use warnings;
use strict;
use PDL;
use PDL::NiceSlice;
use Test::PDL 'eq_pdl', 
              -tolerance => 0.42;

my $mask = zeroes 7,7,3;
$mask( pdl( 0..2, 4..6 ), 4, 0:2 ) .= 1;
$mask( 4, pdl( 0..2, 4..6 ), 0:2 ) .= 1;

my $good_matrix = random 7,7,3;
my $some_matrix;
my $count;

while () {
    $some_matrix = random 7,7,3;
    last if eq_pdl $good_matrix * $mask,
                   $some_matrix * $mask;
    $count ++
}

$PDL::doubleformat = '%.1f';

print "it worked only after $count attempts,\n",
      "mask was: $mask",
      "good matrix was: $good_matrix",
      "and it was not very different from: $some_matrix";