Generate Random Matrix in Matlab

Question

Is there any way in Matlab to generate a 5000 x 1000 matrix of random numbers in which:

MM = betarnd(A,B,1,1000);

but A and B are vectors (1 x 5000). I get the following error message:

??? Error using ==> betarnd at 29
Size information is inconsistent.

I want to avoid a loop like the following one:

for ii = 1 : 1000
  MM(:,ii) = betarnd(A,B); 
end

Thanks!

@madbitloman I assume because there are 5000 different values — Luis Mendo
– Luis Mendo, Commented Apr 10, 2015 at 21:08
From your code I think you want a 1000x5000 matrix, not 5000x1000. Right? — Luis Mendo
– Luis Mendo, Commented Apr 10, 2015 at 21:13
hi there, thanks for the answers. @madbitloman, yes, I need the 5000 values because I need to sample that much pdfs. Luis, yes you're right. As I wrote it, it should be 1000x5000. — Oliver Amundsen
– Oliver Amundsen, Commented Apr 12, 2015 at 1:52

Luis Mendo · Accepted Answer · 2015-04-10 21:20:31Z

1

You can repeat A and B (vectors of size 1x5000) to obtain matrices of size 1000x5000 in which all rows are equal, and use those matrices as inputs to betarnd. That way you get a result of size 1000x5000 in which column k contains 1000 random values with parameters A(k) and B(k).

The reason is that, according to the documentation (emphasis mine):

R = betarnd(A,B) returns an array of random numbers chosen from the beta distribution with parameters A and B. The size of R is the common size of A and B if both are arrays.

So, use

MM = betarnd(repmat(A(:).',1000,1), repmat(B(:).',1000,1));

edited Apr 10, 2015 at 21:20

answered Apr 10, 2015 at 21:15

Luis Mendo

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2 Comments

Oliver Amundsen Over a year ago

nice and clean. Thanks Luis!

Luis Mendo Over a year ago

@OliverAmundsen Great! I wasn't sure whether that was what you needed

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