Questions tagged [random-sampling]

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2answers
194 views

Different questions about “Inverse Physics problems”

I am in a context of forecasts in astrophysics. Don't be too rude if questions seem to you stupid or naive but rather indulgent, I am just looking for better undertsand all these numerical methods of ...
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0answers
30 views

Name of method for quickly sampling many small-probability booleans

I have a list of probabilities $p_k$, each corresponding to a Bernoulli distribution. These values of $p_k$ are all small (let's say 0.1% or less). I want to prepare a data structure that allows ...
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3answers
254 views

Generating Random Orthogonal Matrices in C++

I'm looking for an open-source library for the generation of random n-dimensional orthogonal matrices in C++. In python, it looks like such a function is available in the NumPy package. But I was not ...
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1answer
37 views

How is the D value being updated at simple RRT algorithm?

I am studying the following lecture (image) regarding 5 iterations of the simple RRT algorithm. I am trying to understand how each value is being updated regarding each iteration. I have figured out ...
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1answer
75 views

Monte Carlo - Random Walk Simulation - polyfit the log log data points?

This is part of the code in matlab for a random-walk simulation. To test the code, I'm using steps=[30]; there will be more values, but I want to run it for 1 trial to decrease code processing. <...
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1answer
62 views

Is there a better way to do run time analysis than this?

I currently have 2 different functions with options to vectorise them: acc_rej_sine(max_iter, algorithm=None) and ...
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0answers
31 views

Randomized Submatrix of a Sparse Matrix

I have a sparse square matrix $A$ with size $n \times n$ and number of nonzero entries $nnz$. The goal is making a sub-matrix $B$ with $s$ nonzeros which are randomly chosen from $A$. Duplicates are ...
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2answers
1k views

Uniform dots distribution in a sphere

I'm trying to implement Barnes-Hut algorithm, with a binary tree. My initial conditions are a uniform mass distribution in a sphere with radius $R$. How can I create uniform dots distribution in a ...
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1answer
106 views

Sampling simulation steps logarithmically

The common case of for instance a Monte Carlo simulation is, if we want to run our simulation for $N$ steps, we define a delta $\Delta,$ such that $N/\Delta = n$ tells us the frequency with which we ...
3
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1answer
51 views

Testing Wiener process splitting in adaptive-step SDE integrators

I am investigating various methods for adaptive-step integration of stochastic differential equations and trying to implement them. All of the papers that I've seen (e.g. H. Lamba, J. Comp. App. Math. ...
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4answers
1k views

Rotate a vector by a randomly oriented angle

We start off with a unit vector $\mathbf{v}$ randomly oriented in 3D space and we want to generate another unit vector $\mathbf{w}$ so that $$ \mathbf{w}\cdot \mathbf{v} = \cos \beta $$ where $\beta$...
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2answers
930 views

Estimate information entropy through Monte Carlo sampling

I am looking for methods that allow estimating the information entropy of a distribution when the only practical ways of sampling from that distribution are Monte Carlo methods. My problem is not ...
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1answer
148 views

Why are Hamiltonian dynamics used in MCMC?

In Hamiltonian Monte Carlo, Hamiltonian dynamics are used to generate new proposals from the current state. I understand why these dynamics are used as opposed to random walk behavior to generate ...
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1answer
50 views

Finding optimal point distance to get desired number of random points in an area

I have a random point generator which takes a distance $d$ and fills an area with points such that distance between any two points is no less that $d$: I need to control the number of points in the ...
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2answers
50 views

How to choose a good distribution for visualizing phase changes in the nature of the roots of a quadratic equation

I'm not sure if this SE site is the best one for this question, so let me know where it should be moved to if you think it doesn't belong here. After learning about the quadratic formula, I'm ...
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1answer
415 views

(numpy/scipy) Build a random vector given mean vector and covariance matrix

After running several calculations with numpy, I end with the mean vector and covariance matrix for a state vector. Is there a way with numpy or scipy to sample a random vector around this mean and ...
2
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1answer
55 views

Sampling vector so they will have a given euclidean distances matrix

Given a matrix $M\in\mathbb{R}^{P\times P}$ , is it possible to sample $P$ vectors $u_i\in\mathbb{R}^N$, $i=1..P$ so that $\|u_i-u_j\|=M_{ij}$. Obviously for not any $M$ this is possible, i.e. it has ...
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3answers
769 views

How to sample points in hyperbolic space?

Hyperbolic space in the Poincaré upper half space model looks like ordinary $\Bbb R^n$ but with the notion of angle and distance distorted in a relatively simple way. In Euclidean space I can sample a ...
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0answers
74 views

Monte Carlo sampling of particle system for velocity dependent potential

When sampling configurations of point particles in statistical mechanics by means of (Markov chain) Monte Carlo, we may work with a potential that only depends on the positions of the particles, and ...
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5answers
1k views

Algorithm for efficient weighted sampling from a collection that can efficiently be updated

I'm writing a Monte Carlo simulation in which I have to maintain a large collection of items. This collection contains a great many duplicates, and it will most likely be best to store some or all of ...
2
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1answer
131 views

What is the name of the optimization algorithm that uses random sampling?

I am generating random weight as per e.g. below. The I generate a set of 3 values say 100, 250, 300 and I multiple them with the weights below Initial population. ...
3
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1answer
295 views

Random placement of euclidean points with constrained inter-point distances in a fixed area

I'd like to place as many random points as possible in a 2D square $S=[0,1]x[0,1]$ such that the euclidean distance $d$ between any two points $d$ is greater than a given value $b$ (b is small). I'm ...
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1answer
911 views

Sampling from posterior predictive distribution

First post. I'm working on this problem using Bayesian methods. In desperation I'm considering using p-values (shock horror), specifically posterior predictive p-values. So I need to simulate from the ...