLC, MFE/3F, C/4, S and EA-1, EA-2F and EA-2L, written by an outstanding team of authors. To succeed in exam IFM, you will need to solve numerous hard, mathematical practice questions on a number of different topics such as the Capital Asset Pricing Model (CAPM), market efficiency, derivative pricing, the BSM model, and much more. Are there free study materials out there for IFM? Actuarial Study Materials. Posted by 1 year ago. So, I … I cleared FRM Part I (May-2018) with 1.1.1.1. ASM Study Manual for Exam P - Actuarial Study Materials for Exam P, FM, IFM, LTAM, STAM, | {
"domain": "gridserver.com",
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quantum-mechanics, homework-and-exercises, angular-momentum, hamiltonian, commutator
And $$\hat{H}=\frac{-h^{2}}{4\pi^{2}(2m)}\Delta+\frac{1}{2}kr^{2}.$$
I've been trying to prove it using the very basic $[\hat{L^{2}},\hat{H}]f= \hat{L^{2}}\hat{H}f-\hat{H}\hat{L^{2}}f$ method of showing the commutation relationship. My first thought was that by applying $\hat{L^{2}}$ to $\hat{H}$ all the terms that are dependent on r or $\frac{r}{dr}$ would disappear, but if some arbitrary function f had cross terms, this isn't necessarily true, and the algebra got pretty messy after that. Is there a better way to prove this? You want to show that $[L^2,H]=0$. There are some ways to do this. The easiest and more direct one is to notice that in spherical coordinates
$$H = -\dfrac{\hbar^2}{2m}\dfrac{1}{r}\dfrac{\partial^2}{\partial r^2}r + \dfrac{1}{2mr^2}L^2+ V(r), $$ | {
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java, rags-to-riches
Title: Let's Break Down the Party This is a rags-to-riches question, the original is here: Coin dispenser program
There are three parts to this, a Denomination enum, a Calculator utility class and the unit test for it, using TestNG.
Please feel free to comment on any parts of the code, including comments.
Denomination enum
import java.math.BigDecimal;
import java.util.Objects;
public enum Denomination {
A_MILLION(1_000_000, "$1 million"),
FIFTY_DOLLARS(50, "$50"),
TWENTY_DOLLARS(20, "$20"),
TEN_DOLLARS(10, "$10"),
FIVE_DOLLARS(5, "$5"),
DOLLAR_NINETY_NINE(1.99, "$1.99"),
A_DOLLAR(1, "$1"),
QUARTER(0.25, "25¢"),
DIME(0.1, "10¢"),
NICKEL(0.05, "5¢"),
A_CENT(0.01, "1¢");
private final BigDecimal value;
private String description;
private Denomination(double value, final String description) {
this.value = BigDecimal.valueOf(value);
this.description = Objects.requireNonNull(description);
} | {
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average COST per share of shares currently held;}\text t = \text { TARGET average cost per share after purchase; and}\text m = \text { current MARKET price per share.}$Proof$t = \dfrac{ch + mp}{h + p} \implies ht + pt = ch + mp \impliespt - mp = ch - ht \implies p(t - m) = h * (c - t) \implies p = h * \dfrac{c - t}{t - m}.$Let's try it in your example.$p = 1200 * \dfrac{9.34 - 9.00}{9.00 - 8.50} = 1200 * \dfrac{0.34}{0.50} = 816.$Let's check. Your total cost after purchase =$1200 * 9.34 + 816 * 8.50 = 11208 + 6936 = 18144.$Your number of shares after purchase =$1200 + 816 = 2016.$The new average cost per share =$\dfrac{18144}{2016} = 9.00.$And that was your target. You may not always get an exact answer because you cannot buy fractional shares. First, thanks for your knowledge and time. Secondly, trying to commit this to memory might be beyond the scope of this forum but... Is there a way to summarize or better explain why we divide (c - t) by (t - m) or just a generalized statement in | {
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homework-and-exercises, newtonian-mechanics, forces, classical-mechanics, kinematics
However, assuming that the velocity does indeed remain constant, how do I approach the above problem. The given answer is $N=5mg$
In general, suppose I have a curve, and a value of velocity, which may or may not be constant, how exactly do I approach such problems where I'm asked to find normal reaction?
EDIT:
According to the comment and the answer, I've proceeded as follows :
$$k=\frac{\frac{d^2y}{dx^2}}{(1+(\frac{dy}{dx})^2)^{\frac{3}{2}}}$$
Since, $y=bx^2$, $y''=2b$, and $y'=2bx.$
At $x,y=0$, we have $k=2b$.
Plugging this back, we have $N=mkv^2$, where $v=\sqrt{\frac{2g}{b}}$
Thus, we have :
$$N=4mg$$
The stated answer is however $N=5mg$. Am I missing something here, or is my solution correct ? Let's assume that the speed is constant for now, it can be shown that, the "radius of a curve" is calculated as:
$$\rho = \frac{(1+f'(x)^{\frac{3}{2}} )}{f''(x)}$$
This is probably something for you to figure out why. | {
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python, parsing
Title: Python insert line in the middle of the file I will be inserting a new text line in a setup.py file, this new line will contain text, and is part of the REQUIRED_PACKAGES. I parsed the
file and look for REQUIRED_PACKAGES pattern (REQUIRED_PACKAGES = [ ... ]). Looking for alternatives during file insertion.
A sample setup.py file looks like this:
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import fnmatch
import os
import re
import sys
from setuptools import Command
from setuptools import find_packages
from setuptools import setup
from setuptools.command.install import install as InstallCommandBase
from setuptools.dist import Distribution
DOCLINES = __doc__.split('\n')
_VERSION = '1.0.0' | {
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observational-astronomy, solar-system, comets, halleys-comet
Title: Details about the next big comet 2014 UN271? The announcent of the massive trans-Neptunian object 2014 UN271 to be a comet is rather new (June 22nd, 2021) and really exciting. That comet is rather huge (~100km diameter) and "falling toward the sun for a 'approach' outside the orbit of Saturn in early 2031." (citing the spaceweather.com-newsletter from today).
The name of the object suggests that it has been first observed in 2014, but do I understand it correctly that only now we learned that the object is outgasing therefore deserves the classification "comet"? | {
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php, library, plugin
switch($jns){
case 'FileUpload':
if($arr->getResourceTypeName() == "Images"){
if($arr->getClientPath() == "/slideshow/"){
$this->IUD_dbase("INSERT INTO ".$opt_cfg["main_table"]." (foto, keterangan, url_path, physical_path, create_time, create_by) VALUES ('".$fname."', '".$fname."', '".$Urlpath.$fname."', '".$Physicalpath.$fname."', '".date("Y-m-d H:i:s")."', '".$usr."')");
}
else{
$this->IUD_dbase("INSERT INTO ".$opt_cfg["other_table"]." (nama, keterangan, url_path, physical_path, create_time, create_by) VALUES ('".$fname."', '".$fname."', '".$Urlpath.$fname."', '".$Physicalpath.$fname."', '".date('Y-m-d H:i:s')."', '".$usr."')");
}
}
else{ | {
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observational-astronomy, amateur-observing, raw-data, data-pipeline
Security
Another stumbling stone is actually the security of these systems: all communication to spacecraft is made from separate networks which are not immediately accessible from the WWW. Setting up bridges poses a potential security risk - something which needs special care and active maintenance, more than a simple data dump needs where data are simply copied to from time to time - and thus in the end it needs money for people. That is done for the major missions but often that money and personel is not available for smaller projects and these tasks are done by people manually from time to time.
Data availabilty | {
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} |
quantum-information, quantum-computer, power
But think back to the example I gave earlier. The power for erasing the granite block came not from being parallel in space, but from being parallel in time. That is, each iteration of the eraser was "piled up" so that it took place during the same fragment of time, not just of space.
Time parallelism emerges only when you start considering the curious effect of entanglement, which plays havoc with ordinary concepts of time by providing effects that are "instantaneous" across distances in space. Relativity says very odd things about anything that works like that, since it makes space and time interchangeable.
So, the bottom line is this: | {
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visible-light, history, wave-particle-duality
Title: Newton's corpuscular theory Where did Newton get the idea that light had a particle nature and not a wave nature? At those times, AFAICT there were no phenomena that showed particle nature. But wave nature is much easier to detect. So, why didn't Newton change his theory to a wave theory? I recall something about "motion like Eels", but by Occam's razor, it makes more sense to just call it a wave and not a wavelike particle.
Was it just his arrogance? Or did he have some reason to stick to particle nature?
Edit: I actually wanted to ask why he didn't change his theory after wave nature was discovered. He instead complicated it with the Eels. I failed to see what supported the particle point. But it's answered now :D. From the paragraph Optics in the wiki article | {
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ros, ros-melodic, depth-image-proc
519], [440, 520], [440, 521], [440, 522], [440, 523], [440, 524], [440, 525], [440, 526], [440, 527], [441, 528], [441, 529], [441, 530], [441, 531], [441, 532], [441, 533], [441, 534], [441, 535], [441, 536], [441, 537], [441, 538], [442, 539]] | {
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proteins, protein-binding, synthetic-biology
To get the reaction to go to completion (>90% coupling), you'll need to wait ~12 times as long as the t1/2 (since every subsequent t1/2 doubles in a second-order reaction). This will, of course, depend on your concentrations. However, when using low concentrations (0.1 μM), complete coupling of SpyCatcher002 to SpyTag002 will take 1.5 hours, whereas SpyCatcher002 to SpyTag will take 7 hours at 25C. SpyCatcher002 to SpyTag1 will take 3x as long to go to completion; therefore, I'd recommend using at least 1-2 μM of what you want completely coupled with an equal or 2-4x excess amount of either Tag or Catcher and run the reaction overnight. Higher concentrations (>=10 μM of both Tag and Catcher) should go to completion in 30min-1hr. When performing coupling reactions for more than a few hours, I'd recommend you perform them at 4C. Loading 10 μL of 1-2 μM of your protein should allow you to see the band shift on an SDS-PAGE gel with Coomassie stain. | {
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Adding to the answer above, which correctly states that the logarithmic property $$\log (xy) = \log x + \log y$$ holds iff $$x,y > 0$$ :
If you are given the expression $$f(x) = \log\left( \frac{x+3}{x-3}\right)$$ then your argument is $$\frac{x+3}{x-3}$$ and you need to work with the domain restrictions applying to that. Furthermore, applying the property will only be viable for the corresponding parts of the domain.
This means, that $$f(x) = \log\left(\frac{x+3}{x-3}\right)$$ and $$g(x) = \log(x+3) - \log(x-3)$$ are two different functions.
• Thanks for your answer. It confirms what Lorenzo has written. – callculus Oct 30 '19 at 18:54 | {
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python, python-3.x, unit-testing, pandas
'SEQ_PERIODEND':
['2019-02-11', '2019-02-13',
'2019-02-14', '2019-02-14', '2019-02-15', '2019-02-16', '2019-02-17', '2019-02-18'],
'ID': [0, 1, 2, 3, 4, 5, 6, 7],
'NDAYS': [1, 2, 2, 5, 5, 5, 5, 5]
})
expected['SEQ_PERIODSTART'] = pd.to_datetime(expected['SEQ_PERIODSTART'])
expected['SEQ_PERIODEND'] = pd.to_datetime(expected['SEQ_PERIODEND'])
myops = Operations()
assert_frame_equal(expected, myops.disaggregate_ops_volume_date(input)) | {
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transform-listener, tf2, transform
Stripped your launch file down to just the static_transform_publisher
Opened up a console and started a roscore
Opened up another console and launched your file
Opened up two more consoles and echoed your /pose and /odom topics.
Opened up a final console and echoed the tf topic.
Did rosbag play bagfile.bag --clock -r 0.01.
I then waited for the pose message to get updated, paused the playback, and looked at your available transforms from the tf topic.
Here's what I found:
The time stamps between your pose, odom, and tf world->map transforms were all sufficiently small.
Your /pose topic has no frame_id. Not sure how you're getting your pose_world object above, but you might want to check that. | {
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java, object-oriented, linked-list, iterator
/**
* Inserts a non-sentinel node at front of the list.
*
* @param item
*/
public void insertFront(T item){
DListNode<T> node = new DListNode<>(item);
node.next = head.next;
node.prev = head;
node.next.prev = node;
head.next = node;
this.size++;
}
/**
* Remove first non-sentinel node from the list.
* Do not require size check before remove operation
*
*/
public void removeFront(){
head.next.next.prev = head;
head.next = head.next.next;
if(this.size() > 0){
this.size--;
}
}
public T get(int index) throws NoSuchElementException{
if (index > size()) throw new NoSuchElementException();
DListNode<T> node;
for (node = head; index-- > 0; node = node.next);
return node.item;
}
@Override
public Iterator<T> iterator() {
return new Itr();
} | {
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operators, entropy, quantum-entanglement, spin-chains
A small piece of supporting evidence (not near a proof) for the first conjecture is that it is easy to check that all product states $|p\rangle$ in the $S^z$-basis obey $\mathbb{S}[S^+|p\rangle] \leq \ln(2)$, as the resulting state's Schmidt decomposition has at most two states. Another small piece of supporting evidence, when I feed in random states for $|\psi\rangle$, the entanglement entropy decreases relative to the entropy of the random state. However, this is just supporting evidence that is far from a statement about all possible states in the Hilbert space. My conjectures in my question were incorrect. Since $S^+$ can destroy certain states, it's possible to begin with a low entanglement entropy state that gains a high entropy after being acted upon by $S^+$. | {
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electric-circuits, electrical-resistance, batteries
Title: Resistances in series or parallel
In the figure above,we have two cells $E_1$ and $E_2$ and $7$ resistances arranged as shown with $I_1$ current emitting from $E_1$ and $I_2$ emitting from $E_2$. Is it possible to find the equivalent resistance of such a circuit where there is more than one cell? If so,is my following understanding correct or flawed?
Since $I_1$ current is emitted from $E_1$ battery,this exact current should return to $E_1$. Hence $I_1$ current flows through $R_1,R_2,R_4$ and since the same current flows through them,therefore they are in series. With the same logic, $I_2$ current flows through $R_5,R_6,R_7$ and hence $R_5,R_6,R_7$ are in series. Only $I_3=I_1+I_2$ flows through $R_3$. Therefore,the equivalent resistance of the circuit is $(R_1+R_2+R_4) \parallel R_3 \parallel (R_5+R_6+R_7)$. | {
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homework-and-exercises, conservation-laws, conformal-field-theory
where the red line is $\Sigma$, the blue line is a deformation of it $\Sigma^\prime$ and the black lines are at infinity. Assuming our currents vanish at infinity, we can take
$$
Q(\Sigma) - Q(\Sigma^\prime) = \int_{\Sigma^\prime - \Sigma} dS_\mu \epsilon_\nu T^{\mu\nu}(x)
$$
and add the black lines to the domain of integration for free. The above then becomes the surface integral of something over a closed surface.
\begin{align}
Q(\Sigma) - Q(\Sigma^\prime) &= \oint dS_\mu \epsilon_\nu T^{\mu\nu} \\
&= \int dx \partial_\mu ( \epsilon_\nu T^{\mu\nu} ) \\
&= 0
\end{align} | {
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– Peter K.
Sep 14 at 17:08
• Thanks. It is clear now. Most papers use normalized score along the X axis. What type of normalization do they mean? How normalization is applied? On each vector separately or on both vectors simultaneously? If I have completely separable distributions before normalization, and the values of each vector are normalized to the range from zero to one, the two distribution will overlap, which is not correct. Sep 14 at 21:35 | {
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"url": "https://dsp.stackexchange.com/questions/78262/comparing-distribution-of-vectors-with-different-length"
} |
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Q&A
# Matrices with rotational symmetry
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−0
I've seen a claim without proof that the characteristic polynomials of matrices with rotational symmetry (i.e. $n \times n$ matrices $A$ with $A_{i,j} = A_{n+1-i,n+1-j}$) always factor into the product of the characteristic polynomials of smaller matrices which can be derived from blocks of the original matrix. Is there an elementary proof, and can the result be generalised?
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+3
−0 | {
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"url": "https://math.codidact.com/posts/286398"
} |
(In $\mathrm{Im}(F)$, note that all the positive odd numbers greater than or equal to 3 are generated by pairs of the form $(1,n)$ for $n\in\mathbb{N}$ since $1^2+2n=2n+1$, and all positive even numbers greater than or equal to 6 are generated by pairs of the form $(2,m)$ for $m\in\mathbb{N}$ since $2^2+2m = 2(m+2)$; this is why I can claim that $F(\mathbb{N}\times\mathbb{N}) = \mathbb{N}\backslash\{1,2,4\}$ for $0\notin\mathbb{N}$.)
I hope this makes sense!
Actually I had this question on a test and you're right x=(m,n) and we're told N does not include 0.
Anyways what does \ mean?
#### Chris L T521
##### Well-known member
Staff member
Actually I had this question on a test and you're right x=(m,n) and we're told N does not include 0.
Anyways what does \ mean?
Ah, that's one notation for set difference. I could have also written it as $\mathbb{N}-\{1,2,4\}$. | {
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"url": "https://mathhelpboards.com/threads/find-the-image-f-n-n-r-f-x-m-2-2n.7102/"
} |
c#, linq
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
//By containing string in field
case OperatorRef.LIKE:
{
MethodInfo contains = typeof(string).GetMethod("Contains");
var body = Expression.Call(Expression.Property(parameter, prop.Name), contains, Expression.Constant(fieldValue, prop.PropertyType));
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
// по умолчанию - "="
default:
{
var body = Expression.Equal(Expression.Property(parameter, prop.Name), Expression.Constant(fieldValue, prop.PropertyType));
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
}
} | {
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} |
json, delphi
function JsonEncode(const S: String): String;
var
X: Integer;
C: Char;
procedure Repl(const Val: String);
begin
Delete(Result, X, 1);
Insert(Val, Result, X);
end;
begin
Result:= StringReplace(S, '\', '\\', [rfReplaceAll]);
Result:= StringReplace(Result, '"', '\"', [rfReplaceAll]);
Result:= StringReplace(Result, '/', '\/', [rfReplaceAll]);
for X := Length(Result) downto 1 do begin
C:= Result[X];
if C = #10 then Repl('\'+#10);
if C = #13 then Repl('\'+#13);
end;
end;
{ TJsonBuilder }
constructor TJsonBuilder.Create(AOwner: TComponent);
begin
inherited;
FLines:= TStringList.Create;
FHierarchy:= 0;
FIndent:= 4;
FLineBreak:= True;
FNeedComma:= False;
end;
destructor TJsonBuilder.Destroy;
begin
FLines.Free;
inherited;
end;
procedure TJsonBuilder.Clear;
begin
FLines.Clear;
end;
procedure TJsonBuilder.SetIndent(const Value: Integer);
begin
FIndent := Value;
if FIndent < 0 then FIndent:= 0;
end; | {
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} |
c#, asp.net, asp.net-mvc, asp.net-mvc-5, razor
public ActionResult ConfirmPassword(string email = null)
{
ConfirmPasswordMV viewModel = new ConfirmPasswordMV
{
EmailID = email
};
return View(viewModel);
}
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult ConfirmPassword(ConfirmPasswordMV viewModel)
{
if (ModelState.IsValid)
{
if (viewModel.Password == viewModel.ConfirmPassword)
{
SecurityHelper.UpdatePassword(viewModel.EmailID, viewModel.Password);
TempData["Message"] = "Your password has been updated.";
return RedirectToAction(action, homeController);
}
ModelState.AddModelError("", "Password does not match.");
}
return View();
}
View Model
public class ConfirmPasswordMV
{
[Display(Name = "Enter your new password"), Required]
public string Password { get; set; }
[Display(Name = "Confirm Password"), Required]
public string ConfirmPassword { get; set; }
public string EmailID { get; set; }
} | {
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"openwebmath_score": null,
"tags": "c#, asp.net, asp.net-mvc, asp.net-mvc-5, razor",
"url": null
} |
quantum-field-theory, general-relativity, resource-recommendations, quantum-gravity, qft-in-curved-spacetime
For more mathematically oriented readers, I cannot help but recommend R. Brunetti, C. Dappiaggi, K. Fredenhagen & J. Yngvason's Advances in Algebraic Quantum Field Theory (2015) (with the collaboration of our very own V. Moretti!). In this book you will find a very thorough and up-to-date discussion of AQFT and its applications to, among others, quantum field theory in a curved background. Along the same lines, and as mentioned in the comments, Wald has dedicated several papers to the matter, so make sure to check them out.
Finally, the Wikipedia page on QFT in curved spacetime contains a list of many good references that you should check out too. Good luck! | {
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"url": null
} |
machine-learning, classification, clustering, statistics
If you don't want to feel like an impostor, I suggest the following: find some important algorithm still missing from the big toolkits such as sklearn, R, Weka, ELKI. Implement it, and contribute it to some open-source toolkit. Then you can call yourself an "sklearn contributor" in your resume, which puts you ahead of 90% of self-proclaimed data scientists. What could make you a more proven data scientist / machine learner than having written code used by other data scientists / machine learners? | {
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"openwebmath_score": null,
"tags": "machine-learning, classification, clustering, statistics",
"url": null
} |
c++, c++11, memory-management, pointers, coordinate-system
Title: NamedPoint class using unique_ptr for members After reading this old article from 2001 I have tried to implement the class from it using unique_pointer.
An author's claim is that C++ is not appropriate for large software projects because
My primary complaint against C++ is that the language is so complicated, and has enough booby-traps, that average and above-average programmers have a difficult time writing code without serious bugs.
This is the test he gave to candidates on his job interviews:
As part of my standard interview for C++ candidates I ask them to write me a small class with the intention of evaluating their command of the language. This also gives us a reasonable coding sample to discuss during the interview. I can ask about potential improvements, extensions and testing strategies.
The request of the author is: | {
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"tags": "c++, c++11, memory-management, pointers, coordinate-system",
"url": null
} |
in scientific notation. Scientific notation helps in easy reading, writing and calculating the small and very large numbers. But, such is not always the case. In this section, we will introduce the standard notation used to define sets, and give you a chance to practice writing sets in three ways, inequality notation, set-builder notation, and interval notation. Supports Many Features Such As Frames, Forms, Images Image Maps, Tables, Lists and More. 45 meter^2 kilograms / second^3. A positive exponent means the number is greater than one, and the decimal moves to the right to convert from scientific to standard notation. This worksheet requires students to use decimals in their scientific notation numbers. In scientific notation 183857. 314E+1 means 1. The spacing of abc notation will tend to mirror the grouping which would be used in standard notation. Hi guys, I am currently making a chord chart using standard notation. Our simple standard form converter is very helpful for students | {
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"lm_name": "Qwen/Qwen-72B",
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"openwebmath_score": 0.647797703742981,
"tags": null,
"url": "http://gyjw.chiesaevangelicapresbiteriana.it/standard-notation-converter.html"
} |
transition-metals, magnetism
Also, the teacher taught the idea paramagnetism and diamagnetism in the context of transition metals and said that transition metals show magnetic properties. Why don't other species show magnetic properties cause they can also have paired / unpaired electrons?
Do we determine paramagnetism / diamagnetism based on whether there is greater number of paired / unpaired electrons or if a transition metal ion has unpaired electrons, it must be paramagnetic? | {
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"tags": "transition-metals, magnetism",
"url": null
} |
reference-request, computability, machine-models
Title: Examples of reversible computations Irreversible computations can be intuitive. For example, it is easy to understand roles of AND, OR, NOT gates and design a system without any intermediate, compilable layer. The gates can be directly used as they conform to human's thinking.
I have read a paper where it was stated that it is obviously correct way to code irreversibly, and compile to reversible form (can't find the paper now).
I am wondering if there exists a reversible model, that is as easy to understand as AND, OR, NOT model. The model should be therefore "direct" use of reversibility. So no compilation. But also: no models of form: $f(a) \rightarrow (a,f(a))$ (ie. models created by taking irreversible function $f$ and making it reversible by keeping copy of its input). The paper you mention is probably one of Paul Vitányi's, possibly Time, Space, and Energy in Reversible Computing. | {
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"tags": "reference-request, computability, machine-models",
"url": null
} |
optics, reflection, diffraction
$$\phi(\rho, \theta) - x\,R\,\rho\,\cos\theta -y\,R\, \rho\,\sin\theta - \frac{\Delta z\, R^2}{4\,k} (2\rho^2 - 1) + \frac{\Delta z\, R^2}{4\,k}\quad\quad(10)$$
Here you see the two tilt and defocus Zernike functions $\rho\,\cos\theta$, $\rho\,\sin\theta$ and $2\rho^2 - 1$ and they correspond to sideways system misalignments (corresponding to tilts on your mirror, which I assume you have the freedom to impart for the sake of alignment) and small errors in the axial position of the output plane: again, I assume you have the freedom to impart small axial displacements to the mirror system in your alignment controls. The net aberration, after all these adjustments have been optimized, will be your mirror aberration $\phi(\rho, \theta)$ with the defocus and tilt Zernikes removed. Let $\tilde{\phi}(\rho, \theta)$ be the net aberration after tilt and defocus Zernikes have been removed. Then the Strehl ratio is: | {
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"tags": "optics, reflection, diffraction",
"url": null
} |
beamforming, polar
I also know that I can use the the ratio between the surface of the polar plot versus the whole 360° plane.
Thus, so long I only have two values in the array:
Beamwidth
Ratio polar plot vs plane
But are there other values that can describe the polar plot ?
And also, how can I have a value which describes second biggest lobe ? Some examples would be the null to null bandwidth(s) as well as the sidelobe levels of the first/second sidelobes.
Example vector of 5 numbers:
[mainlobe gain, first null location, 1st sidelobe gain, second null, 2nd sidelobe gain]
From this you could produce an estimate for the 3 dB points of each lobe using some "reasonable" formula, i.e. halfway between the peak and the null. | {
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"tags": "beamforming, polar",
"url": null
} |
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