Array elements that are members of set.
tf = specfun_ismember ( a , s )
a ma-by-na matrix
a 1-by-ns matrix
a ma-by-na matrix of booleans, tf(i,j) is %t if there is an entry in s matching a(i,j).
Search in a the entries which are in s.
Uses vectorized statements, based on the Kronecker product. The intermediate memory required is ma*na*ns.