Questions tagged [sampling]

Creating samples from a well-specified population using a probabilistic method and/or producing random numbers from a specified distribution.

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35 views

Quota sampling participants

We need to select participants, based on the quotas provided. For example: exactly 15 men exactly 15 women exactly 10 young exactly 10 middle aged exactly 10 old exactly 10 poor exactly 10 middle ...
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1answer
32 views

Algorithm for selecting a sample that's as spread out as possible?

I have a large database of data with dates. There are large gaps and large chunks of data without gaps. I want to get a sample of this data such that the dates are as spread out as possible (i.e. as ...
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58 views

Peculiar MCMC sampling problem

I have two random variables, X and Y, and Y is a positive real number. I can sample from $p(y|x)$, but I need to sample from $p(x)$, which I know to be proportional to $\frac 1 {E[y|x]}$. I could ...
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1answer
68 views

Generate random matrix and its inverse

I want to randomly generate a pair of invertible matrices $A,B$ that are inverses of each other. In other words, I want to sample uniformly at random from the set of pairs $A,B$ of matrices such that ...
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12 views

Raters and subsampling

In order to select questions for an online contest, we get contributors to submit potential questions that they write themselves. Then, out of, say 100 submitted questions, we have to rate them and ...
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1answer
39 views

Sampling in large graph using simple random walk

I'm studying sampling techniques in online social networks. The assumption is we don't have full access to the network(i.e, we don’t know the size of the network). However crawling is supported, i.e, ...
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1answer
46 views

Sampling numbers from a weighted set that sum to constant value

So I have a multi-set of positive integers $S = \{n_1, n_2, \dots\}$ with associated weights $W = \{w_1, w_2, \dots\}$. I want to sample some numbers, without replacement, from $S$ according to ...
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2answers
90 views

Efficient n-choose-k random sampling

Is there an efficient method of sampling an n-choose-k combination at random (with uniform probability, for example)? I have read this question but it asks for generations of all combinations, not ...
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61 views

Complexity of generating non-uniform random variates

What can we say about the complexity of generating (negative) binomial and (negative) hypergeometric random variates? In particular, it is possible to generate (negative) binomial and (negative) ...
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2answers
982 views

Sampling perfect matching uniformly at random

Suppose I have a graph $G$ with $M(G)$ the (unknown) set of perfect matchings of $G$. Suppose this set is non-empty, then how difficult is it to sample uniformly at random from $M(G)$? What if I am ...
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3answers
2k views

Random sampling in a polygon

I would like to sample a uniformly random point in a polygon... If sample a large number they'd be equally likely to fall into two regions if they have the same area. This would be quite simple if ...
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2answers
129 views

Efficiently shuffling items in $N$ buckets using $O(N)$ space

I’ve run into a challenging algorithm puzzle while trying to generate a large amount of test data. The problem is as follows: We have $N$ buckets, $B_1$ through $B_N$. Each bucket $B_i$ maps to a ...
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2answers
57 views

Nyquist theorem, sample meaning

Given that this wave was sampled at a sampling frequency f: Why does the wave sampled at a sampling frequency 3f/2 look like this? What does 3f/2 mean? Does it mean that we sample every 2 waves 3 ...
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1answer
55 views

Sample K representative frames within a video

I have an image-based processing module that takes photos for some computer vision processing. I have many videos, but I need to sample representative frames as its inputs, preferably those frames ...
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1answer
193 views

Proof Knuth S algortihm correctness

In the programming pearls book by Jon Bentley, there is a section about the problem of finding a random set of m integers from range 0 to n-1 integers. To do so they use Knuth's algorithm given by the ...
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2answers
70 views

Fast sampling from discrete space

Assume we are given a set $X = \{x_1,...,x_n \}$ of size $n$, and a probability distribution $P$ over $X$. I am interested in an algorithm $A$ which can sample from $X$ according to $P$, i.e. $\Pr(A=...
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49 views

L1 sampling for sampling edges of a graph

I am trying to sample the edges of an undirected graph using weights. The goal is to run a sparsification algorithm on the graph. I see the point that L1 norm is best for sparsification. Can someone ...
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1answer
511 views

How to use Latin hypercube sampling with fixed points?

I use Latin hypercube sampling to select what point to evaluate my function. As evaluations take a lot of time, I want to limit the time by adding already evaluated points. I thought about taking the ...
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1answer
62 views

Uniform sampling with constraints

Suppose one wants to uniformly sample a string $w$ of a given length over a finite alphabet, such $w$ satisfies a set of structural constraints (such as - "the third character has to be equal to the ...
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0answers
305 views

Backward mapping with bilinear sampler

I have some experiences with Convolutional Neural Networks before. I have a question regarding the Bilinear Sampler used in "Unsupervised Monocular Depth Estimation With Left-Right Consistency" (the ...
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1answer
23 views

Testing two distributions, both accept null hypothesis

I have a sample that is collected to verify the accuracy of a new random number generator. Applying the goodness of fit test to check if this sample comes from the Standard Normal Distribution and ...
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2answers
53 views

Limit repetitions in randomized list with each unique element occurring n times

I have a set of 3 elements and need to generate a randomized sequence containing each element n times with the condition that one element can only occur m times in a row. So with elements [0,1,2] n = ...
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0answers
35 views

Constrained selection of a random sample from a set of items with multiple attributes

Suppose I have a collection of N items, each of which has A different attributes, a1, a2, ..., aA. Attribute ai can take on Vi different possible (discrete) values, distributed across the population ...
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302 views

Generate a Random Diagonally Dominant Matrix

I would like to write a function to generate a diagonally dominant matrix of random values. What I'm ultimately leading to is writing a code to implement the Jacobi method on this matrix in CUDA for a ...
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4answers
8k views

Uniform sampling from a simplex

I am looking for an algorithm to generate an array of N random numbers, such that the sum of the N numbers is 1, and all numbers lie within 0 and 1. For example, N=3, the random point (x, y, z) should ...
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1answer
36 views

Randomly choose a line - algorithm

We have a large file that can't fit into internal memory. How do we randomly pick one line so that each line has the same probability to be picked? And how do we randomly pick such n lines so that ...
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3answers
1k views

How to select a binary tree node uniformly at random

The exercise I'm trying to solve is You are implementing a binary search tree class from scratch, which, in addition, to insert, find and delete, has a method ...
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3answers
13k views

Why is the Mersenne Twister regarded as good?

The Mersenne Twister is widely regarded as good. Heck, the CPython source says that it "is one of the most extensively tested generators in existence." But what does this mean? When asked to list ...
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1answer
258 views

Bilinear Interpolation

I am trying to implement bilinear interpolation as described in the paper Spatial Tranformer Networks by Jaderberg et. al (see link to paper). They describe bilinear interpolation in Equation 5 as: $$...
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39 views

What is the relationship between entropy rate and quantization?

I have a totally random source of signal data that looks like a typical normal distribution. I've included an image as I like pictures:- The source has a mean of 0, and a standard deviation of 1. ...
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0answers
60 views

Strength-based player cards sampling [closed]

Let's say we have a card game, like poker. Inputs are board cards and an array of cards strength(that is calculated based on the board cards and game rules). For example for 3 ranks(A, K, Q) /2 ...
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3answers
415 views

Why do we need Gibbs sampling (and MCMC)?

I just learned about Gibbs Sampling which is an MCMC method. Given a distribution $\pi$, we want to sample an item according to $\pi$. Maybe my alternative suggestion would sound somewhat naive (even ...
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9answers
15k views

How to simulate a die given a fair coin

Suppose that you're given a fair coin and you would like to simulate the probability distribution of repeatedly flipping a fair (six-sided) die. My initial idea is that we need to choose appropriate ...
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1answer
60 views

Finding the (probable) maximum of a large set of integers *without* iterating over all of the values

As in the title, I am trying to find the largest (aka least upper bound) of a (very large) set of integers. Importantly, I do not have direct access to the full list of integers, but I do have a ...
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1answer
28 views

Sampling among constrained partitions

I'm working on a clustering problem and want to sample partitions (possible clustering solutions) among a set of constrained ones. Here is the problem: I have a set of objects $O=\{o_1,\ldots,o_n\}$ ...
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1answer
65 views

Sampling from a set of numbers with a fixed sum

Let $s = \{x_1, x_2, \ldots, x_n\}$ be a set of $n$ random non-negative integers where $\sum_i x_i = n$. And let $\{y_1, y_2, \ldots, y_{\sqrt{n}}\}$ denote a subset of size $\sqrt{n}$ of $s$, chosen ...
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1answer
6k views

Generate scale-free networks with power-law degree distributions using Barabasi-Albert

I'm trying to reproduce the synthetic networks (graphs) described in some papers. It is stated that the Barabasi-Albert model was used to create "scale-free networks with power-law degree ...
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1answer
507 views

Randomly select a uniform subsample from a nonuniform dataset

I have a dataset of events with timestamps spanning several months. The event rate is "bursty", i.e. there are periods of much higher and lower rate than the average. I would like to randomly select ...
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3answers
3k views

What's a uniform shuffle?

What does it mean exactly a "uniform shuffle" algorithm ? Is this method considered a uniform shuffle ? ...
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1answer
24 views

What do the terms 'Sample' and 'Sampling' mean in the discussion of Pattern Recognition and Machine Learning?

The tag sampling tells me that, Creating samples from a well-specified population using a probabilistic method and/or producing random numbers from a specified distribution. Now, the question ...
4
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1answer
108 views

Uniformly sampling from cycles of a graph

I was wondering if, given an arbitrary cycle basis (that's complete, e.g. every cycle in the graph can be expressed as the $\mathbb{Z}/2\mathbb{Z}$ sum of elements from the basis) of some graph $G$, ...
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0answers
92 views

Uniform sampling from general simplex with a twist [closed]

This is part of a question I had asked elsewhere, and then some of the links redirected me to CS stack exchange. Given $a_1,\dots,a_D$ (all strictly positive), I want to draw points uniformly from ...
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0answers
239 views

Uniform generation of random bipartite bi-regular graphs?

I want an algorithm that takes the following Input: $M,N,k,d$ positive integers such that $kM = dN$. and produces the following Output: Random bipartite graph, with $M$ vertices all of degree $k$ ...
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1answer
109 views

How broken is LCG in the case of partial output?

Suppose we have a linear congruential generator defined by $X_{n+1} = (a X_n + c) \mod 2^n$ where $a, c, n$ are all known and we would like to determine the initial value $X_0$. However, if we can ...
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3answers
203 views

Efficiently generating a uniformly random list of unique integers in a range

The problem: To generate a list of size $n$, Containing unique integers, Sampled uniformly in the range $\left[0,m\right)$, In $O(n)$ time, except that: Assuming $m$ is bounded by some word-size, $\...
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2answers
88 views

Random sampling of tuples

When I talked with students about pseudo-random number generation, I mentioned that you should not blindly use subsequent outputs of a pseudo-random number generator (PRNG) to form tuples as they may ...
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1answer
756 views

Generate a random graph with geometrical degree distribution

I'm working on graph generation, trying to implement the RT-nested-Smallworld network model described in this paper. We are talking about generating an undirected graph in a slightly different way ...
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3answers
244 views

Is there a random shuffle algorithm using only true /false?

Is there a way to randomly shuffle an array using only a source of random boolean values? SO to clarify, shuffle using true /false only, and not integers or decimals. For this question, I'm ...
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3answers
1k views

Best random permutation employing only one random number

The ideal random permutation algorithm of Fisher and Yates (Algorithm P in Knuth vol.2) for a sequence of $n$ objects requires $n-1$ random numbers. In some card games one first does a "cut" and ...
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232 views

Linear regression - iterative approach

I have a single output variable $y$ and a number of inputs $x_1$, $x_2$, etc. These are time series. Each $x_i$ explains the changes in $y$ in specific circumstances, and the goal is to have a linear ...