function Jan29()

n = 100;
A = sprand(n,n,.2);
[i,j,s] = find(A);
i = [i i+n];
j = [j j+n];
s = [s s];
B = sparse(i,j,s);
spy(B)
shg
% Idea:
% If 1<=i<=n and 1<=j<=n  then B(i,j) = B(i+n,j+n) = A(i,j).