Help Storing Values in a Matrix For Loop

I know this questions has been asked numerous times, but I haven't found an answer for this case. It is hard to explain so, I will put the code in to hopefully help better understand the problem.

red_matrix=zeros(5)

for ii=2
    matrix_sort=sort(time(:))
    n=[2:25]
    min_t(ii)=matrix_sort(n(ii));%new min t after initialization
   [row(ii),col(ii)]=find(time==min_t(ii));%finding block address
   red_matrix(row(ii),col(ii))=1

so after every loop, there is a different column and row that needs to be replaced with a "1" in the red_matrix. The problem is, that I need to keep the old 1 value also. I've tried everything I can think of but it keeps resetting the matrix after every loop.