sub do_matrix(\@) {
    my( $avMatrix )= @_;
    my( $rows )= 0+@$avMatrix;
    my( $cols )= 0+@{$avMatrix->[0]};
    my $in= pack "d*", map @$_[0..$cols-1], @$avMatrix;
    my $out= pack "d".($rows*$rows);
    _do_matrix( $in, $rows, $cols, $out );
    my @out= unpack "d*", $out;
    my @ret;
    while(  @out  ) {
        push @ret, [ splice( @out, 0, $rows ) ];
    }
    return \@ret;
}