text stringlengths 1 1.11k | source dict |
|---|---|
entanglement, non-locality, bell-experiment, correlations, nonlocal-games
[$\dagger$]: John Preskill - Introduction to Quantum Information (Part 1) - CSSQI 2012 (timestamp included)
[$\dagger \dagger$]: John Preskill - Introduction to Quantum Information (Part 2) - CSSQI 2012 (timestamp included)
I do understand that the sum of these three probabilities is greater
than one because there are some constraints already involved; like if
we uncover all three coins at least two have to be the same. So
naturally, there's some redundancy leading to a sum of probabilities
that is greater than one! | {
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# Definitions of Continuity in Topological Spaces ... Sutherland, Defintions 8.1 and 8.2 ... ...
#### Peter
##### Well-known member
MHB Site Helper
I am reading Wilson A. Sutherland's book: "Introduction to Metric & Topological Spaces" (Second Edition) ...
I am currently focused on Chapter 8: Continuity in Topological Spaces; bases ...
I need some help in order to prove Definition 8.1 is essentially equivalent to Definition 8.2 ... ...
Definitions 8.1 and 8.2 read as follows: ... ...
In the above text we read the following:
" ... ... Then one can prove that $$\displaystyle f$$ is continuous iff it is continuous at every point of $$\displaystyle X$$. ... ... "
I sketched out a proof of the above statement ... but am unsure of the correctness/validity of my proof ...
My sketch of the proof is as follows ...
First assume f is continuous (Definition 8.1 holds true) ... ...
We are given (Definition 8.2) that $$\displaystyle U' \in T_Y$$ where $$\displaystyle f(x) \in U'$$ ... ... | {
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proteins
alignment = pairwise2.align.globalxx(''.join(seq).replace('?',''), "ACQQG")[0]
alignments is a tuple of the MSA sequences.
If you want to do the latter without coding. Extract the sequence from the PDB using PyMOL the normal application and load the pdb and then print cmd.get_fastastr('chain A') in the command line part of the GUI. Copy this. Go to Muscle or other onliner aligner and align! | {
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c#, enum
foreach (Opportunities Opp in OpportunitiesList)
{
if (SelectedOppType == 1 && Opp.OpportunityStatusID == OpportunityStatus.Active) // Opp.OpportunityStatusID == OpportunityStatus.Draft
{
FilterdOppsList.Add(Opp);
}
else if (SelectedOppType == 2 && Opp.OpportunityStatusID == OpportunityStatus.Draft)
{
FilterdOppsList.Add(Opp);
}
else if (SelectedOppType == 3 && Opp.OpportunityStatusID == OpportunityStatus.Closed)
{
FilterdOppsList.Add(Opp);
}
else if (SelectedOppType == 4 && (Opp.OpportunityStatusID == OpportunityStatus.Active || Opp.OpportunityStatusID == OpportunityStatus.Draft))
{
FilterdOppsList.Add(Opp);
}
else if (SelectedOppType == 5)
{
FilterdOppsList.Add(Opp);
}
}
foreach (var OppItem in FilterdOppsList)
{
Console.WriteLine(OppItem.OppText);
} | {
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finite-automata
Title: What does $\sigma(t_0, \ldots, t_{n-1}) \in \mathcal{T}_{\Sigma}^{0}$ in this paper mean? The paper is "Mappings and Grammars on Trees" by William C. Rounds. There was a definition of ranked alphabet in page 3 and I can't understand the second part of the definition.
Definition. A ranked alphabet is a pair $(\Sigma, r)$ where $\Sigma$ is finite, and $r: \Sigma \rightarrow \mathbb{N}$.
We set $\Sigma_n = r^{-1}\{n\}$
Let $(\Sigma, r)$ be a ranked alphabet. The set $\mathcal{T}_{\Sigma}^{0}$ (the constant $\Sigma$-terms) is the smallest set of strings such that:
$\ldots$
(b) if $t_0, \ldots, t_{n-1} \in T_{\Sigma}^{0}$, and $\sigma \in \Sigma_{n}$, then $\sigma(t_0, \ldots, t_{n-1}) \in \mathcal{T}_{\Sigma}^{0}$ | {
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possible outcomes. Solution for Which of the following sampling procedures involve the use of probability sampling? a. So, when you know the probability of event A, you can fi nd the probability of the complement of event A. ' Vary the size of the target and repeat the experiment. Darts Probability 2 - Displaying top 8 worksheets found for this concept. The Small Circle On The Inside Has Radius Of 5in. To generate the CS109 logo, we are going to throw half a million darts at a picture of the Stanford seal. Each dart strikes a board randomly. The probability, $$p$$, of a success and the probability, $$q$$, of a failure are the same for each trial. Assuming that the dart hits at least some part of the circle within the outermost circle and hitting all points in the entire area is equiprobable, the probability of hitting the green region is proportioanl to its area as compared to the total area of the outermost circle. If the dart is equally likely to hit any point on the target, what is | {
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"openwebmath_score": 0.5500837564468384,
"tags": null,
"url": "http://clodd.it/cfop/probability-darts-answers.html"
} |
machine-learning, metric
Title: Average precision, balanced accuracy, F1-score, Matthews Correlation Coefficient, geometric means Average precision, balanced accuracy, F1-score, Matthews Correlation Coefficient, geometrics means are the few evaluation metrics for imbalanced data. However, all this metrics can lead to different 'best' model. How do we then decide which is indeed the 'best' model? It's about designing the task properly. I'm not talking about the design of the model, and this is not either about selecting an evaluation based on the characteristics of the data (e.g. there's no simple way to decide based on whether the data is imbalanced or not).
The design of standard tasks is usually established in the state of the art. Take machine translation (MT) for example, there is a whole area of research devoted to evaluating MT, with various simple and advanced evaluation measures designed specifically for the task. | {
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So how can I get $|E[Y\mid{\mathcal G}]|\leq c$ using $|Y|\leq c$?
-
First $$\left|E[Y\mid\mathcal G]\right|\leq E[|Y|\mid \mathcal G]$$ by Jensen's inequality. Now, let $Z=E[|Y|\mid \mathcal G]$, then for every $G\in\mathcal G$ we have $$\int_G Z=\int_G|Y|\,\mathrm dP\leq \int_G c\;\mathrm dP,$$ and since both $Z$ and $c$ are non-negative and $\mathcal{G}$-measurable, we have that $Z\leq c$ almost surely.
To see that the last statement is true, we consider the non-negative random variable $(Z-c)1_{\{Z>c\}}$ which has mean $0$ as $$0\leq E\left[(Z-c)1_{\{Z>c\}}\right]= \int_{\{Z>c\}} Z\,\mathrm dP-\int_{\{Z>c\}} c\,\mathrm dP\leq 0$$ since ${\{Z>c\}}\in\mathcal{G}$. This implies $(Z-c)1_{\{Z>c\}}=0$ a.s. and hence $Z=c$ a.s.
-
thank you for your answer. how do you come up with the last sentence? – Jack Nov 29 '12 at 21:27
@Jack: See the edit. – Stefan Hansen Nov 30 '12 at 6:24 | {
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entanglement
Title: What is a general entangled bipartite system? Is there a general pure entangled bipartite system that all other entangled bipartite systems are a special case of it? I didn't see the question asked about pure states - then yes! A general entangled pure state takes the following form, via the Schmidt decomposition:
$$|\Psi\rangle=\sum_i \psi_i |a_i\rangle\otimes |b_i\rangle$$ for some non-negative coefficients $\psi_i$ and some pure states $|a_i\rangle$ and $|b_i\rangle$. To be entangled, more than one of the coefficients $\psi_i$ must be nonzero. This is a bit of a strange way of writing the set, but we can be clever and say that any state of the form of $|\Psi\rangle$ with all Schmidt coefficients $|\psi_i|<1$ is entangled. Unentangled states are those with the same form but with one of the coefficients having magnitude equal to unity. | {
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With your help, this is the proof that I have come up with if anyone reading this at a later time is interested.
My Solution :
First, suppose that $m(\mathbb R) = n(\mathbb R) < \infty$. We show that $m=n$ on $\mathcal B$. Consider the collection $\mathcal G = \{B \in \mathcal B: m(B) = n(B)\}$. We observe that $\mathcal G$ is a monotone class:
Suppose $A_i \uparrow A$ where $A_i \in \mathcal G$ for all $i \in \mathbb N$ and define $B_1 = A_1$, $B_2 = A_2 - A_1$, $\dots$, $B_n = A_n - \cup_{i=1}^{n-1}A_i$ so that $\cup_{i=1}^\infty A_i = \cup_{i=1}^\infty B_i$ where $\{B_i\}$ are pairwise disjoint. Notice that for $C,D \in \mathcal G$ with $C \subset D$, we have $$m(D-C) = m(D) - m(C) = n(D) - n(C) = n(D-C),$$ since $m$ and $n$ are finite measures. So $B_i \in \mathcal G$ for all $i \in \mathbb N$. Then $A \in \mathcal G$, since $$m(A) = m(\cup_{i=1}^\infty B_i) = \sum_{i=1}^\infty m(B_i) = \sum_{i=1}^\infty n(B_i) = n(\cup_{i=1}^\infty B_i) = n(A)$$ | {
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} |
If you find this tool interesting, perhaps you'll also enjoy some of our other related tools listed below:
## FAQ
### What are the odds of winning a toss coin?
The odds of winning a toss coin is one is to one, or 1/1 in fractional odds format. Coins usually have two sides (i.e., heads and tails), and every flip of a coin results in either a win or loss. Since there is one chance of winning and one chance of losing a coin toss, the odds of winning (or losing) a coin toss is, therefore: 1 ÷ 1 = 1/1, or one is to one.
### How do I convert fractional odds to decimal odds?
To convert fractional odds to decimal odds, taking the losing odds to be 1/2:
1. First, add the denominator of the fractional odds to its numerator. For our example, we get: 1 + 2 = 3.
2. Then, divide the sum we get by the denominator to obtain: 3 ÷ 2 = 1.5.
That's it! The decimal odds equivalent of 1/2 fractional odds is 1.5. | {
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ros, rviz, collada-urdf
Title: COLLADA from Sketchup is wrong colors
I've update a robot description that previously used STL files (created from Solidworks) to use COLLADA files. Everything worked fine before, just wanted to make it prettier - i.e. add colors to the model.
I imported the STLs into SketchUp 8 using some plugin, and that went well. Upon adding correct colors, I exported to COLLADA using Sketchups builtin exporter. This is a screenshot of SketchUp with the correct colors:
neobotix platform SketchUp http://farm8.staticflickr.com/7091/7402536638_8cf443cb26.jpg
Problem is that the COLLADA file comes up with wrong colors in Rviz:
neobotix platform Rviz http://farm8.staticflickr.com/7096/7402561412_b8a810b481.jpg
I have tested the following:
Use in model (Rviz) - Colors look too dark (see screenshot)
Open in Meshlab - No colors
Open in Preview.app on OSX - Colors look good
Please advice, and thank you in advance!
COLLADA file
SketchUp file | {
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• Why in the first passage did you switch the minus sign with a plus? – user228113 Aug 31 '16 at 16:12
• The series $\sum_{n\geq 1}\frac{2n}{4n^2-1}$ is not converging. – Jack D'Aurizio Aug 31 '16 at 16:13
The work in the OP has some flaws. Note that we have for all $$x$$, $$\left|\frac{\cos(2nx)}{4n^2-1}\right| \le \frac1{4n^2-1}$$, for each $$n$$. Inasmuch as
\begin{align} \sum_{n=1}^\infty \frac{1}{4n^2-1}&<\infty \end{align}
the Weierstrass M-Test guarantees that the series $$\sum_{n=1}^\infty \frac{\cos(2nx)}{4n^2-1}$$ converges uniformly for all $$x\in [-\pi,\pi]$$.
To analyze whether the series is differentiable, we examine the series of term-by-term derivatives $$D(x)$$ as given by
$$D(x)=-2\sum_{n=1}^\infty \frac{n\sin(2nx)}{4n^2-1} \tag 1$$
Note that $$\sum_{n=1}^N \sin(2nx)=\csc(x)\sin(Nx)\sin((N+1)x)$$ is bounded by $$|\csc(x)|$$ for $$x\ne 0,\pi,-\pi$$. Furthermore, $$\frac{n}{4n^2-1}$$ monotonically decreases to $$0$$ as $$n\to \infty$$. | {
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python, performance, numpy
'''theta = i_minus_k**2 * j_minus_l # 437 ms
result = S1_slid * (
np.cos(theta) - 1j * np.sin(theta)
)
return result'''
# 268 ms
theta = -i_minus_k**2 * j_minus_l
rect = np.empty((*S1_slid.shape, 2), dtype=np.float64)
np.cos(theta, out=rect[..., 0])
np.sin(theta, out=rect[..., 1])
as_complex = rect.view(dtype=np.complex128)[..., 0]
as_complex *= S1_slid
return as_complex
def make_addends(S1_slid: np.ndarray, N: int):
# Numeric indices over any of the dimensions
idx = np.arange(N)
# Broadcast index difference to two-dimensional matrix
idx_diff = idx[:, np.newaxis] - idx
# Four-dimensional term: (j - l)
j_minus_l = idx_diff[np.newaxis, np.newaxis, :, :]
# Four-dimensional term: (i - k)
i_minus_k = idx_diff[:, :, np.newaxis, np.newaxis]
# Full addends before triangularisation
addends = addend_expr(S1_slid, i_minus_k, j_minus_l)
# Triangularise
return np.tril(addends) | {
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algorithms, complexity-theory, algorithm-analysis, time-complexity
We will get the following array:
$$0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0$$
Now, intuitively I can see why this is the worst case for the algorithm and where $logn$ comes from, but I can't prove it properly.
As a side note I would appreciate any pointers toward where one can practice these kind of problems (concrete algorithms time complexity analysis, preferably with answers/explanations) Let an array $a[1],\ldots,a[n]$ be given. For an index $i$, let $\ell(i)$ be the largest $\ell$ such that $\{i-\ell,\ldots,i+\ell\} \subseteq \{1,\ldots,n\}$ and $a[i]$ is larger than all elements $a[i-\ell],\ldots,a[i-1],a[i+1],a[i+\ell]$. It is not difficult to see that the running time of the algorithm on the array is $\Theta(n + \sum_{i=1}^n \ell(i))$.
This prompts the following definition: | {
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ros, 3d-navigation, ros-electric, rosmake, sbpl
/usr/include/boost/detail/container_fwd.hpp:84: error: provided for ‘template<class Key, class Compare, class Allocator> struct std::set’
/home/bcddivad/code/ros/bcddivad_3d_navigation/arm_navigation_metrics/planning_models/src/kinematic_model.cpp:242: error: invalid type in declaration before ‘;’ token
/home/bcddivad/code/ros/bcddivad_3d_navigation/arm_navigation_metrics/planning_models/src/kinematic_model.cpp:250: error: request for member ‘insert’ in ‘joint_set’, which is of non-class type ‘int’
/home/bcddivad/code/ros/bcddivad_3d_navigation/arm_navigation_metrics/planning_models/src/kinematic_model.cpp:253: error: wrong number of template arguments (1, should be 3)
/usr/include/boost/detail/container_fwd.hpp:84: error: provided for ‘template<class Key, class Compare, class Allocator> struct std::set’
/home/bcddivad/code/ros/bcddivad_3d_navigation/arm_navigation_metrics/planning_models/src/kinematic_model.cpp:253: error: expected initializer before ‘it’ | {
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pressure, aerodynamics, atmospheric-science, buoyancy
Title: Balloon aerodynamics In this recent anime that I have seen, there is a part where an atomic bomb is sent to the stratosphere in a box, by a helium balloon.
As you can see in this picture of the set-up, there is a tube attached to the bottom of the helium balloon as it is ascending. I wanted to know what this tube is called, and what function is has for the aerodynamics of the balloon.
Basically, why is it there? If the balloon was completely isolated from the outside atmosphere and contained a certain gas (in this case helium), then the helium will exert a pressure outwards, attempting to expand the balloon. The atmosphere outside will also exert a pressure inwards, attempting to keep the balloon in a small shape. These two forces compete, and the balloon will always form a shape that exactly balances these two pressures, i.e. the net pressure acting upon the balloon surface is 0. | {
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classical-mechanics, newtonian-mechanics, rotational-dynamics
However, I'm not sure if this helps me find how much impulse is used towards the translational versus rotational momentum of the disk in the general case of the original problem.
Is there a basic law of mechanics that I'm missing and need to apply in order to understand this system? I feel like I'm missing something conceptually... This puzzle confused me too a long time ago, and the answer you get is absolutely right. If you apply the same impulse on the side, the disk will still translate with the same linear momentum, but it will also rotate around the center. The rotation is given by the angular momentum impulse, which is the torque $Fr$ times the increment of time. | {
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____________________________________________________________________
Reference
1. Engelking, R., General Topology, Revised and Completed edition, Heldermann Verlag, Berlin, 1989.
2. Hart, K. P., Nagata J. I., Vaughan, J. E., editors, Encyclopedia of General Topology, First Edition, Elsevier Science Publishers B. V, Amsterdam, 2003.
____________________________________________________________________
$\copyright \ 2014 \text{ by Dan Ma}$
# An example of a normal but not Lindelof Cp(X)
In this post, we discuss an example of a function space $C_p(X)$ that is normal and not Lindelof (as indicated in the title). Interestingly, much more can be said about this function space. In this post, we show that there exists a space $X$ such that | {
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homework-and-exercises, statics
Edit
Here are some numbers required to tip it over by putting a weight on the edge. A weight on the edge creates a torque, $\tau_W$, that will try to tip the table by rotating it around the bottom edge of the legs. The weight of the table creates a torque, $\tau_T$, that will prevent tipping. The table will tip when
$$\tau_W > \tau_T$$
Using Gert's notation below,
$$F(\frac{L_T-L_L}{2}) > (F_T + F_L)\frac{L_L}{2}$$
$$F > (F_T + F_L)\frac{L_L}{L_T-L_L}$$
$$= (281 lb + 4*55lb) \frac{16"}{40" - 16"}$$
$$= 334 \space lb$$
So a couple medium large people could tip it over by leaning on it or trying to climb onto it. Or a strong person could tip it by trying to pick it up by one side.
If you widen the base, it quickly gets better. Here are some numbers. I get that the artistic vision is a floating table top with a strong but recessed base. Perhaps your designer would be open to a trapezoidal base. Even with a wider base, the forces on the joint get stronger than you might suppose. | {
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quantum-gate, matrix-representation
1 &
0 \\
0 &
-1
\end{bmatrix},
\end{equation}
A $\operatorname{CNOT}_{12}$ gate is
\begin{equation}
\operatorname{CNOT}_{12} = \vert 0 \rangle \langle 0 \vert \otimes \mathbb{I} + \vert 1 \rangle \langle 1 \vert \otimes \sigma_x = \vert 0 \rangle \langle 0 \vert \otimes \mathbb{I} + \vert 1 \rangle \langle 1 \vert \otimes \begin{bmatrix}
0 &
1 \\
1 &
0
\end{bmatrix},
\end{equation}
Which means,
\begin{equation}
\operatorname{CNOT}_{12} = (\mathbb{I} \otimes R^{\pi/2}_y) \cdot \operatorname{CPHASE}_{12} \cdot (\mathbb{I} \otimes R^{-\pi/2}_y)
\end{equation} | {
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homework-and-exercises, thermodynamics, temperature, ideal-gas
the definition of C a little. Rather than associating C with the path dependent heat Q, in thermodynamics, we associate C with parameters relating to the state of the material being processed, in particular internal energy U and enthalpy H. We define the heat capacity at constant volume $C_v$ as the derivative of the internal energy U with respect to temperature at constant volume: | {
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Chapter 7 Formulas sheet. You peer around a corner. Now let's move on to the calculus chapters. Significant examples illustrate each topic, and fundamental physical applications such as Kepler’s Law, electromagnetism, fluid flow, and energy estimation are brought to prominent position. You may click on either the VIDEO link or the YouTube link, whichever works better for you. com-2021-01-28T00:00:00+00:01 Subject: Application Of Vector Calculus In Engineering Field Ppt Keywords: application, of, vector, calculus, in, engineering, field, ppt Created Date: 1/28/2021 1:25:40 PM. Among them are physics, engineering, economics, statistics, and medicine. Calculus – differentiation, integration etc. but goes on to introduce you to the subject of Vector Calculus which, like it says on the can, combines vector algebra with calculus. 3blue1brown. The following files are in PDF format. between definite and indefinite integrals. Siyavula's open Mathematics Grade 12 textbook, chapter 6 on | {
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"tags": null,
"url": "http://zveg.1upload.de/application-of-calculus-ppt.html"
} |
homework-and-exercises, special-relativity, kinematics, momentum, mass-energy
Title: Relating $p, E,$ and $m$ to $\gamma$ and $\beta$ (Special relativity) In my QFT textbook this relation appeared $$\frac{p}{E + m} = \frac{\gamma - 1}{\gamma\beta},$$ where $p$ is $|\vec{p}|$, the modulus of the momentum, $E$ is the energy, $m$ the mass, $\beta = V$ (we're considering $c = 1$) and $\gamma = 1/(1 - \beta^2)$. I've tried manipulating this for a while and still can't prove it. Any help would be much appreciated. It follows straightforwardly from $E=\gamma m$ and $p=\gamma\beta m$. | {
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javascript, performance, ecmascript-6, html5, canvas
repeatBlock("tp", 38, 39, level1_1Overworld[10]);
repeatBlock("p", 46, 47, level1_1Overworld[10]);
repeatBlock("p", 57, 58, level1_1Overworld[10]);
repeatBlock("s", 136, 137, level1_1Overworld[10]);
repeatBlock("s", 140, 141, level1_1Overworld[10]);
repeatBlock("s", 150, 152, level1_1Overworld[10]);
repeatBlock("s", 155, 156, level1_1Overworld[10]);
repeatBlock("s", 183, 189, level1_1Overworld[10]);
repeatBlock("tp", 28, 29, level1_1Overworld[11]);
repeatBlock("p", 38, 39, level1_1Overworld[11]);
repeatBlock("p", 46, 47, level1_1Overworld[11]);
repeatBlock("p", 57, 58, level1_1Overworld[11]);
repeatBlock("s", 135, 137, level1_1Overworld[11]);
repeatBlock("s", 140, 142, level1_1Overworld[11]);
repeatBlock("s", 149, 152, level1_1Overworld[11]);
repeatBlock("s", 155, 157, level1_1Overworld[11]);
repeatBlock("tp", 163, 164, level1_1Overworld[11]);
repeatBlock("tp", 179, 180, level1_1Overworld[11]);
repeatBlock("s", 182, 189, level1_1Overworld[11]); | {
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inorganic-chemistry, thermodynamics, halides
The fluorides
As shown in your graph, the trend for the metal fluorides is that going from $\ce{LiF}$ to $\ce{CsF}$, $-\Delta_\mathrm{f}H(\ce{MF})$ decreases, i.e. $\Delta_\mathrm{f}H(\ce{MF}) = \Delta H_\mathrm{tot}$ increases (it becomes less negative). Here, the halide ion $\ce{X-}$ is not changing, so $\Delta H_\ce{X}$ is a constant and we only need to consider the other two terms:
Going from $\ce{Li}$ to $\ce{Cs}$, the atomisation enthalpy decreases and the first ionisation energy decreases. That means that $\Delta H_\ce{M}$ decreases.
Going from $\ce{Li}$ to $\ce{Cs}$, the radius of the metal ion increases, and so the lattice enthalpy decreases. This means that $\Delta H_\ce{MX}$ (which is the negative of the lattice enthalpy) increases. | {
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Last edited: Feb 22, 2010
3. Feb 22, 2010
### artbio
So:
$$E[max(x_1,...,x_n)]=\int_0^k \! max(x_1,...,x_n)\frac{1}{k} \, dx=\frac{1}{k}\int_0^k \!max(x_1,...,x_n)\, dx$$
Is this correct?
Now I have a problem. Since the "max" is also a random variable, for which I don't know the density function. How do I integrate this?
4. Feb 22, 2010
1) You are dealing with a random sample of size $$n$$, so the individual $$x_i$$ are independent
2) I'll call the maximum of the variables $$M$$ (non-standard, but it will work) The cumulative distribution function of the maximum is, by definition,
$$F(t) \equiv P(M \le t)$$
3) If the maximum value is <= t, that means all of the variables are, so
$$P(M \le t) = P(X_1 \le t \text{ and } X_2 \le t \text{ and } \dots X_n \le t)$$
What does independence tell you about how the statement immediately above can be simplified? | {
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} |
mathematics, linear-algebra
&= BZ^jX^iA^T\,\mathrm{tr}_A\left[|\beta_{00}\rangle\langle\beta_{00}\right]\,X^iZ^j \\
&= \frac12BZ^jX^iA^TX^iZ^j
\end{align}\tag1
$$
where we exploited a useful and easy to check property that $(A\otimes I)|\beta_{00}\rangle = (I\otimes A^T)|\beta_{00}\rangle$. We see that if $A$ and $B$ are non-singular, then for the expression $(1)$ to yield the same value for all $i,j$ we need $A$ to commute with $X$ and $Z$. However, any operator $A$ on $\mathbb{C}^2$ can be written as $A=aI+bX+cZ+dXZ$ and it is easy to see that if $A$ commutes with $X$ and $Z$ then $b=c=d=0$. Consequently, $A=aI$.
We conclude that if $A\ne aI$ then $\mathrm{tr}_A((A\otimes B)\rho_{AB})$ is not uniquely defined on the set of density matrices $\rho_{AB}$ with given marginals $\rho_A$ and $\rho_B$. Therefore, no general formula for $\mathrm{tr}_A((A\otimes B)\rho_{AB})$ in terms of $A$, $B$ and the marginals exists. | {
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linux
Originally posted by gvdhoorn with karma: 86574 on 2016-11-20
This answer was ACCEPTED on the original site
Post score: 3 | {
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complexity-theory, turing-machines, nondeterminism
Title: Polynomial time verification of Graph Isomorphism problem Using guess and check method, for two given graphs with the same number of nodes, a NTM selects a permutation of the node set and then checks if the edges are preserved.
The nondeterministic selection of a permutation of the nodes is done in polynomial time.
How is the choice of a function done in polynomial time? This is not clear to me. The choice of function is done in nondeterministic polynomial time which is something you shouldn't try to "make sense of" in the real world.
It is a mathematical model of computing where we assume that the machine can perform many simultaneous operations, kind of in parallel, and if any of these operations "succeed", you get one of those answers out. | {
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"tags": "complexity-theory, turing-machines, nondeterminism",
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ros2
Title: Wrong constructor in ROS2
I am trying to create a constructor for my odom node but for some reason I keep getting the strange error:
error: no matching function for call to ‘rclcpp::TimeSource::TimeSource(<brace-enclosed initializer list>)’
odom_pub{}, _odom_tb{std::make_shared<tf2_ros::StaticTransformBroadcaster>(shared_from_this())}
The thing is that I am not even trying to pass the rclcpp::TimeSource but my compiler thinks so. I think i managed to follow the variable declaration = variable initialization order, so for example in my header:
class OdomNode : public rclcpp::Node
{
private:
int _rate, _ticks_meter, _left_pos, _right_pos, _enc_left, _enc_right, _lmult, _rmult;
int _prev_rencoder, _prev_lencoder;
double _d_left, _d_right;
std::shared_ptr<tf2::Quaternion> q;
std::string _base_frame_id, _odom_frame_id; | {
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t=0:Delta:8;
Lt=length(t);
x1=exp(-a*t);
x2=exp(-b*t);
y=Delta*conv(x1,x2);
y_ac=1/(a-b)*(exp(-b*t)-exp(-a*t));
MSE=sum((y(1:Lt)-y_ac).^2)/Lt
With this code, a time vector t is generated by taking a time interval of Delta for 8 seconds. Convolve the two input signals, x1 and x2, using the function conv. Compute the actual output y_ac using Equation (1). Measure the length of the time vector and input vectors by using the command length(t). The convolution output vector y has a different size (if two input vectors m and n are convolved, the output vector size is m+n-1). Thus, to keep the size the same, use a portion of the output corresponding to y(1:Lt) during the error calculation.
Use a waveform graph to show the waveforms. With the function Build Waveform (Functions → Programming → Waveforms → Build Waveforms), one can show the waveforms across time. Connect the time interval Delta to the input dt of this function to display the waveforms along the time axis (in seconds). | {
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catkin-make
-- Found PythonInterp: /usr/bin/python3 (found suitable version "3.8.5", minimum required is "3")
-- Using PYTHON_EXECUTABLE: /usr/bin/python3
-- Using Debian Python package layout
-- Using empy: /usr/lib/python3/dist-packages/em.py
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/thimo/catkin_ws/build/test_results
-- Forcing gtest/gmock from source, though one was otherwise available.
-- Found gtest sources under '/usr/src/googletest': gtests will be built
-- Found gmock sources under '/usr/src/googletest': gmock will be built
-- Found PythonInterp: /usr/bin/python3 (found version "3.8.5")
-- Using Python nosetests: /usr/bin/nosetests3
-- catkin 0.8.9
-- BUILD_SHARED_LIBS is on
-- BUILD_SHARED_LIBS is on
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- ~~ traversing 1 packages in topological order:
-- ~~ - biosentry_crowd_detection
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | {
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c++, c++17, enum, macros
Title: C++17 enum macro with to_string operator I created a simple enum macro that creates a to_string method for the enum. This has been done before, but my version is designed to compile quickly. From what I can tell, existing libraries use deep preprocessor macros and lots of template instantiations which is taxing for large enums.
Here is the code:
#include <array>
#include <string_view> | {
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ros, sicklms, frequency, laserscan
Originally posted by cybodroid on ROS Answers with karma: 234 on 2016-03-24
Post score: 0
Baud rate does not affect those calculations at all. As @jayess explained in their answer, baud rate is the communication rate on the serial line between the SICK LMS and the PC. The higher the baud rate, the faster the devices communicate, which means there's more bandwidth. When two serial devices communicate, they must both be set to the same baud rate, or else the receiver won't be able to decode the signals it gets. The SICK LMS probably has the baud rate set by a configuration command, so you will have to match the baud rate in your node to whatever your SICK LMS is set to.
Originally posted by Ed Venator with karma: 1185 on 2017-07-13
This answer was ACCEPTED on the original site
Post score: 1 | {
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python, numpy, matplotlib, data-visualization
for ax, y, label, color in zip(fig.axes, ys, labels, colors):
ax.plot(x, y, lw=linewidth, color=color)
ax.text(s=label,
transform=ax.transAxes,
**text_properties)
for ax in ax_rows[:, 0]:
ax.set_ylabel(ylabel)
for ax in ax_rows[-1]:
ax.set_xlabel(xlabel)
return fig
if __name__ == '__main__':
main()
I'm sure that there are other things that could be improved. But this should get you going. | {
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fft, discrete-signals, homework
${x[n]}_{k=0}^{N+K-1}= {d[N − K], d[N − K + 1], . . . , d[N − 1], d[0], d[1], . . . , d[N − 1]}$
$i.e. x[0] = d[N − K], x[1] = d[N − K + 1], . . ..$
At the receiver end, the first $K$ values are discarded and the next $N$ values are saved in a buffer ${y[n]}_{k=0}^{N+K-1}={r[K], r[K + 1], . . . , r[K + N − 1]}, i.e. y[0] = r[K], y[1] =r[K + 1], . . ..$
a) Show that at the receiver end the original data stream d[n] can be recovered
using the following algorithm if the cyclic prefix is sufficiently long. | {
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that provided scientists with concept! Rule so that we can apply the Second Fundamental Theorem of Calculus links these branches... Whose derivative is f, i.e two Fundamental theorems of Calculus, differential and integral Calculus a great of! Theorem of Calculus Definition of the x 2 ) = f ( x.... Antiderivatives previously is the same process as integration ; thus we know that differentiation and integration are inverse.... Integrals to write this integral as a difference of two integrals for which (. *.kastatic.org and *.kasandbox.org are unblocked after the summer holidays and chose math and physics because find. | {
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"url": "http://hosting13059.af9b1.netcup.net/more-preferable-tckrqu/415c7e-fundamental-theorem-of-calculus-part-2-examples"
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c#, algorithm, strings
Title: Algorithm to find substring in a string Can this be improved?
static int find(string term, string text)
{
int found = -1;
int termIndex = 0;
for (int textIndex = 0; textIndex < text.Length; textIndex++)
{
if (term[termIndex] == text[textIndex])
{
if (termIndex == term.Length-1)
return found;
if (termIndex == 0)
found = textIndex;
termIndex++;
}else
{
termIndex = 0;
found = -1;
}
}
return found;
} I do code in C#. I see two problems, one of which was already pointed out:
static int find(string term, string text)
{
int found = -1;
int termIndex = 0;
//quick check to protect the user from themselves
if(String.IsNullOrEmpty(term) || string.IsNullOrEmpty(text))
return -1; | {
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urdf, xacro
<sdf version='1.6'>
<model name='testrobot'>
<link name='base_link'>
<pose frame=''>0 0 0 0 -0 0</pose>
<inertial>
<pose frame=''>0 0 0 0 -0 0</pose>
<mass>1</mass>
<inertia>
<ixx>0.009677</ixx>
<ixy>0</ixy>
<ixz>0</ixz>
<iyy>0.01548</iyy>
<iyz>0</iyz>
<izz>0.009677</izz>
</inertia>
</inertial>
<collision name='base_link_collision'>
<pose frame=''>0 0 0 0 -0 0</pose>
<geometry>
<box>
<size>0.3048 0.3048 0.1524</size>
</box>
</geometry>
<surface>
<bounce>
<restitution_coefficient>0</restitution_coefficient>
<threshold>1e+06</threshold>
</bounce>
<contact>
<collide_without_contact>0</collide_without_contact>
<collide_without_contact_bitmask>1</collide_without_contact_bitmask>
<collide_bitmask>1</collide_bitmask> | {
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ros, navigation, ros-melodic, 2dcostmap, base-local-planner
Originally posted by dpetrini on ROS Answers with karma: 23 on 2020-05-14
Post score: 0
I will answer my own question:
After keep looking for answers and trying many combinations, I discover that is all about syntax.
It seems different versions (using directive "plugins:" or not) eventually requires proper manner to write files.
The solution of my issue above was to write the common_costmap_params.xml file as below:
obstacle_range: 2.5
raytrace_range: 3.0
footprint: [[-0.2,-0.2],[-0.2,0.2], [0.2, 0.2], [0.2,-0.2]]
inflation:
inflation_radius: 0.3
cost_scaling_factor: 50 # exponential rate at which the obstacle cost drops off (default 10)
obstacle_2d_layer:
observation_sources: scan
scan: {data_type: LaserScan, sensor_frame: zed_left_camera_frame, topic: /zed/scan, marking: true, clearing: true, min_obstacle_height: 0.0, max_obstacle_height: 0.5} | {
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ros, gazebo, simulation, sonar
Title: Ultrasonic range sensors in gazebo
Hi, I've been trying to find a robot with at least one ultrasonic range sensor that is already simulated in Gazebo so I can see how it is programmed, but I can't find any, and I see that there isn't a question about this (or I can't find it, of course...)
Thanks in advance!
Miguel.
Originally posted by Capelare on ROS Answers with karma: 202 on 2012-04-24
Post score: 1
Take a look at the reem_common and reem_plugins stacks (they work with ROS Electric). They respectively contain examples of a URDF model with sonars/IRs, and plugins for simulating such sensors in gazebo. HTH.
Originally posted by Adolfo Rodriguez T with karma: 3907 on 2012-04-25
This answer was ACCEPTED on the original site
Post score: 3 | {
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java, security, cryptography, aes
byte[] ibuf = new byte[8192];
int len;
while ((len = in.read(ibuf)) != -1) {
byte[] obuf = ci.update(ibuf, 0, len);
if (obuf != null) {
out.write(obuf);
hmac.update(ibuf, 0, len);
}
}
byte[] obuf = ci.doFinal();
if (obuf != null) {
out.write(obuf);
}
byte[] bmac = hmac.doFinal();
out.write(bmac);
return out.toByteArray();
}
}
}
}
public static String decrypt(byte[] xx, String password) throws Exception { | {
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} |
graph-theory, graph-algorithms, co.combinatorics, optimization, matching
I believe I have a proof that this problem is NP hard (reduction to 3-matching) when I can freely adjust the number of colors, but in the case of two colors, I haven't been able to find anything. I've been searching for the past couple of days for any existing literature on similar problems with no avail. I would appreciate any suggestions or directions in moving forward.
Some ideas I've tested have included reductions to flow/matching problems with disjunctive constraints. | {
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multiplicity of ): The proof is beyond the scope of this course. Let's pull it out of this list, give it a more convenient name, and use it to find a corresponding eigenvector. Now let’s move towards the last topic of this article, that is the algebraic and geometric multiplicity associated with Eigenvalues and Eigenvectors. Ie the eigenspace associated to eigenvalue λ j is $$E(\lambda_{j}) = {x \in V : Ax= \lambda_{j}v}$$ To dimension of eigenspace $$E_{j}$$ is called geometric multiplicity of eigenvalue λ j. eigenvectors respectively, then the are linearly independent. In the example above, 1 has algebraic multiplicity two and geometric multiplicity 1. What is the algebraic multiplicity and geometric. In such cases, a generalized eigenvector of A is a nonzero vector v, which is associated with λ having algebraic multiplicity k ≥1, satisfying. Furthermore, an eigenvalue's geometric multiplicity cannot exceed its algebraic multiplicity. Algebraic & Geometric multiplicity of | {
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"url": "http://zlpt.bjoy.pw/algebraic-and-geometric-multiplicity-of-eigenvectors.html"
} |
electricity, electric-current, measurements, instrument, scales
a voltage across a resistance that object's equilibrium temperature is not linear in the applied voltage. For instance, assuming the wire's primary mode of heat transfer is radiative, the magnitude of power loss is given by | {
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java, strings, array, haskell, parsing
private static boolean evaluate(String left, String op, String right)
{
switch (op)
{
case "==":
return left.equals(right);
case "!=":
return !left.equals(right);
default:
System.err.println("ERROR: Operator type not recognized.");
return false;
}
}
} You've written something quite impressive there, but it is an unorthodox
approach and some of the code is rather impenetrable. I've laid out a few
points of issue and in some cases possible solutions and comments below.
Method documentation
Your methods could stand to have a brief JavaDoc block at the top. Here's how
you might annotate what I believe to be your simplest method, isInt:
/**
* Determines whether a given string consists only of digits.
*
* @param s The string to test.
* @return True if the string consists only of digits; false otherwise.
*/ | {
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c++, c++11, tree, binary-search
};
int main()
{
BinaryTree<int> bt1;
bt1.insertValue(100);
bt1.insertValue(20);
bt1.insertValue(30);
bt1.insertValue(400);
bt1.insertValue(50);
std::cout << "In Order: ";
bt1.print_inOrder();
std::cout<<"\n";
std::cout << "Pre Order: ";
bt1.print_preOrder();
std::cout<<"\n";
std::cout << "Post Order: ";
bt1.print_postOrder();
std::cout << "\nDeleting 20 ";
bt1.deleteValue(20);
std::cout<<"\n";
std::cout << "In Order: ";
bt1.print_inOrder();
std::cout<<"\n";
std::cout << "Pre Order: ";
bt1.print_preOrder();
std::cout<<"\n";
std::cout << "Post Order: ";
bt1.print_postOrder();
} The other answer makes some excellent suggestions. I won't repeat them here.
You have a bug in insertValue
You don't have any checks to make sure that a value is not inserted twice.
If I use
bt1.insertValue(20);
bt1.insertValue(20); | {
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#### "Don't panic!"
Well, yes in general, but a section of the tangent bundle would be a vector field, not a tangent space. Consider the general bundle charts for a point.
Sorry, I meant to put fibre, not section (was just about to change it, but you beat me).
Would it be correct to say that one could add a vector from a tangent space at one point to a vector from a tangent space at another point, but this will in general not correspond to tangent vector in either space - it will not be tangent to any curves passing through either point?
Also, from another point of view could one argue that adding the two vectors component wise relies on choosing a basis and is this clearly coordinate dependent, hence such an operation has no geometrical meaning - the resulting vector will not be in the tangent bundle over the manifold?!
Sorry to labour the point, I don't know why I'm finding it so hard to conceptualise.
Last edited: | {
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"url": "https://www.physicsforums.com/threads/tangent-spaces-at-different-points-on-a-manifold.845373/"
} |
# Balls and Urns with Two Color Balls
In how many ways can we place 7 identical red balls and 7 identical blue balls into 5 distinct urns if each urn has at least 1 ball?
This is how I approached the problem:
1) Compute the number of total combinations if there were no constraints:
Placing just the red balls, allowing for empty urns: $$\binom{n+k-1}{k-1} = \binom{7+5-1}{5-1} = \binom{11}{4} = 330$$. There are the same number of blue ball configurations.
Since each red ball configuration can have 330 possible blue ball configurations, then in total we should have $$330^2 = 108900$$
2) Compute the number of illegal configurations with 1, 2, 3 or 4 empty urns: | {
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"url": "https://math.stackexchange.com/questions/3531809/balls-and-urns-with-two-color-balls"
} |
ros
roslaunch: No definition of [python-yaml] for OS version []
camera_calibration_parsers: No definition of [yaml-cpp] for OS version []
rqt_publisher: No definition of [python-rospkg] for OS version []
roswtf: No definition of [python-rospkg] for OS version []
geometric_shapes: No definition of [boost] for OS version []
stage_ros: No definition of [boost] for OS version []
rqt_robot_steering: No definition of [python-rospkg] for OS version []
rqt_web: No definition of [python-rospkg] for OS version []
genpy: No definition of [python-yaml] for OS version []
roslisp: No definition of [boost] for OS version []
message_filters: No definition of [boost] for OS version []
rosmake: No definition of [python-rospkg] for OS version []
rosbag: No definition of [python-rospkg] for OS version []
rqt_shell: No definition of [python-rospkg] for OS version []
rostime: No definition of [boost] for OS version []
roscreate: No definition of [python-rospkg] for OS version [] | {
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c#, performance, beginner, error-handling, tcp
//methods:
public bool Connect(string IP, int port)
{
try
{
bool successFlag = false;
lock (syncLock)
{
try
{
client = new TcpClient();
client.Connect(IP, port);
client.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true); | {
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"url": null
} |
c++, image, mathematics, graphics
enum class Orientation {
X_POS,
X_NEG,
Y_POS,
Y_NEG,
Z_POS,
Z_NEG
};
// using simple 3d rotation matrices:
// X_POS and X_NEG rotate by -90 and 90 around y.
// Y_POS and Y_NEG rotate by 90 and -90 around x.
// Z_POS rotates by 180 around y and Z_NEG doesn't rotate.
Vector rotate(const Vector& v, const Orientation o) {
switch (o) {
case Orientation::X_POS:
return Vector{ -v.z, v.y, v.x };
case Orientation::X_NEG:
return Vector{ v.z, v.y, -v.x };
case Orientation::Y_POS:
return Vector{ v.x, v.z, -v.y };
case Orientation::Y_NEG:
return Vector{ v.x, -v.z, v.y };
case Orientation::Z_POS:
return Vector{ -v.x, v.y, -v.z };
case Orientation::Z_NEG:
return Vector{ v.x, v.y, v.z };
default:
assert(false);
return Vector{ 0.0, 0.0, 0.0 };
}
}
class SphericalImage {
public:
std::vector<unsigned char> data;
int width, height, nchannels; | {
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} |
stringWithDistance f;
while ((f = q.poll()) != null) {
if (f.candidateString.equals(t)) {
return f.distance;
}
for (int i = 0; i < str.length(); ++i) {
String strStart = i == 0 ? "" : str.substring(0, i);
String strEnd = i + 1 < str.length() ? str.substring(i + 1) : "";
for (int c = 0; c < 26; ++c) {
String modStr = strStart + (char)('a' + c) + strEnd;
if (visited.contains(modStr)) {
visited.remove(modStr);
}
}
}
}
I'm having a hard time understanding why this algorithm is $O(n^2)$. I know that the time complexity of processing the vertices/words is $O(n)$, but based on the text I'm reading, processing the edges in the worst case would be $O(n^2)$, so we would have $O(n + n^2)$, giving us $O(n^2)$.
I just can't see how that is taking place. The second loop is a constant (right?), it doesn't change with the size of $n$, so I don't think that is a part of the calculation for the run time.
Any help would be greatly appreciated. | {
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"openwebmath_score": 0.5871614813804626,
"tags": null,
"url": "https://cs.stackexchange.com/questions/94236/time-complexity-of-transforming-one-string-to-another"
} |
mysql, database
Title: Entity Relationship Diagram for Grade Calculator I was wondering if anyone would be able to review my Grade Calculator for a course ERD? I'm looking for ways to improve the current design (if any improvements need to be made that is) and if anyone could review the current MySQL query which is there. In order for this to be reviewed I was told I needed an SQL query to accompany it. | {
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c#, beginner
because I find it easier to quickly see what is happening but we are getting into coding convention wars here and this point is heavily A Matter Of Personal Preference [AMOPP (tm)]
As @Hosch250 says above always put in the braces in if/else blocks. I have seen a LOT of errors along the lines of
if (something)
DoThis();
DoThat();
where the intent is only to DoThat() if something is true.
The only place I don't use the braces (see AMOPP (tm) above) is simple control statements and they are deliberately formatted to indicate that they are the only statement invoked.
if(something) then break;
// or
if(_value == value) then return
Game Design
The game is hardcoded to be between 1 and 100. This could easily be parameterised in the constructor.
public class GuessingGame
{
private readonly int _initialLowerBound;
private readonly int _initialUpperBound; | {
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fft
Title: Prepare data for FFT I'm reading the various FFT algorithms and the input consists usually of real and imaginary parts.
The real data can be for example an audio input and the imaginary part should be the same sized array filled with zeros. But the algorithm, for example the bit reverse part works also on the imaginary part, essentially moving zeros around. What's the point in it? If you're using the usual Decimation-In-Time Cooley-Tukey radix-2 FFT, the buffer of samples going in need to be scrambled in order by having the indices of the samples bit-reversed. And if the FFT is a complex-input, complex-output FFT and it is given real data, yes the imaginary part is set to zero.
And, in the case of a purely real input signal, you need not bother swapping those imaginary parts in your data preparation before passing to the net FFT algorithm expecting the input to be in bit-reversed order. But you do have to bother with the real parts of the samples. | {
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fl.formal-languages, context-free
Indeed, let's consider an arbitrary word of the type $(a^m b)^n$ from the language $L$ (here, $m$ and $n$ don't have to be equal). It necessarily has $m \geqslant 1$ and $n \geqslant 2$.
An arbitrary word from $L$ looks like $w_1 w_2 \ldots w_d a^{2t + 1} b$, where $d \geqslant 1$, $t \geqslant 0$ and all the words $w_i$ are in the language $K$. Hence, if the word $(a^m b)^n$ is in $L$, then $w_1 = a^m b a^{m/2}$ (and $m$ has to be even), $w_2 = a^{m/2} ba^{m/4}$, $w_3 = a^{3m/4} ba^{3m/8}$, $\ldots$, $w_d = a^{m \cdot p_d / 2^{d-1}} b a^{m \cdot p_d / 2^d}$. Here, $p_1$, $p_2$, $\ldots$, $p_d$ are the numerators of the fractions that appear in the definitions of $w_i$. For example, $p_1 = 1, p_2 = 1, p_3 = 3, p_4 = 5, p_5 = 11$, et cetera. It can be proven via induction that all $p_i$'s are odd. Moreover, $p_i / 2^{i-1}$ and $p_i / 2^i$ are successive binary approximations of $2/3$ and $1/3$ respectively (but this is not important here). | {
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students may not be prepared for the equation for exponential decay, discussion of half-life and radioactive decay prepares entry-level students for the introduction of more mathematical discussion of exponential growth and decay in upper level classes. 28311, t1 -30. These can be recognizable by those functions with a base which is between and. y = 32x Base = 2 Exponential growth y- intercept (x=0) = 3 x y = 3 Base = Exponential Decay y- intercept (x=0) = 3 MODELING: We use the concept of exponential growth in the real world: Ex: Since 2005, the amount of money spent at restaurants in the U. 0 4 are fixed so the function is exponential. 1An initial population of 910 armadillos increases at an annual rate of 5%. Continuous Growth/Decay, Continuously Compounding Interest, etc. Finding an exponential function given its graph. Exponential Growth and Decay Word Problems Write an equation for each situation and answer the question. a) Is this a growth or decay model?. Exponential Functions | {
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c++, sorting, heap
fill_vector() is a curious interface. I would expect get_random_data() which returns the vector.
Know your operators. ++i, i <= num_of_elems is equivalent to ++i <= num_elements.
Anyway, that should be a for-loop, or you could omit i and just count the argument down to zero.
Kudos for using constexpr to avoid preprocessor-cnstants where not needed. Still, ALL_CAPS_AND_UNDERSCORES identifiers are generally reserved for preprocessor-macros. They warn/assure everyone that preprocessor-rules apply. Fix the naming too.
The C++ headers <cxxx> modelled on the C headers <xxx.h> only guarantee to put their symbols into ::std. Don't assume they are also in the global namespace.
max_heap() will often try to create pointers far beyond the passed range. Creating such a pointer invokes undefined behavior.
For simple and correct code, better use indices. | {
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c#, linq, entity-framework
var employees = query.AsEnumerable();
var offices = _officeService.GetAllOffices();
var employeeData = from e in employees
join o in offices on e.Office equals o.Code
select new EmployeeData
{
EmployeeId = e.EmployeeId,
FullName = e.FullName,
Office = e.Office,
Area = o.Area,
Region = o.Region,
OfficeName = o.Name,
Position = e.Position,
Languages = e.Languages
};
return employeeData; The dilemmas here: | {
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organic-chemistry, nomenclature
(…), the first criterion to be considered in choosing a preferred parent acyclic chain is the length of the chain; unsaturation is now the second criterion.
If your book is still using old nomenclature rules, it would expect the other answer A to be correct. | {
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astrophysics, atmospheric-science, sun, cosmic-rays, solar-wind
A and C are when the Sun undergoes CMEs, and B and D are when particles from those CMEs reach Earth. Both lead to Forbush decreases, although the second is more dramatic, as is the spike preceding it (likely from SEPs).
On a larger scale, of course, there is indeed a correlation between the solar cycle and cosmic ray detection:
This happens for much the same reasons as the Forbush decreases. The above chart, by the way, matches very well the observations recorded in the graph you specified: | {
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supplementary. Note: ∠ APD and ∠ CPB are not adjacent to each other, because they don’t have a common arm in spite of having a common vertex. A pair of adjacent angles formed by intersecting lines is called a Linear Pair of Angles. Obviously, the larger angle ∠BAD is the sum of the two adjacent angles. If two angles are not adjacent, then they do not form a linear pair. They are supplementary because each angle is 90 degrees so they add up to 180 degrees. A linear pair of angles is formed when two lines intersect. To identify whether the angles are adjacent or not, we must remember its basic properties that are … How to Find Adjacent Angles. Draw a pair of vertically opposite angles. They also share a common vertex (point A). , ∠1 and ∠3 are non-adjacent angles that angles of the linear which. And a straight angle the two lines intersect opposite angles are not adjacent:! Angle adjacent angles which are not in a linear pair is the common vertex and edge but do not form a linear pair, | {
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ros, roslisp
I note that line 31 of make-host-1.sh appears to be
$SBCL_XC_HOST < make-host-1.lisp || exit 1
I may be completely mistaken, but am guessing that may imply that something, I don't know what, upstream in the build process is setting the environment variable SBCL_XC_HOST to 'sbcl', but that that executable, if it exists at all, is not in my PATH at that point.
Am I correct in believing I need to build roslisp_support from source in order to use Roslisp? If so, does anyone have any advice on how to get it built successfully?
Originally posted by dfm on ROS Answers with karma: 26 on 2013-07-30
Post score: 0
I think I've figured this one out.
Before you can build and install SBCL, you have to install SBCL. :-)
That's not quite as silly as it sounds. The following recipe worked for me. Start with
sudo apt-get install sbcl | {
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homework-and-exercises, electromagnetism
We need to show: $\nabla\times\iiint\frac{\nabla'\times\vec{E}(\vec{r'})}{|\vec{r}-\vec{r'}|}d^{3}r'=-\frac{\partial\vec{A}}{\partial t}$.
We can use Faraday's law, take the time derivative out, and the spatial curl into the integral.
We then use: $\nabla\times\varphi\vec{F}=\nabla\varphi\times\vec{F}+\varphi\nabla\times\vec{F}$, and take $\nabla'=-\nabla$ on the scalar term $\frac{1}{|\vec{r}-\vec{r'}|}$ | {
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np-complete, np-hard, satisfiability, decision-problem
Title: Solving SAT correctly on all but $poly(m)$ formulas The question is to show that there is no deterministic polynomial time algorithm that solves SAT correctly on all but $poly(m)$ formulas of size $m$, for every $m \geq 0$ unless $P \ne NP$.
I know that if $P = NP$, a polynomial time algorithm exists that, given a Boolean formula φ, actually produces a satisfying assignment for φ if it is satisfiable. But I can't really understand how a poly time algorithm can solve SAT correctly on only $poly(m)$ formulas, if $P \neq NP$. Am I missing something in understanding the problem or there is a catch? I'll provide a sketch.
Given any formula $\varphi$ of size $m$, we can rewrite it in an equisatisfiable way as $\varphi \land p$ where $p$ is a fresh propositional variable. In this way, we can generate an infinite amount of equisatisfiable formulas. | {
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electrostatics, statistical-mechanics, voltage, electrochemistry
Title: In the Volta potential or Nernst potential equations, where does the logarithm come from? In both Volta potential and Nernst potential equations, besides some constants, temperature and valence parameters, the potential is a function of the logarithm of the ratio of two densities (or concentrations).
I have a problem understanding why a logarithm.
In the ideal gas law, pressure difference is linearly proportional to the number of moles, so a differential (e.g. transmembrane) pressure is linearly proportional to the substraction of the two compartments number of moles, not a log of their ratio.
So this must have to do, I guess, with the fundamental difference between a voltage and a pressure. A voltage is joule per coulomb, a pressure is (among other SI definitions) joule per cubic meter. Since coulomb force adds another pressure of some kind on top of the motion of particles and it has a longer range than collisions, this could be why. | {
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newtonian-mechanics, classical-mechanics, forces
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
The force between two particles in electromagnetism can violate this. For a concrete example consider a positive charged particle A pulled along the x axis at a constant velocity in the positive direction, and another positive charged particle B pulled along the y axis at a constant velocity in the positive direction. If it is arranged such that when A is at (0,0), B is at (0,1), then we can calculate the fields and find:
the electric forces on the particles will be in opposing directions
the magnetic force on A is zero
the magnetic force on B is in the -x direction
Does this mean momentum is not conserved here? No.
If we include the person or device pulling these charges along as part of the system (so there are no external forces), then we should expect the momentum of the system to be conserved. | {
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algorithms, algorithm-analysis, recurrence-relation, recursion, pseudocode
$$U(1) = 0$$
$$U(n) = 1 + U(n-1), \text { for } n\gt 1$$
Notice the first "1" in the last equality, which stands for the call to FACTORIAL with parameter $n-1$ in the code, n * FACTORIAL(n-1) while $U(n-1)$ comes from the number of recursive calls made by FACTORIAL(n-1). In other words, the recursive calls made by FACTORIAL(n-1) does not include that call itself, which is, though of course, counted towards the recursive calls made by FACTORIAL(n). We can also check by contradiction. Let us suppose we did not have that "1". Then we would get $U(4)=U(3)=U(2)=U(1)=0$, which said that we had made no recursive calls to FACTORIAL when we had computed FACTORIAL(4), which is not true at all.
In the same way as in this simple example, all those constant 1's and one 2 in the question come from right where the calls are made. For example, when x = 2, the function will return (3*RANDOM(n-1) + RANDOM(n-1) + 1), which incurs $(1+R(n-1)) + (1+ R(n-1)) = 2 + 2*R(n-1)$ recursive calls. | {
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ros, pr2, image-transport, video, extract-images
Originally posted by wmcmahan on ROS Answers with karma: 70 on 2011-07-05
Post score: 0
I once made a small video_to_bag and a bag_to_video package, it's on our git it is not optimal yet, it could use some timing and camera calibration extension, so patches are highly appreciated! But perhaps it is suitable for your task.
Originally posted by KoenBuys with karma: 2314 on 2011-07-05
This answer was ACCEPTED on the original site
Post score: 1 | {
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javascript, mithril.js
function doStuff() {
alert(foo.bar)
}
}
This style avoids issues with this scoping and makes it easier to scan the public signature of the controller.
When using m.route, I recommend that you bind to document.body instead of document, so that you can put stylesheets in <head> and take advantage of the browser downloading/rendering optimizations.
Other than those, the code looks fairly well organized. The views are well written, and the code is easy to read, overall. | {
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c++, performance, algorithm, recursion, io
I considered adding a check for n=1 since that would leave only one possibility for the last character, saving some recursive calls, but that would add another if to be called in every function call, either.
What more ways are there to improve the speed? Any improvements are not bound to C++, I will take a look at every programming language which might be more efficient in this case, though I guess there scarcely will be one.
The algorithm:
#include <iostream>
#include <vector>
#include <bits/stdc++.h>
#include <cstdio> | {
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organic-chemistry, aromatic-compounds, synthesis
Title: How to convert benzene to 1-bromo-3-iodobenzene? Today, my chemistry teacher gave the following organic conversion as homework: benzene to 1-bromo-3-iodobenzene.
I tried something like:
I am not sure about it, can someone review my conversion (as I have got an exam tomorrow)? It looks pretty good overall. The order of substitution is correct to achieve the required pattern but there are two points I would pick up on.
The final substitution of the diazonium salt is best done with $\ce{CuI}$ rather than $\ce{KI}$ as the copper(I) ions catalyse the reaction. Also heating is not required; the reaction can be run at room temperature (or possible slightly above but not much).
The diazonium salt is drawn incorrectly since it is ionic in nature. There is a triple bond between the nitrogens and a formal positive charge on the middle nitrogen, although in reality the charge is delocalised over both atoms: | {
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quantum-mechanics, hilbert-space, operators, non-locality
The problem is that if you go beyond allowing single derivatives into allowing multiple derivatives, then you start allowing information from more and more points far away from the point of interest, and at some point things get unreasonable. Moreover, there isn't a clear line where things get unreasonable, so the placement of that line (including whether it includes single derivatives or not) is a subjective matter. | {
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machine-learning, predictive-modeling, model-selection
Title: How would you describe the trade-off between model interpretability and model prediction power in layman's terms? I know it depends on the data and question asked but imagine a scenario that for a given dataset you could either go for a fairly complex nonlinear model (hard to interpret though) giving you a better prediction power perhaps because the model may see the nonlinearities present in the data, or have a simple model (perhaps a linear model or something) with less prediction power but easier to interpret. Here is a very good post discussing ideas on how to interpret machine learning models.
Industries, while being very cautious, are slowly becoming more interested in adopting more complex models! Still they want to know the trade-off clearly? A data scientist perhaps is the one sitting between data team and decision-makers, and often need to be able to explain these stuffs in layman's terms. | {
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thermodynamics, radiation
Yes, for instance, if radiation from A is focused on B, while radiation from B is directed elsewhere. The relevant statement of the second law of thermodynamics says:
Heat can never pass from a colder to a warmer body without some other
change, connected therewith, occurring at the same time.
While heat is transferred from A to B, B is radiating into universe, which should cause "other changes". So, there is no violation of the second law of thermodynamics.
In particular if A reflects the wavelengths that B is emitting the
radiation at would this be possible?
Yes, it is possible. It could be viewed as a variation of the first scenario.
And if so is this process independent of the temperature of B (since A
is reflective) or does A radiate as a function of the temperature
difference with its surroundings (in this case B). | {
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$$\Gamma\left(\frac{1}{6}\right) = \color{red}{\frac{2^{\frac{14}{9}}\cdot 3^{\frac{1}{3}}\cdot \pi^{\frac{5}{6}} }{\text{AGM}\left(1+\sqrt{3},\sqrt{8}\right)^{\frac{2}{3}}}}.$$
The last identity was missing in the Wikipedia page about particular values of the $\Gamma$ function, so I took the liberty to add it and add this answer as a reference. | {
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navigation, move-base, ros-kinetic
-Publish the desired path using the package you have.
-Subscribe to the published path in your robot's control system.
-Extract the necessary path information from the received message.
-Implement a control algorithm that interprets the path information and generates appropriate commands for the robot.
-Execute the control commands in your robot's hardware or simulation environment.
Basically, you have three options. | {
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python, parsing, xml, iteration, lxml
Output looks like this (as it should, there is no leeway regarding its structure): | {
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general-relativity, lagrangian-formalism, differential-geometry, variational-principle, boundary-terms
$$I_{EH} + I_{GHY} = \frac{1}{2 \kappa^2} \int_{M}d^{d+1}x \sqrt{-g} R + \frac{1}{\kappa^2} \int_{\partial M} d^{d}x \sqrt{-h} K ~.$$
The metric on $M$ is $g_{\mu\nu}$, and $R = g^{\mu\nu} R_{\mu\nu}$ is the Ricci Scalar. The induced metric on the boundary $\partial M$ is $h_{\mu\nu} = g_{\mu\nu} - n_{\mu} n_{\nu}$, where $n^{\mu}$ is the (spacelike) unit vector normal to $\partial M \subset M$. Now consider a small variation in the metric: $g_{\mu\nu} \to g_{\mu\nu} + \delta g_{\mu\nu}$. The quantities appearing in the Einstein-Hilbert part of the action change in the following manner:
$$ \delta \sqrt{-g} = \frac{1}{2} \sqrt{-g} g^{\mu\nu} \delta g_{\mu\nu}$$
$$ \delta R = -R^{\mu\nu} \delta g_{\mu\nu} + \nabla^{\mu}\left(\nabla^{\nu} \delta g_{\mu\nu} - g^{\nu\lambda} \nabla_{\mu} \delta g_{\nu\lambda} \right)$$
Thus, the change in $I_{EH}$ is | {
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electricity
Title: Electron flow in Cathode Ray Tube? Electron flow in Cathode Ray Tube?
In a TV CRT, electrons from the cathode go pass the anode and strike the TV screen to produce the picture. It seems that, in order to for the system to work, the electrons hitting the screen must be redirected back to the anode to complete the electrical circuit.
I'll like to known how such a circuit is actually done in a CRT. In the big cathode ray tubes that used to be used in television receivers, the inside of the glass walls leading up to the screen were coated with graphite, and the coat connected to the eht (extra high tension) supply, whose other end was (directly or indirectly) connected to the cathode, so that electrons landing on the screen were returned to source. I believe that in an oscilloscope tube (are they still made?), there's enough natural conductance through the inner glass surface for electrons to find their way back. | {
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n - 1 /5 = 2.577 distribution formula is given –. By subtracting the mean of the sample data set the standard deviation is a measure of the difference each... Mean value of the difference between each value and the sample data set is an array of numbers S. / n - 1 mean of the sample standard deviation formula between each value and the sample mean and µ than,. ) /5 = 2.577 from each value: 1 - 4 = -3 / 5 = 20/5.. Deviations are found by subtracting the mean is ( 1 + 2 + 4 + 5 + 8 ) 5. The sample and population is represented as σ ͞x and σ as σ and... = sample standard deviation is a measure of the sample and population is as... Sampling distribution formula is S = sample standard deviation sample standard deviation we are in! Size of more than 30, the mean is ( 1 + 2 + +... Scores within a set of data sample standard deviation, the mean from value! Given below – here, the mean of the difference between each value: 1 - 4 =.. 1 + 2 + 4 + 5 + 8 ) / 5 = 20/5 =4 ( 12.96 2.56! Mean value of | {
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homework-and-exercises
I now wish to generate a second curve, one that shows the irradiance at the earth's surface. I know that the scattering and absorption processes that take place in the atmosphere not only reduce the intensity but also change the spectral distribution of the direct solar beam.
I want to show the spectral distribution of solar irradiance at seal level for a Zenith sun and a clear sky. So, the curve that I want to show is the spectral distribution as it would be if there were scattering but no absorption. For this I would also like to make the assumption that the solar elevation is more than 30 degrees.
Does anyone know how I could produce the curve explained above? This is getting complicated. :) You have to make a lot of assumptions to make progress; you have listed most of them. I'll explicitly add an assumption that we consider only Rayleigh scattering (more-or-less consistent with "clear sky"), and that the atmosphere is pure N${}_2$. | {
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ros
Title: How I completely remove all ros from my system?
Hello,
The ros path and different versions of ros couses problem in my system.
I want to completely uninstall ros from my system. I want to completely remove all things related to ros from my system. How can I done this?
Then wan't to install a fresh ROS
Originally posted by unais on ROS Answers with karma: 313 on 2013-03-05
Post score: 18
If you're running Ubuntu, and installed ROS with apt-get, the first step would be
sudo apt-get remove ros-*
If you've created a workspace, you'll have to also remove that... and if you added the setup scripts to your .bashrc, you'd have to remove them too.
If you've installed from source then it will be more complicated.
Originally posted by Jon Stephan with karma: 837 on 2013-03-05
This answer was ACCEPTED on the original site
Post score: 39 | {
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training, neuroevolution
Title: Emergent behavior in AI models that looks similar to natural neural systems "ImageNet Classification with Deep Convolutional Neural Networks" by Krizhevsky & Sutskever & Hinton describes very interesting emergent behavior of the AlexNet.
It was trained on 2 GPU's:
specialization exhibited by the two GPUs ... The kernels on GPU 1 are largely color-agnostic, while the kernels on on GPU 2 are largely color-specific. This kind of specialization occurs during every run and is independent of any particular random weight initialization | {
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mechanical-engineering, pulleys
what you get from the equilibrium is $4F = 48[N]$.
I hope that is sufficient as an explanation, I tend to find that problems with pulleys can have different configurations and as such it is always better to turn to the basics. | {
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optics, visible-light, interference, diffraction
Things to note:
The more diagonal, the greater the frequency of these colour oscillations
The more vertical, the more colourful/vibrant the pattern
The more horizontal, the more black/white/grayscale the pattern
The variation in the frequency of the colour oscillation on a given strand is due to the curvature in the hair. If I hold it perfectly straight with a second hand, there is no oscillation at all, but a single, pure colour, the entire length.
My screen is the matte, 1920 by 1080px, IPS screen of the Dell XPS 13. If I zoom in on it with a clip-on macro phone lens, this is what I see: | {
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"tags": "optics, visible-light, interference, diffraction",
"url": null
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waves, acoustics
(p\vec A) \cdot d\vec x \\ &= p (\vec A \cdot d\vec x) = p\,dV.
\end{align} The work per unit area is
$$
\frac{dW}A = p
\frac{dV}{A} = p\,dx,
$$
where $dx$ is again the displacement of the
surface. Then the power per unit area is
$$
\frac{dP}{A} =
\frac{dW}{A\,dt} = p\frac{dx}{dt} = pv,
$$
where $v=dx/dt$ is the
speed of the surface.
It doesn't feel like too much of a stretch to say that the direction
of the energy transfer will be in the direction of the velocity of the
surface, as well.
To see that this treatment works for sound waves, imagine
one-dimensional sound waves moving left-to-right in a pipe. (Image
source) | {
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newtonian-mechanics, classical-mechanics, orbital-motion
The integral for $t(r)$ is
$$t=\int_{r_0}^r\frac{dr}{\sqrt{\frac{2E}{m}-\frac{2k}{mr}-\frac{L^2}{m^2 r^2}}}$$
where $E$ is the conserved energy (positive), $L$ is the conserved angular momentum (either positive or negative), and $k$ is the constant for the potential, $V(r)=k/r$ (which is positive for a repulsive inverse-square force).
We can rewrite this as
$$Ct=\int_{r_0}^r\frac{r\,dr}{\sqrt{r^2-2Ar-B^2}}$$
where $A=k/2E$, $B=L/\sqrt{2mE}$, and $C=\sqrt{2E/m}$; $A$, $B^2$, and $C$ are all positive constants.
As you've found, a brute-force integration produces a mess, so the trick is to change variables to make the integral look nicer.
Let $$r=A+\sqrt{A^2+B^2}\cosh\eta.$$ Then the integral becomes
$$Ct=\int_{\eta_0}^\eta(A+\sqrt{A^2+B^2}\cosh\eta)\,d\eta$$
so
$$Ct=A\eta+\sqrt{A^2+B^2}\sinh\eta$$
Thus $r(\eta)$ and $t(\eta)$ are simple formulas giving a nice parameterization of $r(t)$ in terms of a parameter $\eta$.
You can invert $r(\eta)$ to get | {
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To leverage this we have:
Any compact CW complex $$X$$ embeds in $$D^n$$ for some $$n\in\mathbb{N}$$. If $$X$$ is contractible, then it is a retract of $$D^n$$.
In fact every locally-finite CW complex of dimension $$n$$ embeds in $$\mathbb{R}^{2n+1}$$ as a neighbourhood retract (see Fritsch, Piccinini, Cellular Structures in Topology Th.1.5.15). Of course every compact CW complex is finite-dimensional, and has bounded image under the previous embedding. That a finite complex should be a retract of any disc in which it embeds is a consequence of Paul's answer here.
Now, in light of the previous two observations we use Brouwer's fixed point theorem to conclude the following.
Every compact CW complex (triangulable or not) which is contractible has the fixed-point propety. $$\square$$
Of course the full machinery is more powerful, and has application outside the realm of CW complexes. | {
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quantum-mechanics, thermodynamics, statistical-mechanics, terminology, gas
Title: Why are hydrogen, helium and neon known as quantum gases in the mid-20th-century chemical literature? So, while reading over equations of states, I learned that quantum gases do not conform to the same corresponding state behavior as normal fluids do.
Why are these known as quantum gases and why do they not conform to the same corresponding state behavior as normal fluid?
One example of this language, appearing in Introduction To Chemical Engineering Thermodynamics by JM Smith, is as follows: | {
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lagrangian-formalism, nuclear-physics, representation-theory, group-representations, isospin-symmetry
In my understanding ( which may be wrong and then should be corrected) the construction of the invariant Lagrangian follows from building inside the two representation spaces $D_1$ and $D_{1/2} $ invariants from both the doublet and the triplet.
In the D1/2 representation we have as an invariant the term $ \psi ^T \psi$, where $\psi$ stands for the doublet and T for the dagger symbol.
My problems comes when I have to mix this term with the triplet $ \phi$ of the pions in the D1 repr. If I just take the term $\psi ^T \psi $ and put it as it is in the D1 rep and multiply it by $ \phi $ I surely don' t have an invariant( taking that the quantity \psi ^T \psi remains in the same form?).
What I have seen in practice is that one should take the term $\Phi = \tau _k \phi ^k $, and then construct the invariant as $L_{int} = \psi ^T \Phi \psi = \psi ^T \phi _k \tau ^k \psi .$ $\tau $ are the Pauli matrices in 2x2 form as generators of the group SU(2).
Question: | {
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electromagnetism, magnetic-fields, electric-fields, electricity, field-theory
of $\mathbf{H}$); $\mathbf{B}$ depends on the specific materials you used and even, if iron is present, on the history of your magnet. On the other hand, if you want to set up an electric field, you do not plaster a known free charge on the plates of a parallel plate capacitor; rather, you connect them to a battery of known voltage. It's the potential difference you read on your dial, and that determines $\mathbf{E}$ (or rather, the line integral of $\mathbf{E}$); $\mathbf{D}$ depends on the details of the dielectric you're using. If it were easy to measure charge, and hard to measure potential, then you'd find experimentalists talking about $\mathbf{D}$ instead of $\mathbf{E}$. So the relative familiarity of $\mathbf{H}$, as contrasted with $\mathbf{D}$, derives from purely practical considerations; theoretically, they're on an equal footing. Many authors call $\mathbf{H}$, not $\mathbf{B}$, the "magnetic field". Then they have to invent a new word for $\mathbf{B}$: the "flux | {
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newtonian-gravity
But for an object with very large mass(big stars, black holes), the gravity can be a trillion times greater than that of earth or maybe even more. | {
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Given given 5 points $\mathbf{a},\mathbf{b},\mathbf{c},\mathbf{d},\mathbf{e},$ take the line through the centroid of the triangle determined by some three which is in the direction of the sum of the other two. There are ten ways to do this. CLAIM: all ten meet at a common point.
Proof: one way is the line through the point $$\mathbf{q}=\frac13(\mathbf{a}+\mathbf{b}+\mathbf{c})$$ in the direction of the vector $\mathbf{d}+\mathbf{e}.$ The general point on this line has the form $$\mathbf{q}+t(\mathbf{d}+\mathbf{e})=\frac13(\mathbf{a}+\mathbf{b}+\mathbf{c})+t(\mathbf{d}+\mathbf{e}).$$ The other $9$ lines are similar with some other partition of the $5$ points. Clearly, the choice $t=\frac13$ shows that the point $$\mathbf{p}=\frac{\mathbf{a}+\mathbf{b}+\mathbf{c}+\mathbf{d}+\mathbf{e}}{3}$$ is on all $10$ lines. | {
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"url": "https://mathoverflow.net/questions/188485/ten-concurrent-lines"
} |
vba, outlook
appStartDate = myAppt.Start
appStartTime = myAppt.Start
appEndDate = myAppt.End
appEndTime = myAppt.End | {
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gazebo, c++
Title: ROS Answers SE migration: c++ api gazebo
Hi, i'm new in Ros.
I want to see a example of a program in c++ where i can see how i can move the joints.
I'm a beginner, so i can't know how I can find thiys information.
Thank you
Angelo
Originally posted by manang on ROS Answers with karma: 1 on 2012-02-28
Post score: 1
You can use the ros libraries and plugins. You add a controller in gazebo which listens to a topic, e.g. gazebo_ros_force. For your case you might want to use gazebo_ros_p3d, to change the position instead of force.
Add a controller to your urdf file like so:
<controller:gazebo_ros_force name="controller_name" plugin="libgazebo_ros_force.so">
<alwaysOn>true</alwaysOn>
<updateRate>1000.0</updateRate>
<topicName>force1</topicName>
<bodyName>body_name</bodyName>
</controller:gazebo_ros_force> | {
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newtonian-mechanics, momentum, conservation-laws, projectile, everyday-life
but even THAT equation doesn't even apply in the case of the baseball strike since there is a human being providing a force EVEN as the bat hits the ball.
I know this is ingrained deeply in the minds of physics students because we have conservation of momentum drilled into our heads as young students in introductory physics, but I encourage everyone to always think intuitively about physics scenarios before applying equations.
Anyways, I hope that was valuable. Cheers! Yes. Consider throwing a ball at a bat which is held stationary: the ball is momentarily stationary but at all other times it is moving faster than the bat.
Now consider sweeping the bat towards an initially stationary ball: if the ball is not to stick to the bat, then it must be moving faster than it when it loses contact with it. (This case is identical to the one above with a different choice of reference frame of course.) | {
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java, performance, multithreading, thread-safety
The fact, that this is synchronous code smells. You call one method, that joins the queue, battle and returns results of the game. Is very likely to be bad in real life. I see getting results more like asynchronous callback called in the end for both players. It also gets rid of the second infinite loop that you have there.
For me this seems like ideal case for producer-consumer scenario. It deals with all of the problems I described above. You can have multiple producers (game clients) and single consumer that handles game ("server"). Whenever a player wants to join, he will be added to player queue and battles will be handled by consumer, that will always require 2 players. This will also clearly separate code, that handles players waiting to join and players that are starting the game. Then you can for example do some kind of matchmaking and match players together based on their rating easily by choosing how to take player pairs from the current queue. | {
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