MATLAB: Problem with using randsample

random number gene...random number generatorrandom selectionrandsample

Hi, I have a set that its members change in a loop and I want to select just one member of it randomly and evaluate the result. the written code is as below:

CandidateNode = randsample(UnvisitedNode,1);

it works good but sometimes its result is not acceptable. for example when UnvisitedNode=[3] running this code have different result. sometimes CandidateNode=[1], sometimes CandidateNode=[2] and sometimes CandidateNode=[3] how could I fix it? tanx in advanced

Best Answer

When the first parameter of randsample is a single number k, the assumption is that you want a random sample from the integers 1:k. It looks like you will have to check numel(UnvisitedNode) and return its value when numel=1.

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MATLAB: How can we generate random numbers between two negative values.

a = -5 ;
b = -1.670000000000000 ; 
r = (b-a).*rand(1000,1) + a;

MATLAB: Seed choise in rng.

The choice of seed value is arbitrary. It's not like a seed of 42 would make the array of pseudorandom numbers generated by the next call to rand / randn / randi / randperm "more random" or "less random" than a seed of 43. If you set the seed using rng to the same value and call the same random number function to generate the same number of pseudorandom numbers you'll get the same set of numbers.

rng(42)
x1 = rand(1, 10);
rng(42)
x2 = rand(1, 10);
isequal(x1, x2) % true

For your additional question, if exprnd calls rand, randn, randi, and/or randperm in the same order and with the same inputs each time you call it and doesn't change the random number stream inside itself (by calling rng or by explicitly creating a random number stream for its own use) yes, you can get reproducible results from exprnd. Looking at the exprnd code, it calls rand and performs a few computations using the numbers returned from that call. It doesn't change the random number stream inside.

rng(12345)
x1 = exprnd(0.5, 1, 10);
rng(12345)
x2 = exprnd(0.5, 1, 10);
isequal(x1, x2)

Note the advice at the end of the "Specify the Seed" section on this documentation page. This can insulate you from legacy code that uses discouraged syntaxes of rand and randn.

Best Answer

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MATLAB: How can we generate random numbers between two negative values.

MATLAB: Seed choise in rng.

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