MATLAB: How to index a random matrix with set conditions

Question

How can I find elements within a random matrix M (5×5) that are negative or are between 20 and 40?

Answer 1

For a list of the negative values:

negM = M(M<0)

For the indices of the negative values:

[i,j] = find(M<0)

To display only the negative values in a matrix:

N = M;
N(N>=0) = 0

For values between 20 and 40

values = M(M>=20 & M<=40)