How to find location of parameters in a genarized matrix

I want to find the location of tunable parameters within a generalized matrix.

I want to make sure I don't miss parameters with values set to zero, so converting to double won't work.

Is this possible?

For example:

p = realp('p', 0);
A = genmat(zeros(5));
A(2,4) = p;

% now find the location of p in A