Generating Pseudo Random Numbers in MATLAB

I wrote the code found in this post in the Student Version of MATLAB R2009a (7.8.0.347) on Windows Vista SP2.

function U = js_randv(i, x)
%js_randv Pseudo Random Number Vector Generator
% Returns a pseudo random number vector
% according to congruential random number generator
%   i = length of vector
%   x = seed value of sequence
%   U = vector of Xi+1 = (a * Xi) mod m

isFirst = 0;

a = 16807;          % 7^5 predetermined multiplicative value
m = 2147483647;     % 2^31-1 predetermined prime number
r = 2836;           % m div a
q = 127773;         % m mod a
T = zeros(1, i);    % holds seed values
U = zeros(1, i);    % holds returned uniform random numbers in (0,1)

% loop through all indices of vector
for j=1:i
    % if this is the first value, use seed
    if isFirst == 0
        seed = (a * mod(x, q)) - (r * (x / q));
        T(1, j) = seed;
        isFirst = 1;
    % if this is not the first value, use current index
    else
        previousValue = T(1, j-1);
        seed = (a * mod(previousValue, q)) - (r * (previousValue / q));
        T(1, j) = seed;
    end

	U(1, j) = seed / m;
end
end

function U = js_randv(i, x)

%js_randv Pseudo Random Number Vector Generator

% Returns a pseudo random number vector

% according to congruential random number generator

% i = length of vector

% x = seed value of sequence

% U = vector of Xi+1 = (a * Xi) mod m

isFirst = 0;

a = 16807; % 7^5 predetermined multiplicative value

m = 2147483647; % 2^31-1 predetermined prime number

r = 2836; % m div a

q = 127773; % m mod a

T = zeros(1, i); % holds seed values

U = zeros(1, i); % holds returned uniform random numbers in (0,1)

% loop through all indices of vector

for j=1:i

% if this is the first value, use seed

if isFirst == 0

seed = (a * mod(x, q)) - (r * (x / q));

T(1, j) = seed;

isFirst = 1;

% if this is not the first value, use current index

else

previousValue = T(1, j-1);

seed = (a * mod(previousValue, q)) - (r * (previousValue / q));

T(1, j) = seed;

end

U(1, j) = seed / m;

end

This function will return a vector of size i containing randomly generated numbers uniformly distributed between 0 and 1. It’s not perfect, but it got the job done. I’ll get around to explaining it more beyond the meager comments another time.

References:
Generating Random Numbers
Linear congruential generator

4 thoughts on “Generating Pseudo Random Numbers in MATLAB”

Hi!

My name is Anna and I want to thank you for posting this code, I need to modify the code for a project digital image processing, where I need a pseudo random noise sequence and researching I came to this was reduced to generate a sequence of random numbers . The particularity of the noise I create is that I should only have values between -1, 0 and 1 and then there’s my mission. Thank you very much again!

Sorry for my bad English 😛

Hi Anna. What type of distribution are you trying to generate these numbers under? Uniform, random, etc. See: http://www.mathworks.com/access/helpdesk/help/techdoc/ref/rand.html for an easy way to generate matrices of uniformly distributed numbers and http://www.mathworks.com/access/helpdesk/help/techdoc/ref/randn.html for normally distributed numbers.

My method of generating random numbers is a bit cumbersome, but seemed to work for my application. It may not work for yours. Good luck!

My method of generating random numbers is a bit cumbersome, but seemed to work for my application. It may not work for yours ?

Free ?

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4 thoughts on “Generating Pseudo Random Numbers in MATLAB”

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