constexpr auto operator*(matrix_type<S1> m1, matrix_type<S2> m2) {
auto storage = fmap(
[=](auto row) {
return zip_with(
scalar_prod,
repeat_n(m2.ncolumns(), row),
columns(m2));
}
, rows(m1));
return matrix_type<decltype(storage)>{storage};
}
