if ismember(P,A) == ones(1,length(P)) && ismember(P,D) ~= ones(1,length(D))
P is a vector. ismember() is going to return a vector the same length. == comparison to ones is going to return a vector the same length. You cannot use && with vectors
You could perhaps replace the first test with
if all(ismember(P, A))
Your second test is harder to make sense of as your documentation does not make clear what you want to have happen if some entries match but others do not. I seem to be having difficulty translating your documentation as to what the program is intended to do or how it is intended to do it.
My guess:
if all(ismember(P, A)) && ~any(ismember(P, D))
