Why do the random numbers repeat in each run?
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Hi, I have the following issue. I see that when I run this function to generate a number of perturbations num_perm to a given array solution.position. This function is part of a more extensive code. The issue is that when I run the function I get a repeated output and it should be random. I add the rng('shuffle') function and I do get different values in each execution. I have used the randi and randsample functions and the behavior is the same. What could be going on, I usually get the random solution without adding any rng options. When I run the same code in Octave I do get random solution.position.
function [solution, f] = INITIAL_PERTURBATION(solution, num_perm, FA)
r = 1;
while (r <= num_perm)
% r1 = randi([1 FA - 1]);
% r2 = randi([2 FA]);
sample = randsample(FA, 2);
r1 = sample(1);
r2 = sample(2);
if ~isequal(r1, r2)
fprintf(' \n Generating initial solution... %d \n ', r)
% Apply permutations to positions and concentrations arrays
new_position = SWAP(solution.position, r1, r2);
new_concentration_array = SWAP(solution.concentration_array, r1, r2);
% Check contiguous fresh fuel assemblies
U238 = 20.53285;
[~, idxcol] = find(new_concentration_array == U238);
fresh_assemblies = idxcol'; % ########
t = CHECK_CONTIGUOUS_ASSEMBLIES(fresh_assemblies);
if t == 1
continue;
else
solution.position = new_position;
solution.concentration_array = new_concentration_array;
f = fresh_assemblies;
r = r + 1;
end
end
end
Thanks in advance. Kind regards.
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采纳的回答
Walter Roberson
2022-3-25
When you use randi() each value is determined independently of the others.
For example
HT = 'HT';
HT(randi(2, 1, 5))
If, hypothetically, it was not possible for randi to repeat values, then at most two values could be output and it would either have to be 'HT' or 'TH' .
randperm() on the other hand cannot output duplicates within one call . It is completely permitted to output duplicates across different calls.
6 个评论
Walter Roberson
2022-3-25
MATLAB initializes with rng('default')
Initializes Mersenne Twister generator with seed 0. This is the default setting at the start of each MATLAB session.
So if you do not change the random number seed, then each MATLAB session would start out with exactly the same pattern of random numbers.
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