Hi, here's the demo: <hansl> loop for (i=2; i>=1; i--) matrix m = I(i) m[diag] = ones(i) print i m[1:i, 1:i][diag] = ones(i) # fails (only) for i==1 endloop </hansl> I suspect that m[1:i, 1:i] is internally treated as scalar and/or that diag doesn't work with the scalar type. My wish would be that x[diag] for a scalar just refers to (returns) the scalar itself. thanks sven