a note on band matrix arithmetic band matrix is square band width is a number of diagonals wich contain numbers band width is always odd (1 main diag + m lower diags + m upper diags) so for a matrix N by N there can be a maximum of (2*n - 1) diagonals (in this case it is an ordinary dense matrix with all diags filled) only equally sized matrices can be involved in operations (+-*) operations on band matrices yield band matrices +- operations on two matrices with bandwidths w1 and w2 evidently yield a band matrix with width = max(w1, w2) multiplication of w1 and w2 widths matrices yields a matrix with width = (w1 + w2 - 1) so i guess there must be a specialization for handling such cases and more: a band matrix can be also symmetric (i don't know yet if this is redundant) -- Pavel