sub kronecker_product {
    my ($x, $y) = @_;

    return $x-> dummy( 0 )
             -> dummy( 0 )
             -> mult( $y, 0 )
             -> clump( 0, 2 )
             -> clump( 1, 2 )
}

##</code><code>##

use PDL::NiceSlice;

sub kronecker_product {
    my ($x, $y) = @_;

    ( $x( *1, *1 ) * $y )
        -> clump( 0, 2 )
        -> clump( 1, 2 )
}