creating positive definite matrix using wishrnd in matlab

Question

I used the below code to create a matrix of wishart distribution,

clc
sigma =eye(100); df=2;mu=zeros(100,1);
wishart_matrix=wishart_distribution(sigma,df)
normal_vector=mvnrnd(mu,inv(w1),1);

function W=wishart_distribution(sigma,df)
W = wishrnd(sigma,df);
end

function G = gauss_distribution(mu, sigma,count)
 rng default  % For reproducibility
 G = mvnrnd(mu,sigma,count);
end

I encountered the below error, it seems inv(sigma) is not positive semi-definite matrix, how can i fix it?

Error using mvnrnd (line 110)
SIGMA must be a symmetric positive semi-definite matrix.

Error in sahar_vbssm>gauss_distribution (line 323)
G = mvnrnd(mu,sigma,count);

Answer 1

To generate a random positive definite matrix in MATLAB, use

a = rand(3,3)
ata = a'*a