I am not certain what you are asking.
If you want to add different uniform random numbers with a minimum value of 1 and a maximum value of 3 to every element in ‘A’, you have to tell the unifrnd function to create a matrix the size of ‘A’.
Try this:
A=[1,2;2,4];
[r,c] = size(A);
uniform_test=unifrnd(1,3,r,c); % Random Matrix (Size Of ‘A’)
Anew = A + uniform_test
