use warnings;
use strict;
use PDL;
use PDL::NiceSlice;

#fancy matrix
#set to a blank 3d test matrix

my $matrix = zeroes 7,7,3;

#set some values for matrix

$matrix( pdl( 0..2, 4..6 ), 4, 0:2 ) .= 1;
$matrix( 4, pdl( 0..2, 4..6 ), 0:2 ) .= 1;

#the conditional problem child

my $ind = $matrix-> whichND( $matrix == 1 );

if ( all $matrix-> indexND( $ind ) == 1 ) {
    print "it worked\n";
}

##</code><code>##

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";

##</code><code>##

it worked only after 144532 attempts,
mask was: 
[
 [
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 0 0 0]
  [1 1 1 0 1 1 1]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
 ]
 [
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 0 0 0]
  [1 1 1 0 1 1 1]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
 ]
 [
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
  [0 0 0 0 0 0 0]
  [1 1 1 0 1 1 1]
  [0 0 0 0 1 0 0]
  [0 0 0 0 1 0 0]
 ]
]
good matrix was: 
[
 [
  [0.4 0.3 0.3 0.9 0.6 0.3 0.2]
  [0.8 0.8 0.2 0.8 0.6 0.9 0.2]
  [0.9 0.0 1.0 0.3 0.8 1.0 0.3]
  [0.5 0.3 0.8 0.5 0.3 0.6 1.0]
  [0.8 0.7 0.3 0.4 0.3 0.2 0.4]
  [1.0 0.4 0.8 0.9 0.4 0.2 0.9]
  [0.0 0.8 0.7 0.9 0.0 0.1 0.7]
 ]
 [
  [0.1 0.8 0.5 1.0 0.5 0.1 0.8]
  [0.0 0.4 0.7 0.1 0.3 0.1 0.5]
  [0.6 0.0 0.4 0.7 0.5 0.1 0.5]
  [0.7 0.2 0.1 0.1 0.3 0.2 0.5]
  [0.6 0.5 0.2 0.5 0.5 1.0 0.6]
  [0.9 0.2 0.5 0.6 0.5 0.0 0.2]
  [0.9 0.9 0.2 0.6 0.2 0.1 0.2]
 ]
 [
  [0.8 0.3 0.9 0.5 0.5 0.3 0.2]
  [0.2 0.5 0.5 0.3 0.8 0.0 0.3]
  [0.3 1.0 0.3 0.8 0.3 0.8 0.8]
  [0.7 0.9 0.7 0.1 0.6 0.9 0.7]
  [0.4 0.3 0.8 0.7 0.5 0.8 0.3]
  [0.8 0.9 0.5 0.2 0.1 0.4 0.2]
  [0.4 0.7 0.5 0.2 0.7 0.1 0.3]
 ]
]
and it was not very different from: 
[
 [
  [0.5 0.2 1.0 0.4 0.9 0.2 0.4]
  [0.7 0.2 0.1 0.6 0.6 0.2 0.4]
  [0.8 0.3 0.6 0.7 0.4 0.3 0.9]
  [0.7 0.1 0.5 0.3 0.5 0.7 0.2]
  [0.5 0.6 0.7 1.0 0.4 0.1 0.5]
  [0.4 0.8 1.0 0.6 0.4 0.3 0.7]
  [0.8 1.0 0.7 0.6 0.3 0.7 0.8]
 ]
 [
  [0.4 0.6 0.1 0.2 0.1 0.2 0.7]
  [0.7 0.9 0.1 0.2 0.7 0.7 0.2]
  [0.9 0.6 0.0 1.0 0.6 0.7 0.8]
  [0.3 1.0 0.3 0.4 0.5 0.3 0.3]
  [0.8 0.7 0.3 0.1 0.3 0.7 0.5]
  [0.2 0.4 0.5 0.2 0.3 0.3 0.9]
  [0.9 0.7 0.4 0.1 0.2 0.9 0.8]
 ]
 [
  [0.1 0.0 0.7 0.3 0.8 0.2 0.1]
  [0.4 0.4 0.4 0.3 0.8 0.7 0.1]
  [0.3 0.3 0.0 0.0 0.1 0.2 1.0]
  [0.8 0.1 0.7 0.7 0.4 0.3 0.3]
  [0.7 0.1 0.9 0.6 0.4 0.9 0.3]
  [0.1 0.2 0.4 0.4 0.5 0.6 0.3]
  [0.6 0.5 0.5 0.9 0.7 0.5 0.6]
 ]
]