text stringlengths 1 1.11k | source dict |
|---|---|
modulation, fsk
The quantity in square brackets has value $m_0$ if $a_i = 0$ and value $m_1$ if $a_i = 1$ and so during the time interval $[iT, (i+1)T)$, the signal
consists of either $m_0$ periods or $m_1$ periods of a sinusoid. At the
endpoints of the interval, the signal has value $0$. The signal thus has
the phase continuity that is desirable in an FSK signal as noted
by @JasonR in a comment.
If you are using some programming language to create an array of
$16$ gazillion points that you will then pass to a graphics package to display
as a graph of values of $x(t)$ as a function of $t$, then note that the
formulas used to create the first gazillion points will differ from the
formula used to create the next gazillion points etc.. The
formula needs to use $a_i$ to compute the values of the $i$-th
subset of gazillion points. If you want
to have a nice smooth graph of the sinusoids, it is necessary
to have $m_0$ and $m_1$ be onsiderably smaller than a gazillion
so that you get plenty of points | {
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ros, kinect, usb, rgbd, bandwidth
Originally posted by Philip with karma: 990 on 2013-04-30
This answer was ACCEPTED on the original site
Post score: 3 | {
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thermodynamics, atmospheric-science, ideal-gas, boltzmann-equation
If we recall the thought experiment that Maxwell and later Tsiolkovsky did with two gas columns, then we get a direct violation of the principle of universal applicability of the second law of thermodynamics (because different gases have different lapse rate), recognized among many physicists. Let the one who read this now live with this insane contradiction.
UPDATE
Updated experiment with: | {
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But that's clearly not the case as $$\mathbb{Z}/\mathbb{Z} = \{0\}$$ but $$\mathbb{Z}/\mathbb{2Z}=\{0,1\}$$ So where does one draw the line between two isomorphic groups? How "same" are two isomorphic groups? I'm very confused. | {
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If you want to be more sophisticated, once you have it for some infinite dimensional space you have it for Hilbert spaces by Dvoretzky's theorem. – Bill Johnson May 20 '14 at 14:23
Even more sophisticated is that every two dimensional real Banach space embeds isometrically into L$_1(0,1)$, so the inequality is true in all two dimensional Banach spaces. – Bill Johnson May 20 '14 at 14:38 | {
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"url": "http://mathoverflow.net/questions/167685/absolute-value-inequality-for-complex-numbers"
} |
mechanical-engineering, stresses, strength, bolting, fatigue
Title: Strength of bolts I was wondering if it'd be a good idea to attach a 10kg load to the end of a movable steel rod by fastening it with just one M5 bolt. Looking at Misumi's datasheet, M5 (Class 10.9) has an allowable load of 111kgf. 111kgf is 10x more than my requirement for static load. However, it's not quite clear if 111kgf is for both axial and radial directions. If the load was de/accelerated in any direction, would an M5 bolt be able to support that? For a 10kg load, does that mean if the de/acceleration of the load stayed below 10*9.8m/s^2 = 98m/s^2 (by F=ma), then a single M5 bolt would still be OK? Perhaps if the load was allowed to swing as well, the centrifugal force wouldn't be too far off?
Any guidance would be greatly appreciated.
EDIT1: Here's a diagram:
EDIT2: Here's a revised version: Simply put this is a textbook example of what not to do. | {
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quantum-mechanics, homework-and-exercises, lagrangian-formalism, quantum-optics
\tag{A-01.f\;$^{\boldsymbol{\prime\prime}}$}
\nonumber
\end{align}
\begin{equation}
\text{-----------------------------------------------------------}
\tag{A-01.f$\;^{\boldsymbol{\prime\prime}}$}
\end{equation}
Equations (A-02) and (A-03) are useful for the conversion of the Lagrangian from the form (3.1), see equation in question, to the form (10) and for the construction of this Lagrangian step by step from the equations of motion (08) :
\begin{align}
&\sum_{k}\dot{Q}_{k}^{2}=\boldsymbol{<}\mathbf{\dot{Q}}, \mathbf{\dot{Q}}\boldsymbol{>}=\left\Vert\mathbf{\dot{Q}}\right\Vert^{2}
\tag{A-02.a}\\
&\sum_{k}\omega_{k}^{2}(q)Q_{k}^{2}=\boldsymbol{<} \Omega^{2}\mathbf{Q}, \mathbf{Q}\boldsymbol{>}=\boldsymbol{<} \Omega\mathbf{Q},\Omega^{\rm{T}} \mathbf{Q}\boldsymbol{>}=\boldsymbol{<} \Omega\mathbf{Q},\Omega\mathbf{Q}\boldsymbol{>}=\left\Vert\Omega\mathbf{Q}\right\Vert^{2}
\tag{A-02.b}\\ | {
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general-relativity, gravity, orbital-motion, metric-tensor
and the Israel-Khan metric ("two black holes held in equilibrium by a strut"). Also of interest and related to the Israel-Khan metric :
"In a 1922 paper, Rudolf Bach and Hermann Weyl [3] discussed the superposition of two exterior Schwarzschild solutions in Weyl coordinates as a characteristic example for an equilibrium configuration consisting of two “sphere-like” bodies at rest. Bach noted that this static solution develops a singularity on the portion of the symmetry axis between the two bodies, which violates the elementary flatness on this interval. "
The Gott spacetime is constituted of two cosmic strings also, if that helps.
From "Exact Solutions of the Einstein Field Equations", by the way :
"In Einstein's theory, a two-body system in static equilibrium is impossible without such singularities - a very satisfactory feature of this non-linear theory." | {
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wavefunction, hilbert-space, vectors, linear-algebra, normalization
Title: Is a basis vector always unit-length in a wave function? I'm currently studying wave functions and I came across an assertion, that
$$\psi(x) = \left<x \middle| \psi \right>$$
is a projection of $\psi$ onto $x$. The vector projection being defined as
$$proj_x \psi = \frac{x \cdot \psi}{||x||} \frac{x}{||x||},$$
I don't see, how a wave-function, being just the scalar product, could be a projection, unless $x$ is always a unit-length vector.
Is it true? And if $x$ has always unit length, could you, please, explain why? The ket $|x\rangle$ is a little bit more complicated than that. Consider one Hilbert space $\mathcal{H}$ and one orthonormal basis $e_i\in \mathcal{H}$.
If $\{e_i : i \in I\}$ is an orthonormal basis then two different elements are orthogonal and each one has unit length. In other words:
$$\langle e_i,e_j\rangle = \delta_{ij}.$$ | {
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c++, algorithm, comparative-review, random
Critique request
Please tell me anything that comes to mind. However, I am most concerned with adherence to C++ programming idioms. Concept review
I had some controversial thoughts, but now it is all clear, after @Edward have provided the link to the std::discrete_distribution. So I'll mostly compare the code in the post with the distribution.
Multiple concerns
Current code does lifetime management and discrete distribution logic. I guess one could use something like this:
template <typename Container, typename PredefinedGenerator>
class discrete_select // ?
{
//other members
//insert check for difference type here
std::discrete_distribution<typename Container::const_iterator::difference_type> distribution;
public:
template <typename GeneratorArgs>
discrete_select(const Container& container,
std::initializer_list<double> weights,
GeneratorArgs&& ... args):
//initialize container and forward args to generator
{} | {
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electromagnetism, special-relativity, speed-of-light
$$\phi'(z',t')=k\gamma(z+vt)-\omega\gamma(t+\frac{vz}{c^2})$$
With:
$$ \gamma \equiv \frac 1 {\sqrt{1-\frac{v^2}{c^2}}}=\frac 1{\sqrt{(1-\frac v c)(1+\frac v c)}}$$
and
$$ \omega = kc$$
we get
$$\phi'(z',t') =k'z'-\omega't'=\phi(z,t)$$
where
$$k'=f_Dk$$
$$\omega'=f_D\omega$$
with:
$$ f_D = \sqrt{\frac{1-\frac v c}{1+\frac v c}}$$
is the well known Doppler factor.
So the phase of a plane wave is a Lorentz invariant: all reference frames agree on it, but the wavelength and frequency can be any non-zero number which depends entirely on the observer's reference frame.
(The field strength also transforms in manner that keeps the average number of photons invariant...should you go that route.). | {
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# Prime numbers using Sieve Algorithm in Python
May 19, 2017 12342
Sieve of Eratosthenes is used to get all prime number in a given range and is a very efficient algorithm. You can check more about sieve of Eratosthenes on Wikipedia. It follows the following steps to get all the prime numbers from up to n:
1. Make a list of all numbers from 2 to n.
[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ……., n]
2. Starting from 2, delete all of its multiples in the list, except itself.
[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,……., n]
3. Repeat the step 2 till square root of n.
For 3 – [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20……., n]
For 5 – [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20……., n]
Till sqrt(n)
The remaining list only contains prime numbers.
### Example of first 100 prime numbers | {
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ros, gazebo, rviz, gazebo7, ros-kinetic
Title: visualize points rviz python
Hello. I am trying to visualize a set o points in rviz. I have a node who subscribes to a topic to get some data and and publishes a Marker msg on a topic.
#!/usr/bin/env python
import rospy
from std_msgs.msg import String
import time
import numpy as np
import math
from time import sleep
from laser_line_extraction.msg import LineSegment
from laser_line_extraction.msg import LineSegmentList
from box_finder_var import *
from visualization_msgs.msg import Marker
from geometry_msgs.msg import Quaternion, Pose, Point, Vector3
from std_msgs.msg import Header, ColorRGBA
rospy.init_node('box_finder', anonymous=True)
marker_publisher = rospy.Publisher('box_visual', Marker, queue_size=100)
rospy.sleep(1)
def callback(data):
# calculate some points...
### Visualize the L-shape elements in rviz ###
show_points_in_rviz(marker_publisher) | {
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energy, astronomy, universe, observable-universe, data
Note: you can calculate numbers and get to answers below. Whether that makes sense as the source of energy for your theorem I won't speculate.
So if you want the total energy now (in the cosmological comoving time now) just calculate the critical energy density. We're pretty close to that, if you count the dark density and both normal and dark matter. And then multiply by the volume of the observable universe. Since you're probably going to be comoving that is your available total energy.
The numbers are easy enough. Critical density is about $10^{-26}$ kg/$m^3$. This includes the mass equiv. The radius is 46 Gly, and volume you can compute to be about $10^{80}$ $m^3$. The total mass is then about $10^{54}$ kg. Multiple by $c^2$ and you get about $10^{70}$ joules. See some of the numbers from which you can calculate and verify at https://en.wikipedia.org/wiki/Observable_universe | {
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ros, pose, transform
Originally posted by rbbg with karma: 1823 on 2016-11-30
This answer was ACCEPTED on the original site
Post score: 4
Original comments
Comment by mutu on 2016-12-01:
thank you! That solved my problem! | {
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symmetry, symmetry-breaking, crystals, phonons, goldstone-mode
Title: Why phonons are Goldstone modes? I read this in the lecture notes by David Tong:
"Gapless excitations often dominate the low-temperature behaviour of a system, where they are the only excitations that are not Boltzmann suppressed. In many systems, these gapless modes arise from the breaking of some symmetry. A particularly important example, that we will not discuss in these lectures, are phonons in a solid. These can be thought of as Goldstone bosons for broken translational symmetry." | {
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c++, multithreading, poco-libraries
public:
Balancer(MessageQueue& input_queue, MessageQueue& output_queue, WorkerPtr worker_prototype);
~Balancer();
void run();
void start();
void stop();
int threadPoolSize() const;
int runningWorker() const;
size_t workerSize() const;
int increasingCounter() const;
int decreasingCounter() const;
private:
std::unique_ptr<BalancerPimpl> pimpl_;
};
// Balancer.cpp
class Balancer::BalancerPimpl {
public:
BalancerPimpl(MessageQueue& input_queue, MessageQueue& output_queue, WorkerPtr worker_prototype);
void run();
void start();
void stop();
int threadPoolSize() const;
int runningWorker() const;
size_t workerSize() const;
int increasingCounter() const;
int decreasingCounter() const;
private:
using WorkerList = std::vector<WorkerPtr>;
static const int LIMIT_MULTIPLIKATOR;
static const int INCREASING_LIMIT;
static const int DECREASING_LIMIT;
static const int THREADPOOL_MIN_CAPACITY; | {
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ros
[ INFO] [1498670594.330961864]: Using planning request adapter 'Fix Start State Bounds'
[ INFO] [1498670594.330988864]: Using planning request adapter 'Fix Start State In Collision'
[ INFO] [1498670594.331017475]: Using planning request adapter 'Fix Start State Path Constraints'
[ INFO] [1498670594.388064804]: Fake controller 'fake_arm_controller' with joints [ joint_1 joint_2 joint_3 joint_4 joint_5 joint_6 ]
[ INFO] [1498670594.388886822]: Fake controller 'fake_tool_controller' with joints [ ]
[ INFO] [1498670594.389720156]: Returned 2 controllers in list
[ INFO] [1498670594.414805552]: Trajectory execution is managing controllers
Loading 'move_group/ApplyPlanningSceneService'...
Loading 'move_group/ClearOctomapService'...
Loading 'move_group/MoveGroupCartesianPathService'...
Loading 'move_group/MoveGroupExecuteTrajectoryAction'...
Loading 'move_group/MoveGroupGetPlanningSceneService'...
Loading 'move_group/MoveGroupKinematicsService'...
Loading 'move_group/MoveGroupMoveAction'... | {
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turing-machines, semi-decidability
Does this make any sense?
Also, since I need to prove/disprove $A$'s semi-decidability, I conclude that $A$ is not decidable (Rice's theorem), is that correct? What you have to do is systematic search for a string $x$ such that $f_w(x) = |x|$ or in other words $M_w(x) = |x|$. Given $w$ your TM $M$ should try ALL input strings $x$, not just to simulate $M_w$ on a single $x$.
If you wait $M_w(x)$ until it halts then you ($M$) may stuck in case $M_w$ does not halt on $x$. So, that option is not possible. | {
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following formulas are used for circle calculations. Utility to calculate diameter, radius, circumference and area of a circle. Example 2 Michael has a circular park of diameter 21 feet in front of his house. See radius of a circle. Know the radius? An online circumference calculator that allows you to find circumference, radius, diameter, area, sphere surface area, and sphere volume of a circle. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to a line segment. So if you know the circumference, you can find the radius by dividing the circumference by both pi and 2. Click Create Assignment to assign this modality to your LMS. Example 1. Need a custom math course? The distance must be measured along a straight line, similar to what you would get if you used a ruler, connected 2 dots together, and then measured the distance between both dots. Similarly, if you enter the area, the radius needed to get that area will be | {
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thermodynamics
The inequality applies if the condition of reversibility does not hold during the path of the process: the more the process deviates from equilibrium, the bigger the inequality. This is the second law.
Only entropy has this unique dependence on reversibility. The integral of $dV$ (or any other state function) over any closed path is exactly zero regardless of whether the process was conducted reversibly or not. But entropy is a special property that is associated with all inequalities that appear in thermodynamics. | {
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electromagnetism, gauss-law, spacetime-dimensions, coulombs-law
But there are solid theoretical reasons for choosing to generalize E&M to different numbers of dimensions by choosing to hold Maxwell's equations "fixed" across dimensions, rather than, say, Coulomb's law, the Biot-Savart law, and the Lorentz force law. For one thing, it's hard to fit magnetism into other numbers of dimensions while keeping it as a vector field - the defining equations of 3D magnetism, the Lorentz force law and the Biot-Savart law, both involve cross products of vectors, and cross products can only be formulated in three dimensions (and also seven, but that's a weird technicality and the 7D cross product isn't as mathematically nice as the 3D one). | {
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r, text-processing, merge
This could be achieved in awk, but I would really like an R solution.
For the logic, here is the awk way:
sort test1 | awk '{if(a!=$1) {a=$1; printf "\n%s%s",$0,FS} else {a=$1;$1="";printf $0 }} END {printf "\n" }' > test2 For a data.frame named foo:
sink('some_output_file.txt')
uvals = unique(foo[,1])
for(uIDX in c(1:length(uvals))) {
gname = uvals[uIDX]
IDX = which(foo[,1] == gname)
cat(sprintf("%s\t%s\n", gname, paste0(foo[IDX,2], collapse="\t")))
}
sink() | {
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general-relativity, acceleration, vectors
To see this, recall the definition of the four acceleration: $$A^\mu = \frac{d}{d\tau}U^\mu + \Gamma^{\mu}{}_{\nu \lambda} U^\nu U^\lambda$$ so for an object at rest on the surface we have $U=(1,0,0,0)$ and thus only the $\Gamma^{\mu}{}_{tt}$ Christoffel symbols are relevant.
In Schwarzschild coordinates the only tt Christoffel symbol (p. 18) is $$\Gamma^r {}_{tt}=\frac{c^2 R(r-R)}{2 r^3}$$ so the four acceleration is purely in the r direction | {
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"tags": "general-relativity, acceleration, vectors",
"url": null
} |
c++, c++11
int main() {
constexpr double limit{2};
constexpr double epsilon{0.5};
constexpr char ops[]{'+','-','*','/','?'};
for (const char op : ops) {
for (auto first{-limit}; first < limit; first += epsilon) {
for (auto second{-limit}; second < limit; second += epsilon) {
auto result{applyOperation(first, second, op)};
if (result) {
std::cout << first << " " << op << " " << second << " is " << result.value() << '\n';
} else {
std::cout << "Invalid operator '" << op << "'\n";
}
}
}
}
} | {
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} |
# Dodecahedral rolling distance
Let a dodecahedron sit on the plane, with one face's vertices on an origin-centered unit circle. Fix the orientation so that the edge whose indices are $(1,2)$ is horizontal. For any $p \in \mathbb{R}^2$, define the dodecahedral distance $dd(p)$ from $o=(0,0)$ to $p$ to be the fewest number of edge-rolls that will result in a face of the dodecahedron landing on top of $p$. Equivalently, imagine reflecting a regular pentagon over edges, as illustrated below: It takes $4$ rolls/reflections to cover $p=(5,\pi)$:
$p=(5,\pi)$, $dd(p)=4$, $s=(3,1,4,2)$.
My main question is:
Q. Given $p$, how can one calculate $dd(p)$?
Greedily choosing, at each step, the roll that is best aligned with the vector $p-o$ does not always succeed. | {
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"tags": null,
"url": "https://mathoverflow.net/questions/288550/dodecahedral-rolling-distance/288566"
} |
c#, html, mvc, asp.net, authorization
Here's my RoleCreateViewModel
/// <summary>
/// Views\Admin\RoleCreate.cshtml
/// </summary>
public class RoleCreateViewModel
{
[Required]
[Display(Name = "Name", ResourceType = typeof(Resources))]
public string Name { get; set; }
}
and RoleCreate actions
//
// GET: /Admin/RoleCreate
[HttpGet]
[Authorize(Roles = "Admin")]
public ActionResult RoleCreate()
{
return View();
}
//
// POST: /Admin/RoleCreate
[HttpPost]
[Authorize(Roles = "Admin")]
public ActionResult RoleCreate(RoleCreateViewModel vm)
{
context.Roles.Add(new IdentityRole()
{
Name = vm.Name
});
context.SaveChanges();
ViewBag.ResultMessage = Resources.RoleCreatedSuccessfully;
return RedirectToAction("RoleIndex");
} | {
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"tags": "c#, html, mvc, asp.net, authorization",
"url": null
} |
Let $y = \arctan(x)$, and try to find $\frac{dy}{dx}$. We have $$y = \arctan(x)$$ $$\tan(y) = \tan(\arctan(x))$$
We'd like to simplify the right-hand side. The definition of $\arctan(x)$ is: $$\arctan(x) = \textrm{the angle between }-\frac{\pi}{2} \textrm{ and } \frac{\pi}{2}\textrm{ whose tangent is } x.$$ So whatever $\arctan(x)$ is, its tangent must be $x$. That is, $$\tan(\arctan(x)) = x.$$ So we have $$\tan(y) = x$$ Now differentiate both sides with respect to $x$ (this is called implicit differentiation): $$\frac{d}{dx} \tan(y) = \frac{d}{dx} x$$ $$\sec^2(y) \frac{dy}{dx} = 1$$ $$\frac{dy}{dx} = \cos^2(y)$$ $$\frac{d}{dx}\arctan(x) = \cos^2(\arctan(x))$$ But it turns out that $\cos^2(\arctan(x)) = \frac{1}{{1+x^2}}$. To see this, you can draw a right triangle with vertices at $(0,0), (1, 0)$, and $(1, x)$. The angle at the origin is $\arctan(x)$, and you can easily compute its cosine. (Try it!) | {
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"openwebmath_score": 0.9975106120109558,
"tags": null,
"url": "https://math.stackexchange.com/questions/29649/why-is-arctanx-x-x3-3x5-5-x7-7-dots"
} |
python, python-3.x, strings, iteration, generator
Title: Generating sequential alphanumeric values that match a certain pattern I'm working on generating large volumes of test data for some performance testing. Part of this is going to involve generating a lot of values that represent an "MBI", which is a certain kind of alpha-numeric identifier.
This identifier has the following rules:
Is alpha-numeric (uppercase only letters)
Excludes letters that are commonly confused for numbers or other letters (SLOIBZ)
Is 11 digits long
Has specific rules on which values can go in which digit
The first digit can be a number 1-9
The second, fifth, eighth, and ninth digits can be any upper case letter besides SLOIBZ; I don't actually validate the upper-case requirement, and I just call mbi.upper() as needed.
The fourth, seventh, tenth, and eleventh digits can be any number 0-9
The remaining digits (third and sixth) can be any of the valid letters or numbers (including 0) | {
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"tags": "python, python-3.x, strings, iteration, generator",
"url": null
} |
# Why is derivative a two-sided limit?
Well, I haven't thought that I'll ask these kind of questions but well, really I do not really understand that.
Suppose we are making some secant lines in order to get the average rate of change and therefore we have points $x$ and $a$ - points of intersection with the function. Point $x$ is the point where we want to find an instantaneous rate of change. So what we are doing is making the second point closer and closer to $x$ and here is the problem. | {
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"lm_q1q2_score": 0.8042506673194618,
"lm_q2_score": 0.8267117940706734,
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"openwebmath_score": 0.9410523176193237,
"tags": null,
"url": "https://math.stackexchange.com/questions/2782768/why-is-derivative-a-two-sided-limit/2782790"
} |
##### Well-known member
Re: inequality
I think you've assumed tacitly $k^3\geq2^{k+1}$ for $k\geq2$, but it's only true for $k=2,3,4,5,6,7,8,9$!
መለሰ
I did not assum tacitly $k^3\geq2^{k+1}$
I only constructed a geometric series with ratio 1/2 (1 not included) and
compare terms by terms
ex:1=1 , 1/8 =1/8
1/27 <1/16
1/64<1/32
1/125<1/64
--------
and the infinite geometric series (first term=1/8 , and ratio =1/2) sums up to 1/4
so S<1+1/4=5/4
Last edited:
#### Opalg
##### MHB Oldtimer
Staff member
Re: inequality
I did not assum tacitly $k^3\geq2^{k+1}$
I only constructed a geometric series with ratio 1/2 (1 not included) and
compare terms by terms
ex:1=1 , 1/8 =1/8
1/27 <1/16
1/64<1/32
1/125<1/64
1/216 < 1/128
1/343 < 1/256
1/512 = 1/512 Things are not looking so good already!
1/729 < 1/1024 NOT TRUE!!
--------
and the infinite geometric series (first term=1/8 , and ratio =1/2) sums up to 1/4 | {
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"openwebmath_score": 0.9977326989173889,
"tags": null,
"url": "https://mathhelpboards.com/threads/inequality.4008/"
} |
programming-languages, polymorphisms
Strachey distinguished between parametric polymorphism, where there is no information about the actual type and any type can be passed as an argument, and ad hoc where an arbitrary set of types has been nominated as acceptable. Subtyping is not parametric polymorphism because a specific type (the superclass) is known. So the question is, is it ad-hoc?
The choice of the term ad hoc emphasises that there need be no relationship between the different types in a given abstraction; the only unifying factor is the existence of concrete implementations that make them part of the set. Operator overloading and Haskell's type classes fit that criteria. | {
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"tags": "programming-languages, polymorphisms",
"url": null
} |
quantum-mechanics, operators
fulfill $\hat{Q}_i(x,p) = Q_i(\hat{x},\hat{p})$, even after resolving ordering ambiguities in the second expression, so we do not preserve the "freedom of coordinate choice" in the course of quantization. | {
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"tags": "quantum-mechanics, operators",
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} |
acid-base, buffer
Title: Finding final pH of the buffer solution without applying Henderson equation
A is beaker with $\pu{0.1 M}$ $\pu{25 cm^3}$ solution of $\ce{NH3}.$ B is beaker with $\pu{0.1 M}$ $\pu{5 cm^3}$ $\ce{HCl}.$ Now the solution of A and B is mixed. What will be the final $\mathrm{pH}$ of the mixture? $K_\mathrm{b} = \pu{3.3E-5}.$ | {
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"openwebmath_score": null,
"tags": "acid-base, buffer",
"url": null
} |
c#, singleton
return new Cart();
}
set {
HttpContext.Current.Session["Cart"] = value;
}
}
private SessionFactory(String username, long cartId)
{
this._UserName = username;
this._CartId = cartId;
// build Session objects here
}
public long CartId{
get {
return _CartId;
}
}
public static SessionFactory Instance {
get {
if (instance == null) {
throw new Exception("Session was not created");
}
return instance;
}
}
public static void Create(String userName, long cartId) {
if (instance != null) {
throw new Exception("Session Instance already created.");
} | {
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"openwebmath_score": null,
"tags": "c#, singleton",
"url": null
} |
c++, c++11, database
/* Print these specific indexes */
void pretty_print(std::ostream &stream, std::vector<size_t> idxs) const {
if (idxs.size() == 0) {
return;
}
/* find the max length of each field so I can pretty each column with a fixed width */
size_t last_w = max_width_idx(idxs, [](const Contact &c) { return c.last_name; });
size_t first_w = max_width_idx(idxs, [](const Contact &c) { return c.first_name; });
size_t middle_w = max_width_idx(idxs, [](const Contact &c) { return c.middle_name; });
size_t phone_w = max_width_idx(idxs, [](const Contact &c) { return c.phone_number; });
size_t address_w = max_width_idx(idxs, [](const Contact &c) { return c.address; });
last_w = std::max(last_w, (size_t)5) + 2;
first_w = std::max(first_w, (size_t)5) + 2;
middle_w = std::max(middle_w, (size_t)6);
address_w = std::max(address_w, (size_t)7);
phone_w = std::max(phone_w, (size_t)5); | {
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"tags": "c++, c++11, database",
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} |
ros, nav-msgs
Originally posted by ljaniec on ROS Answers with karma: 3064 on 2022-02-14
Post score: 0
I'm not exactly sure why you're seeing that. I might recommend try a new terminal, sourcing /opt/ros/galactic/setup.bash and rebuilding after deleting your install / build spaces in case there's some odd caching going on.
I just cloned the galactic branch in my /tmp directory and confirmed that nav2_util is building fine and the binaries are also tuning over in CI.
Originally posted by stevemacenski with karma: 8272 on 2022-02-14
This answer was ACCEPTED on the original site
Post score: 1
Original comments
Comment by ljaniec on 2022-02-14:
It must have been this odd thing with cache because I can't reproduce it now with rebuilding everything again (even after removing ros-galactic-nav-2d-msgs, ros-galactic-nav-msgs) and sourcing everything by hand in known sequence. At least Google will lead people with the same (rare?) problem to this question. | {
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} |
php, beginner, object-oriented, classes, database
For further ways to Type-hint for PHP in Netbeans check out this post I wrote a while ago.
Is this the correct way of using OOP and classes (mainly the DB connection)?
I would pass the PDO object to the user class in the constructor instead of using global.
It looks cleaner, and it would make writing unit tests a lot easier as well (you could pass a connection to a test database without changing the code or mock the PDO class). It also has the neat side-effect that you are able to define the type and thus enable auto complete.
Misc
classes should start with an upper-case letter (User).
is_int($ID) == TRUE can be written as is_int($ID).
I find it a bit odd that you return false for wrong parameters, but not for an unsuccessful delete in deleteUser.
checking empty has the effect of not deleting the user with id 0. Is this on purpose? If yes, I would make this explicit ($id != 0), if no, just remove it, it doesn't do anything else that is_int wouldn't cover. | {
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thermodynamics, electromagnetic-radiation, power
Later:
Prompted by Anna I have done the experiment. I used two identical coffee mugs containing 400g of water each. I first heated just one mug and measured the temperature rise every ten seconds from about 10C up to about 25C - I didn't want to go higher because you have to start worrying about heat loss to the mug and air.
I then replaced the water and heated the two mugs together, spaced as widely apart as possible, and again graphed the temperature as a function of time again up to about 25C. The results? Well my oven is rated at 600W and with one mug I measured the rate of temperature rise to be 481W (plus or minus a few percent). With two mugs the rate of temperature rise was 530W.
Now I'll just post the results up to the arxiv :-) | {
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Assume without loss of generality that the two squares to be removed are in different rows. (Otherwise turn the board 90°).
First cover the board in horizontal dominoes, and connect the two squares by a zig-zag line like this:
which follows the rule that if the line goes through one end of a domino, it immediately connects to another end. (The requirement that the two squares have different colors ensure that this will be true of the end of the path if only we start out in the right direction for this to hold at the beginning). Now you can flip dominoes along the zig-zag line to produce a covering that avoids the two squares.
With a bit of (easy) special-casing for the same-row case, this strategy can be extended to any size board as long as one of the side lengths is even and the other is $\ge 2$. | {
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"url": "https://math.stackexchange.com/questions/1969751/is-it-possible-to-cover-a-8-times8-board-with-2-times-1-pieces"
} |
ai-design, game-ai
var: teamWeakAgainst: []
var: teamStrongAgainst: []
var: selectedTeam: []
while (size(selectedTeam) < 6)
goodMatches <- allPokemon.max(p -> size(p.strongAgainst.intersect(teamWeakAgainst)))
goodMatches <- goodMatches.min(p -> size(p.weakAgainst))
goodMatches <- goodMatches.max(p -> size(p.strongAgainst))
selectedPokemon <- goodMatches.random()
teamWeakAgainst -= selectedPokemon.strongAgainst
teamWeakAgainst += selectedPokemon.weakAgainst # not counting previously selected pokemon because the current one adds another "weakness", even if it was already accounted for
selectedTeam += selectedPokemon
output: selectedTeam | {
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"openwebmath_score": null,
"tags": "ai-design, game-ai",
"url": null
} |
biochemistry, microbiology, virology, coronavirus
Fomite transmission (contact w/ inanimate or nonpathogenic object surface transmission exclusive of food components) reduction via biocidal agents such as 0.1%-0.5% NaOCl aka 1000-5000 ppm. “...Human coronaviruses on inanimate
surfaces can be effectively inactivated by surface disinfection procedures with 62-71% ethanol, 0.5% hydrogen peroxide or 0.1% sodium hypochlorite within 1 minute.” from pre-print https://doi.org/10.1016/j.jhin.2020.01.022
Edit: The question is really about disinfecting for SARS-CoV-2, the mRNA virus which causes COVID-19 in humans.
The edit is to:
1) Clarify the actual question, which deals w/ microbiology relating to SARS-CoV-2, not a medical disease condition COVID-19;
2) Acknowledge that the press has incorrectly used the two different terms interchangeably creating public confusion & explain why many professionals are responding in forums around the world trying to clear up that confusion by providing accurate information; | {
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"tags": "biochemistry, microbiology, virology, coronavirus",
"url": null
} |
c++
Title: Find the oldest person by Lithuanian National Identification Number I made a program which parses the NIDs from kodai.txt file and calculates the oldest woman and man and outputs their DOB.
#include <iostream>
#include <fstream>
#include "math.h"
using namespace std;
enum Genders {
Man, Woman
};
struct Person {
Genders gender;
int dobYear;
int dobMonth;
int dobDay;
long code;
};
Person parsePerson(long kodas) {
Person person;
kodas = kodas / 10000;
int firstNumber = kodas / 1000000; | {
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"openwebmath_score": null,
"tags": "c++",
"url": null
} |
java, performance
String newText = "";
GroupSection retrievedSection = this.groupSectionService.getGroupSectionById(msectionId);
GroupCanvas ownedCanvas = this.groupCanvasService.getCanvasById(retrievedSection.getCurrentCanvasId());
GroupAccount ownedAccount = this.groupAccountService.getGroupById(ownedCanvas.getGroupAccountId());
GroupNotes databaseNoteObject = this.groupNotesDAO.getGroupNoteById(noteObjectFromUser.getMnoticesid());
GroupMembers loggedInMember = this.groupMembersService.returnMembersMatchingUsernameAccountId(person.getUsername(),
ownedAccount.getGroupId());
String oldText = databaseNoteObject.getMnotetext();
String oldTag = databaseNoteObject.getMnotetag();
databaseNoteObject.setMnotetext(databaseNoteObject.getMnotetext().replaceAll("\\s*id=\"cke[^\">]*\"",
""));
if ((loggedInMember.isAccesslevel())) { | {
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"lm_q2_score": null,
"openwebmath_perplexity": null,
"openwebmath_score": null,
"tags": "java, performance",
"url": null
} |
python, datetime, python-2.x, json, console
Using contexts
You open files in different places in your code and then you need to close them. Congratulations for thinking about closing them, this is a usual error. Fortunately, Python provides you a nice keyword so that you don't need to do the closing "manually" : the with keyword. I suggest you read about it as it is really interesting.
There is a lot more to say but this should give enough some food for thought. | {
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} |
neural-network, gradient-descent, backpropagation
In case of neural networks, we get back a layer of activations (outputs), and we have the expected outputs with matching shape, so we're getting the costs, by subtracting the expected output, with our actual output, and we're propagating this back with the chain rule. But this way we have to compare our costs with the activations of the neurons, which are unique, and dependent on the inputs. So even if we would take a bunch of inputs, get their costs, and average the costs, how could we decide which neuron activation layer should it be compared to? After weeks trying to get into the very depth of the question as someone who's not from a maths background, neither data science, I figured out how it works internally.
This is one, raw way to make it work, and my implementation, haven't seen it anywhere implemented like this, I'm pretty sure there are more modern ways to do it, so if you want, use it with caution.
Here's the code: | {
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c#, reflection
I believed that one huge advantage he might have is that he's emitting IL to build a delegate while I was using expressions and so I spent the time figuring out how to emit the IL I needed. The problem? Once finished I only gained maybe 5 ns, he was beating me by at least 20 times that amount! This is when I learned that the slowest part of the entire process is not executing the delegate but extracting it from the cache.
I was using ImmutableDictionary<,> and wow is it slow! Really slow, even calling TryGetValue is at least 3 times slower than the normal Dictionary<,> class. Don't just take my word for it either as others have documented the same experience and I suppose it's not surprising giving the promises that the class has to fulfill. What surprised me more however is that TryGetValue itself is quite slow when compared to the pattern of try { return dictionary[key]; } catch (KeyNotFoundException e) { ... }. | {
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quantum-mechanics, heisenberg-uncertainty-principle, measurement-problem
Stating this in easier-to-understand terms, the proof of Heisenberg's uncertainty principle assumes that the disturbance in the measured system is independent of the state the system is in. If you set up an experiment where the disturbance depends on the state of the measured system (it isn't immediately clear how you can do this), then for some states the amount of disturbance can be lower than what Heisenberg's uncertainty principle says. Ozawa also gives a modified formula for the uncertainty principle which takes this into account.
The experiment described by the article is a demonstration of this. The experimental disturbance is shown to be lower than what Heisenberg's uncertainty formula yields, but is still larger than that given by Ozawa's modified formula. This experiment undoubtedly wasn't easy to do, but it agrees with the standard predictions of quantum mechanics. | {
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The accuracy increases if the expansion point is a pole or zero and OrderMode is set to relative.
### Plot Accuracy of Padé Approximant
Plot the difference between exp(x) and its Padé approximants of orders [1 1] through [4 4]. Use axis to focus on the region of interest. The plot shows that accuracy increases with increasing order of the Padé approximant.
syms x
expr = exp(x);
hold on
grid on
for i = 1:4
end
axis([-4 4 -4 4])
legend('Order [1,1]','Order [2,2]','Order [3,3]','Order [4,4]',...
'Location','Best')
title('Difference Between exp(x) and its Pade Approximant')
ylabel('Error')
## Input Arguments
collapse all
Input to approximate, specified as a symbolic number, variable, vector, matrix, multidimensional array, function, or expression.
Expansion variable, specified as a symbolic variable. If you do not specify var, then pade uses the default variable determined by symvar(f,1). | {
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c, io, localization
break;
case 'n':
break;
default:
printf("A resposta não é valida. digite s-sim, n-não. \n");
grauRisco();
break;
}
return ;
} setlocale() expects language tags
You call setlocale(LC_ALL, "Portuguese"), but unfortunately the system does not expect the English name for a language, but rather a so-called language tag, a combination of ISO country and language codes. For example, if you wanted Portuguese spoken in Portugal, it would be pt_PT, but if you wanted Portuguese as spoken in Brazil, it would be pt_BR.
setlocale() doesn't change how keyboard input works | {
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"url": null
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bioinformatics, database, gene
Title: What does curated gene mean? I see in databases "curated" or "not curated" for genes. What does that mean? "Curated" is mostly synonymous with "manually curated", which means that these genes have been experimentally validated. Most non-curated genes are just predicted by a software. | {
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Furthermore, the 2-(-1) band matrix is not symmetric positive-definite, so the Gauss-Seidel is not known to be convergent based on that criterium.
However, I believe the iterative matrix of the 2-(-1) band matrix ($D^{-1}R$) has a spectral radius smaller than 1, making the Jacobi method convergent.
Yes,I also noticed that the iterative matrix of the 2-(-1) band matrix ($D^{-1}R$) has a spectral radius smaller than 1 for all the dimensions I checked,but I get as result that the methods do not converge..Why does this happen??
#### Klaas van Aarsen
##### MHB Seeker
Staff member
Also,is the Hilbert matrix strictly dominant,so that the Jacobi methodi would converge,but it doesn't because of the fact that the matrix is ill-conditioned??Or isn't it strictly dominant?
The Hilbert matrix is not strictly diagonally dominant.
You may want to look up the definition if you want to use it in your work. | {
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terminology, programming-languages, semantics
Title: What is pass-by-value-result and its advantage and disadvantage? I have searched on Google, but I can't quite understand what is pass-by-value-result. What is the advantage and disadvantage of using pass-by-value-result?
If I have a program code like this, what will be the result when parameters are passed by value-result?
#include <stdio.h>
int a=2;
int b=1;
void fun(int x, int y) {
b=x+y;
x=a+y;
y=b+x;
} | {
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between 2 TVs. 1 Attachment. Word allows you to do much more than simply insert or place graphics. If all 6 letters were distinct, we would have 6! different rearrangements. This is a simple Sales Contract template directed between between two parties that covers a variety of agreements for the seller and buyer to comply with in order to proceed. This is a small kindness that deserves many thanks. com, the world's most trusted free thesaurus. Open Microsoft Word. In how many ways can Find the number of ways 10 statues can be displayed if each number of statues is. 3 million penalties in 2002 to 37. Vedic clan’s gods, Rishis and priest Brahmans all are wine drinkers and meat. In counting arrangements of objects that contain look-alikes, the normal factorial formula must be modified to find the number of truly different arrangements. First, multiply by 100, then subtract or add the other number in the problem. Now, we are left with the arrangement of the remaining, 10 − 1 = 9 beads. If | {
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"url": "http://xrayworks.de/find-the-number-of-distinguishable-arrangements-of-the-letters-of-the-word-billion.html"
} |
evolution, flowers
The reality is that specific behaviours are affected by evolution of other behaviours and other traits as well as an by our environment (incl. social environment). It will be particularly difficult to hypothesize as for the different selection pressures that may have existed on a specific behaviour especially in animals with such high cognition as humans. Maybe we like flowers because we like colour contrast and maybe we like colour contrast because face with stronger colour contrast is more attractive because it is a sign of health. Maybe we like sunset because we like flowers. Maybe we like colour contrast because we like fresh fruits. Maybe, we like complex design because it makes us think about the possible complexity of shapes. Maybe we like complex shapes because we like to explore. Maybe we like simple design because we like clear skins. Maybe we like flowers because of the diversity of shapes. Maybe we like flowers because they are a sign of the end of the cold winter. Maybe we | {
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infection
Title: Why isn't direct diagnosis of infectious disease through microscopes a common thing? I'm not sure if I am being accurate about this but from what I know about diagnostics (watching House MD etc), if a doctor has a suspicion of a pathogenic infection then he/she usually prescribes corresponding medication without doing some kind of a confirmatory test. But isn't it possible to just have a look at the blood sample under a microscope and then confirm it? I guess it can't be done for viruses because they need an electron microscope to resolve them apart but I guess normal bacterias can be identified using more commonly available microscopes. The problem with this is that A) the infection may be local, and very few if any bacterial cells may be in circulation, and B) even if the infection is systemic, there could be as few as a couple of bacterium per million red and white blood cells, making visual confirmation impossible. More often, if the attending physician feels the need for a | {
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beginner, html, html5
<footer>
<p>This is my fotter</p>
</footer>
</div> <!-- end #container -->
</body>
</html> About your use of sections
The body sectioning root is fine: it has a header containing the site-wide heading (h1) and the site-wite navigation (nav) (good!), a footer, and several sections representing the document’s main content. If you want, you could use the main element as a container for the section(s) that represent the main content.
Your first section, the article (#about-me), contains a section and an aside. Without knowing what content these have, it can’t be said if it’s correct or not. To make sure: | {
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string-theory, supersymmetry, spacetime-dimensions, quantum-anomalies, tachyon
Now, for the superstring, the local symmetries on the world sheet are enhanced from the ordinary conformal group to the $N=1$ superconformal group. One needs to add the $\beta\gamma$ (bosonic) ghosts for the new (fermionic) generators. Their dimension is $J=3/2$, different from $J=2$ of $bc$ by $1/2$, as usual for the spin difference of things related by supersymmetry. You see that $k=2J-1=2$ and $3k^2-1=12-1=11$. Now, the central charge of $\beta\gamma$ is $3k^2-1$ and not $1-3k^2$, the sign is the opposite one, because they are bosons. | {
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particle-physics, atomic-physics, electronics
When many many atoms come together to form a solid, much the same thing happens. Except that the energy level splits not into two levels, but $N$ levels, where $N$ is the order of Avogadro's Number. Instead of two levels separated by a gap, one ends up with a smeared out band of levels. | {
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thermodynamics, water, heat-conduction
of course, you're assuming that the water is kept exactly at $100°C$ with just enough heat to maintain its temperature but no more to trigger boiling but even then water wins in passing the heat by virtue of being a liquid. Barring the odd case of superheated, high-pressure steam, you're not conducting heat well enough. | {
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There are a total of $$52 \choose 5$$ ways to draw hands of 5 cards, so the answer is:
$$\frac{2 * 4 * 4 * {46 \choose 3} + 4 * 4 * 4 * {49 \choose 2}}{52 \choose 5} = 0.215$$
...which is wrong. The answer is $$0.1765$$, which was obtained by taking $$1 - P(A\cup B)$$, where $$A$$ is no aces and $$B$$ is no king or queen. Where did I go wrong? | {
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"url": "https://math.stackexchange.com/questions/3115836/probability-of-ace-and-king-or-queen-in-a-5-card-draw"
} |
research-level, differential-geometry, gauge-theory, singularities, geodesics
Well, what an ambitious project. But in any case I have made some progress for the n-dimensional case with n-vertices where the space is "regular" and I haven't introduced advanced mathematics yet. I'm mostly playing around in configuration space for vertices in euclidean space or something similar.
I have defined a functional in configuration space that gives the length of all possible paths in configuration space between two distinct sets of vertices in $\mathbb{R^n}$ as follows:
$$T = \int\limits_{\lambda_{1}}^{\lambda_{2}}
\sqrt{\sum_{I=1}^{n} \sum_{i=1}^{d}
\left(\frac{d}{d\lambda}\left(\sum_{j=1}^{d} s(\lambda)R_{j}^{i}(\lambda)(q_{I}^{j}(\lambda) + a^{j}(\lambda))\right)\right)^2} d\lambda$$ | {
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ros, opencv, vslam, opencv2, opencv2.2
// draw the left points corresponding epipolar lines in left image
std::vector<cv::Vec3f> linesRight;
cv::computeCorrespondEpilines(cv::Mat(selPointsRight),2,fundemental,linesRight);
for (vector<cv::Vec3f>::const_iterator it= linesRight.begin(); it!=linesRight.end(); ++it) {
// draw the epipolar line between first and last column
cv::line(imgLeft,cv::Point(0,-(*it)[2]/(*it)[1]), cv::Point(imgLeft.cols,-((*it)[2]+(*it)[0]*imgLeft.cols)/(*it)[1]), cv::Scalar(255,255,255));
}
// Display the images with points and epipolar lines
cv::namedWindow("Right Image Epilines");
cv::imshow("Right Image Epilines",imgRight);
cv::namedWindow("Left Image Epilines");
cv::imshow("Left Image Epilines",imgLeft);
*/
// 5] stereoRectifyUncalibrated():::::::::::::::::::::::::::::::::::::::::::::::::: | {
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javascript, jquery, require.js
verb.getRerunai = (function () {
verb.rerunai = verb.reru.slice(0, -1) + "ない";
})();
verb.getSeru = (function () {
if (verb.group === "3") {
if (verb.u === "する") {
verb.seru = "させる";
}
if (verb.u === "くる") {
verb.seru = "こさせる";
}
}
if (verb.group === "2") {
verb.seru = verb.withoutEnd + "させる";
}
if (verb.group === "1") {
verb.seru = verb.nai.slice(0, -2) + "せる";
}
})();
verb.getserunai = (function () {
verb.serunai = verb.seru.slice(0, -1) + "ない";
})();
verb.process = (function () { | {
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homework-and-exercises, orbital-motion, earth, sun, satellites
The dotted line is the orbit of the satellite at a height $h$ (I've exaggerated the height a bit to make the diagram clearer). All we have to do is calculate the angle $\theta$, because the time the satellite is in the Earth's shadow is simply:
$$ t = \tau \frac{2\theta}{2\pi} \tag{1} $$
where $\tau$ is the period of the satellite. It should be obvious from the diagram that the distance I've labelled as $d$ is equal to the radius of the Earth, $r$, and therefore:
$$ (r + h) \sin\theta = r $$
or:
$$ \theta = \arcsin \left( \frac{r}{r + h} \right) \tag{2} $$
Finally the period of the satellite, $\tau$, is given by:
$$ \tau = 2\pi\sqrt{\frac{(r+h)^3}{GM}} \tag{3} $$
where $M$ is the mass of the Earth and $G$ is Newton's constant. | {
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python, python-3.x, reinventing-the-wheel
Depending on how you interpret "built-in list methods", the following may be OK:
def reverse_list(s):
s[:] = s[::-1] | {
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c#, cyclomatic-complexity
// Select only the unique solutions
foreach (var solution in OperatorResult.GetUniqueSolutions(solutions))
Solutions.Add(solution);
}
The enum:
public enum Operator
{
Multiply = '*',
Subtract = '-',
Add = '+',
Divide = '/'
}
Solutions property:
public static DependencyProperty SolutionsProperty = DependencyProperty.Register("Solutions",
typeof (ObservableCollection<OperatorResult>), typeof (MainWindow));
public ObservableCollection<OperatorResult> Solutions
{
get { return GetValue(SolutionsProperty) as ObservableCollection<OperatorResult>; }
set { SetValue(SolutionsProperty, value); }
} | {
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pl.programming-languages, language-design
You made the insightful guess, that resumable exceptions are not a good idea in all contexts. They can make resource handling harder and more generally anything related to side-effects must be considered very carefully when you add new control-flow entry points to a block of code.
It is possible for the exception raising code to decide on whether it should be resumable or not. This is natural if you see resumable exceptions as a combination of usual exceptions and continuations: you raise an exception and, in the attached data, decide whether or not to include a continuation to the rest of the computation; the handler then decide whether or not to invoke that continuation, that is "resume" the exception. | {
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(reference). Simplify each to one trigonometric expression. Trigonometry definition, the branch of mathematics that deals with the relations between the sides and angles of plane or spherical triangles, and the calculations based on them. Tried in Radian mode and the results are$2. 62$and$11. The first four of these are known as the prosthaphaeresis formulas, or sometimes as Simpson's formulas. It includes topics covered. Some variations include the ability to “retrigger” the pulse, extending the output pulse duration with additional trigger signals. Honor Pre-Calculus. Trig Identities Practice test #1 High School PreCalculus / PreCal – 4A (Mr. Formulas Perfect Square Factoring: Difference of Squares: Difference and Sum of Cubes: B. Download as PDF file. The heart of the module is the study of precise definitions of sine and cosine (as well as tangent and the co-functions) using transformational geometry from high. Don’t name any variables or files the same as built-in MATLAB | {
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c++, graph
could potentially be declared const, which would be the expectation given their names. Or this new vector could be a local variable in the functions that need it, and passed to the other functions that need it as a parameter, which would be a necessary step (but not the only step) to make the class friendlier for multithreaded use. | {
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ros
Original comments
Comment by joq on 2011-09-21:
A new question makes sense. Ken already answered your original question as well as it can be.
Comment by 130s on 2011-09-21:
@joq thanks. I just updated the question body text (though I wonder if I should ask another question for this particular case).
Comment by fergs on 2011-09-20:
Just FYI, there should be very little difference between diamondback and electric for most APIs.
Comment by joq on 2011-09-20:
I know of no general document. Each API should describe its own changes over time. Specifically, what compile errors are you seeing?
ROS 0.4 is quite old -- that's a bit long for any docs to exist. In general, the release notes for each ROS Distribution should provide the major migration notes if you click on the relevant change lists. For Electric->Diamondback, there's very little changes for ROS code, though thirdparty libraries like Eigen require more significant migration.
http://www.ros.org/wiki/cturtle | {
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python, beginner, python-3.x, game
elif want_job == "n":
job_selection()
else:
print(colored("Invlid input. Try agian!", 'red'))
print('='*15)
job_selection()
elif change == "n":
print("Going back!")
print("="*15)
job_selection()
else:
print(colored("Invlid input. Try agian!", 'red'))
print("="*15)
job_selection()
elif Skill < 10:
print(colored("You don't have enough Skills to get the job! You need 10 Skills!", 'red'))
print("="*15)
job_selection()
elif job_position <= []:
if Skill >= 10:
if want_job == "y": | {
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general-relativity, differential-geometry
Title: How do I interpret this statement? This is about a derivation of the geodesic equation (Carrol, 2003), in which the author gave 2 definitions of the geodesic curve; the first one is that the tangent vector is parallel transported on the curve, and the second is that the curve is the extremal of the path length functional. I have no problem understanding everything but this paragraph:
What was hidden in our derivation of (3.47) was that the demand that the tangent vector be parallel transported actually constrains the parameterization of the curve, specifically to one related to the proper time by (3.58). | {
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machine-learning, deep-learning, tensorflow
up_conv8 = UpSampling2D(size=(2, 2), data_format="channels_last", name='up_conv8')(conv8)
ch, cw = get_crop_shape(conv1, up_conv8)
crop_conv1 = Cropping2D(cropping=(ch, cw), data_format="channels_last", name='crop_conv1')(conv1)
up9 = concatenate([up_conv8, crop_conv1])
conv9 = Conv2D(64, (3, 3), activation='relu', padding='same', data_format="channels_last", name='conv9_1')(up9)
conv9 = Conv2D(64, (3, 3), activation='relu', padding='same', data_format="channels_last", name='conv9_2')(conv9)
ch, cw = get_crop_shape(inputs, conv9)
conv9 = ZeroPadding2D(padding=(ch, cw), data_format="channels_last", name='conv9_3')(conv9)
conv10 = Conv2D(1, (1, 1), activation='sigmoid', data_format="channels_last", name='conv10_1')(conv9)
model = Model(inputs=inputs, outputs=conv10)
To compile the model I do:
model.compile(tf.keras.optimizers.Adam(lr=(1e-4) * 2), loss=dice_coef_loss, metrics=['accuracy']) | {
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classical-mechanics, terminology, hamiltonian-formalism, group-theory, lie-algebra
Take note that above a type 2 generating function is used. The different types of generating functions are related by Legendre transforms. See, e.g. Tong's notes for further details. | {
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fluid-dynamics, statistical-mechanics, navier-stokes
Integration of the equation of motions. If the flow velocity is constant in time, you can perform the integration analytically, and find the result
\begin{equation}
\mathbf{v}^{body}(t) = \dfrac{\mathbf{F}}{c} + \left( \mathbf{v}_0 - \dfrac{\mathbf{F}}{c} \right) e^{-\frac{c}{m}t} \ .
\end{equation}
If you integrate in time, and prescribe the initial condition on the position, you can find the position of the body as a function of time as well.
Terminal velocity. You can easily find the terminal velocity, letting $t \rightarrow \infty$,
\begin{equation}
\mathbf{v}^{term} = \dfrac{\mathbf{F}}{c} \ .
\end{equation} | {
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standard-model, quantum-chromodynamics, quarks
here is the solution: | {
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predictive-modeling
Let's further assume that you have data from past 3 weeks, which allows us to set following table. The rows contain individual calls, the columns the attributes. The appendix _1 tells us the time. So for example x1_1 is call duration previous week, x2_2 is time of call two weeks before etc.
client | x1_1 | x2_1 | x3_1 | x1_2 | x2_2 | x3_2 | ... | x3_3
You can train your model using historical data, where x3_3 is last week. Then, you will feed the model with current data (_3 is current week*) and try to predict x3_3 - whether the customer will pick the phone.
*I am assuming that you know who you are going to call, hence you have _3 attributes, but you don' know yet whether they respond or not
The aim is to give the model the opportunity to learn the time dependencies - maybe time of call week before together with call duration strongly correlate with future chance of picking up the phone again. | {
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from the source and in recursive call, all these vertices will act a source. These are used to calculate the importance of a particular node and each type of centrality applies to different situations depending on the context. EPP + 1 other. Another thing to keep in mind is the direction of relationships. More efficient algorithms might exist. A graph in which we can visit from any one vertex to any other vertex is called as a connected graph. Hence, in this case the edges from Fig a 1-0 and 1-5 are the Bridges in the Graph. This graph consists of three vertices and three edges. Kruskal's Algorithm with disconnected graph. Here is my code in C++. A graph such that for every pair of vertices there is a unique shortest path connecting them is called a geodetic graph. Since the edge set is empty, therefore it is a null graph. Views. And there are no edges or path through which we can connect them back to the main graph. Create a boolean array, mark the vertex true in the array once | {
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ros, pcl, iai-kinect2, frame-id, depth-image-proc
When I do rostopic echo /kinect2/filtered_image, I get:
header:
seq: 2139
stamp:
secs: 0
nsecs: 0
frame_id: ''
height: 1
width: 68227
encoding: bgr8
is_bigendian: 0
step: 204681 | {
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c++, strings, parsing, search, c++17
/**
* Find the first matching array in a larger array and return the argument index and buffer end index of the match.
* @param str One or many strings to search for
* @returns std::pair<argument index, end of match index in buffer>
*/
template <size_t... SS>
constexpr std::pair<int, size_t> find_first(const T (&...str)[SS]) const {
size_t matching[] { (SS - 1)... }; // Amount of remaining 'characters to match'
for (size_t i = 0; i < S; ++i) { // Loop over the dataset
int mi = 0;
((matching[mi++] = (str[(SS - 1) - matching[mi]] == values[i]) ? (matching[mi] - 1) : ((str[0] == values[i]) ? (SS - 2) : (SS - 1) )), ...); // Nasty pseudo loop for width first search
for (mi = 0; mi < sizeof...(SS); ++mi) { // See if we have any full matches
if (matching[mi] == 0) return { mi, i };
}
}
return { -1, 0 };
} | {
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javascript, sql, parsing, lexical-analysis
I'm now learning the hard way that this is not sustainable. I'm attempting to implement a proper lexer/parser before adding any new features.
Question
As someone with no experience writing a real lexer I started by reading a bunch of really dry tutorials in languages I don't really understand. The one thing they all seemed to have in common is that they check each character of the input string individually, which to me, seems tedious and unnecessary, so I decided to try it my own way, which turned out to be much, much simpler and shorter than implementations I found online.
If my implementation is so much better then why aren't other people doing something similar? There must be something wrong with this algorithm, what is it?
My Method | {
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cosmology, space-expansion, redshift, gravitational-redshift
At greater distances, the straight line curves and in addition one has to contend with the fact that the Hubble constant is not a constant.
Why $v = H_0 r$ for a uniform expansion is easily established by drawing a sequence of dots on a piece of paper, allowing the space between the dots to expand uniformly, and then asking what is the relationship between the relative velocity and separation of any of the dots at a particular time. | {
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Args:
n (int): number of uniform random variables in the summation.
s (int): number of samples used to evaluate the distribution.
rs (int): random seed.
Returns:
(float, float): the x and y data points of the approached CDF.
"""
arr = np.empty(s, dtype=np.float64)
np.random.seed(rs)
for i in prange(s):
c = 0.0
for k in range(n):
c += np.random.rand()
arr[i] = c
x = np.sort(arr)
y = np.arange(s) / np.float64(s)
return x, y
%%time
x, y = cdf_emp(n=10, rs=RS)
CPU times: user 461 ms, sys: 3.7 ms, total: 465 ms
Wall time: 463 ms
cmap = matplotlib.cm.get_cmap(CMAP)
ax = cdf_th_df.plot(
x="x", y="10", figsize=FS, alpha=0.6, label="Theoretical", c=cmap(0)
)
_ = ax.scatter(x, y, label="Empirical", alpha=0.6, s=50, color=cmap(0.8))
_ = ax.legend()
_ = ax.set(title="Theoretical and empirical CDF of $X_{10}$", xlabel="x", ylabel="y")
Actually we can do that for several values of $n$, as we did precedently with the analytical CDF: | {
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in relational calculus expression. Compute the Cartesian products of given sets: \[{A \times \left( {B \backslash C} \right) }={ \left( {A \times B} \right) \backslash \left( {A \times C} \right)}$, If $$A \subseteq B,$$ then $$A \times C \subseteq B \times C$$ for any set $$C.$$, $$\left( {A \times B} \right) \cap \left( {B \times A} \right)$$, $$\left( {A \times B} \right) \cup \left( {B \times A} \right)$$, $$\left( {A \times B} \right) \cup \left( {A \times C} \right)$$, $$\left( {A \times B} \right) \cap \left( {A \times C} \right)$$, By definition, the Cartesian product $${A \times B}$$ contains all possible ordered pairs $$\left({a,b}\right)$$ such that $$a \in A$$ and $$b \in B.$$ Therefore, we can write, Similarly we find the Cartesian product $${B \times A}:$$, The Cartesian square $$A^2$$ is defined as $${A \times A}.$$ So, we have. Other relational algebra operations can be derived from them. Any cookies that may not be particularly necessary for the website to function and | {
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Precalculus! These skills are organized into categories, and you can move your mouse over any skill name to preview the skill. All the best!. Trig Graphs Answer Section MULTIPLE CHOICE 1. 1 page 233 - 237 # 4ac, 5bd, 10ab, 12, 14, 20 Extensions: 15, 19ac, 24 (just ask yourself if it's periodic), C2 5. 71 m ____ 2. Test your knowledge. Cannot exceed 1 since always lies between -1 and 1. The trigonometric functions are also known as the circular functions. Amplitude = a Period = or Horizontal Shift = c Vertical Shift = d Steps to sketch 1. 758-759) Chapter Assessment 1 1 1 0. TI-Nspire users can have students immediately see their results. Do secant graphs have "amplitude?" Why or why not? 6. Given some algebraic relation that connects different dynamical quantities we can differentiate implicitly. • Be able to write an equation of a trigonometric function given the characteristics of that function. If you don't have one yet, you can use Wolfram Alpha in the meantime. Edexcel AS pure | {
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fourier-transform, laplace-transform
$$X_L(s)=\frac{1}{s+a}\tag{1}$$
Since $a>0$, the ROC of $X_L(s)$ contains the imaginary axis, and the Fourier transform of $x(t)$ is simply obtained by evaluating $X_L(s)$ on the imaginary axis $s=j\omega$:
$$X_F(\omega)=X_L(j\omega)=\frac{1}{j\omega+a}\tag{2}$$
Since $s=\sigma+j\omega$ is generally complex, not only the Fourier transform but also the Laplace transform $(1)$ has a real and an imaginary part:
$$X_L(\sigma+j\omega)=\frac{1}{\sigma+j\omega+a}=\frac{\sigma+a}{(\sigma+a)^2+\omega^2}-j\frac{\omega}{(\sigma+a)^2+\omega^2}\tag{3}$$
Only when evaluated on the real axis $s=\sigma$ ($\omega=0$) does the imaginary part vanish. | {
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machine-learning, data-sets
Title: benchmark data set for Metareasoning problem I am developing algorithm for solving following problem:
Given a set of items with unknown feature(s) (but know distribution of feature(s)). Algorithm must choose what items to measure(every measure has some cost)). I use Value of information theory to find this measurements.
After measurements are done algorithm choose K best items from the set, using some utility function that depends on feature values of items.
I crafted few synthetic data sets, but perhaps there are some benchmark data sets that are used for this kind of problems?
Regards. In this sort of situation, two standard answers are: | {
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similarly 21 - 10 = 11 which is RHS(deviation) and LHS is (deviation + number ) 21 + 11 = 32
so square root is 32_
Now sqaure of 11 is 121 but since it is base of 10 take only 1 put in dash(321) and add 12 to 2 of the LHS which is 32
That gives you 2 + 12 = 14 where 1 is carry and gets added to 3 and become 4, so finally square root is 441
Now from here go in the reverse direction
2+44 = 46 with 4 carry added to 5 becomes 96 and square root as 961 for 31
take the last number from 961 which is 1 and put it in 72_ and add 96 to 2 of 72 which gives 96+2 = 98 and carry as 9 which to be added to 7 and 7+9 = 16 combining 1681 is the square of 41
0 0
Senthilkumar
2014-03-05 14:05:45
41
41 *
-------
41
164
-------
1681 Ans
isn't that simple?
0 0
jisstpalelil
2014-04-15 07:31:51
U r right senthilkumar, this trick is not much easy 4 such no.
0 0
sweetdreams
2013-09-25 05:03:59
36^2=(3*10)+6
to find rhs: 6^2=36
base has only 1 zero, therefore 3 is a carry | {
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the best input arguments to obtain the minimum value of a real function, called in this case, cost function. Fundamental theorem of linear programming If the optimal (maximum or minimum) value of the objective function in a. Common benzodiazepines used for GAD include alprazolam, clonazepam, diazepam, and lorazepam. For what number of bars is the unit cost at its mimimum? What is the unit cost at that level of production? Haven't got a clue what this problem is asking of me. Actual costs refer to real transactions, wherease opportunity costs refer to the alternative taken into consideration by decision makers who might want to choose the line of activity which minimise the costs. Average cost is minimized when average cost = marginal cost is another saying that isn’t quite true; in this case, the correct statement is: Average Cost has critical points when Average Cost and Marginal Cost are equal. LP problems seek to maximize or minimize some quantity (usually profit or cost). Find the | {
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It's not only italicization, it's proper spacing and in some cases positioning of subscripts and superscripts. For example $\displaystyle a \lim_{x\to\infty} b$. Note the spacing before and after "$\lim$" and notice where the subscript is. – Michael Hardy Apr 11 '12 at 21:37
@joriki, now is valid to do $\newcommand{\tr}{\operatorname{tr}}$ so that you can use \tr later in your post. – leo Apr 11 '12 at 23:41 | {
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urdf, ros-electric, nao
Originally posted by Curious Joe on ROS Answers with karma: 1 on 2012-06-27
Post score: 0
Hi. I had the same problem with the 'planning_models' package in 'armnavigation' stack. You need to edit manifest.xml of the urdf package and append '-ltinyxml' to the 'cpp cflags' line.
The resulting line looks like:
<cpp cflags="-I${prefix}/include" lflags="-Wl,-rpath,${prefix}/lib -L${prefix}/lib -lurdf -ltinyxml"/>
Originally posted by Jürgen Kunz with karma: 36 on 2012-07-24
This answer was ACCEPTED on the original site
Post score: 2
Original comments
Comment by AHornung on 2012-07-24:
I would recommend creating ticket for this fix in the bug tracker for URDF. | {
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quantum-field-theory, condensed-matter, renormalization, critical-phenomena
...the 3D Ising CFT is the only $\mathbb{Z}_2$-symmetric CFT in 3 dimensions with exactly two relevant operators. | {
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quantum-mechanics, atomic-physics, quantum-chemistry
In other words, the energy of the $2p^2\ {}^3P^e$ state, $E=-0.125\,355\,451\,24 \:\rm a{.}u.$ as calculated by Bylicki and Bednarz, is strictly below $E= -\frac18\:\rm a{.}u.$, which is the minimal energy needed to get to the $2s$ or $2p$ states of neutral hydrogen coupled with a free electron, so that continuum is not energetically available.
Instead, the only available continuum is the $N=1$ continuum, i.e. a neutral hydrogen in the ground $1s$ state coupled with a free electron. Since this is energetically available (with the continuum starting at $E= -\frac12\:\rm a{.}u.$), the $2p^2\ {}^3P^e$ state could in principle be autoionizing, i.e., it could in principle spontaneously fly off into states in that continuum. However, for this to happen directly, the relevant continuum state needs to share the same quantum numbers ($^3 P^e$, i.e., a triplet $S=1$ state, total angular momentum of $L=1$, and even parity under spatial inversion) and this is no longer possible. | {
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for distance between parallel lines is Think about that; if the planes are not parallel, they must intersect, eventually. It doesn’t matter which perpendicular line you choose, as long as the two points are on the lines. CBSE Previous Year Question Papers Class 10, CBSE Previous Year Question Papers Class 12, NCERT Solutions Class 11 Business Studies, NCERT Solutions Class 12 Business Studies, NCERT Solutions Class 12 Accountancy Part 1, NCERT Solutions Class 12 Accountancy Part 2, NCERT Solutions For Class 6 Social Science, NCERT Solutions for Class 7 Social Science, NCERT Solutions for Class 8 Social Science, NCERT Solutions For Class 9 Social Science, NCERT Solutions For Class 9 Maths Chapter 1, NCERT Solutions For Class 9 Maths Chapter 2, NCERT Solutions For Class 9 Maths Chapter 3, NCERT Solutions For Class 9 Maths Chapter 4, NCERT Solutions For Class 9 Maths Chapter 5, NCERT Solutions For Class 9 Maths Chapter 6, NCERT Solutions For Class 9 Maths Chapter 7, NCERT Solutions For | {
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c#
Title: Find lowest leaf nodes in a binary tree So this is probably a popular problem, and I decided to take a crack at it today using C#.
I came up with the following solution:
private BinaryTree<int>.BinaryTreeNode FindLowestNodes(BinaryTree<int>.BinaryTreeNode node, int depth, ref int biggestDepth) {
this.WriteResult("Entering recursiorn for node.....{0}", node.Value.ToString());
BinaryTree<int>.BinaryTreeNode lowestNode = null;
if (node.Left != null) {
var n = FindLowestNodes(node. Left, depth + 1, ref biggestDepth);
if (n != null) lowestNode = n;
}
if (node.Right != null) {
var n = FindLowestNodes(node.Right, depth + 1, ref biggestDepth);
if (n != null)
lowestNode = n;
}
if (node.Left == null && node.Right == null) {
if (depth > biggestDepth) {
lowestNode = node;
biggestDepth = depth;
}
}
return lowestNode;
} | {
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things are worth pointing out: the dirst term is the "DC" voltage. A good starting point for understanding the relevance of the Fourier series is to look up the math and analyze a square wave. Use of Fourier Series. This movie cleverly demonstrates what Fourier Series really gives us. The wave length is. The Fourier transform can be applied to continuous or discrete waves, in this chapter, we will only talk about the Discrete Fourier Transform (DFT). Waveforms with a steeper slope than this may be subject to a form of distortion, known as slew rate distortion, which will not affect a pure sine wave. The connection with the real-valued Fourier series is explained and formulae are given for converting be-tween the two types of representation. A1 and A2 respectively. ES 442 Fourier Transform 3 Review: Fourier Trignometric Series (for Periodic Waveforms) Agbo & Sadiku; Section 2. THE CONNECTION TO THE FOURIER SERIES IAN ALEVY Abstract. the signal and the sine wave or cosine wave at that | {
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} |
We can clearly see that at least one of them has to be negative, in fact, just one variable can be positive at most. WLOG assume $$b,c<0$$ and $$a>0$$, then:
$$b+c < 0$$ and $$a^n >0 \Rightarrow b+c \neq a^n$$ and there would be no solution. If just two are negative you can follow the same argument.
Case 2: $$a=b \neq c$$
The system will transform into:
$$2a = c^n$$ $$a+c = a^n$$
Here, we can apply the same considerations as before:
• $$n$$ is odd
• At least one variable has to be negative.
Both variables can't be negative, you can prove that by using the same argument we used in case $$1$$. Wlog, assume $$c$$ is negative.
Now:
$$a+c= a^n > 0$$ $$a> -c$$ $$\vert a \vert > \vert c\vert$$
$$\vert 2a \vert > \vert 2c\vert$$ $$\vert c^n \vert > \vert 2c\vert$$ $$\vert {c}^{n-1} \vert> 2 \Rightarrow \vert c\vert > 1$$
That's correct since $$-c>0$$
Also:
$$a+c = a^n$$ $$1+\frac {c}{a} = a^{n-1} \Rightarrow a^{n-1}<1 \Rightarrow a< 1 \Rightarrow \vert a\vert < 1$$ | {
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"url": "https://math.stackexchange.com/questions/3237809/find-the-solutions-of-the-system-of-equations-ab-cnbc-anca-bn"
} |
conservation-laws, field-theory
$$
\frac{\partial \rho}{\partial t}=-\vec\nabla\cdot\vec{j}
$$
This says that the divergence of the current $\vec{j}$ is equal and opposite to the change in the density. Put another way, if you consider an infinitesimal volume, the current flux out of the boundary of the volume exactly equals the decrease in the density within the volume. This is usually what we mean when we say something (say a fluid) is conserved: If the fluid is flowing out of an area, the density (concentration of the fluid) decreases proportionately.
Note that if you assume that all currents go to zero at infinity, you can also make a global claim that you might recognize more as a conservation law:
$$
\frac{\partial}{\partial t}\int \rho = -\int\vec\nabla\cdot\vec j= 0
$$ | {
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No, not always. For example, it might be that the n students all answer the m questions in exactly the same way. Knowing that each had i questions correct and m- i questions wrong tells us nothing about which answer were correct and which wrong.
Indeed, but in that case i should transform my question to ask about a GENERAL and STRAIGHTFORWARD(i.e to be programmed) way to find if the string of the correct answers can be found or not and if it can, to find it(with a general and straightforward way).... | {
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