sub p{$t=pdl+pop;for(@_){
  my $a=outer$t,pdl+pop;
  transpose($a);
  my $n=-1+nelem$t;
  $t=zeroes($n*2+1);
  $t->slice("$_:".($_+$n))+=$a->slice("$_,:")for 0..$n;
}
[list$t]}