finding and storing non zero elements in a NxN matrix

Hi, I would like to know how i can determine the non zero elements in a matrix consisting mostly of zeros and store its matrix coordinate positions. So in a 64*64 matrix i can determine the non zero elements by making a for loop like this for ix=1:n

       for iy=1:n

           if newpositions(ix,iy)==0

               %nah u alrite

           else

               newpsi(ix,iy)=%%%here i want to store the ix and iy elements in an array instead of storing them in a huge ix*iy matrix

           end

       end

   end

Answer 1

[José-Luis]

 doc sparse

Answer 2

[Jos (10584)]

help find

M = rand(5) < 0.2 ; % some data
[r,c,v] = find(M) ; % row and column indices of non-zero elements (with values v)