pdl [
      [4, 2, 6, 8],
      [2, 5, 3, 4],
      [9, 5, 5, 6],
      [7, 4, 3, 6],
    ],

pdl [
      [21, 11.5, 15.5, 22],
      [2, 5, 3, 4],
      [9, 5, 5, 6],
      [7, 4, 3, 6],
    ],

##</code><code>##

my @rows;
my $j = 0;
{
  local @ARGV = $ARGV[ 0 ];
  while ( <> ) {
    my $i = 0;
    $rows[ $i++ ][ $j ] = $_ for split;
    $j++;
  }
}

my $dmat  = pdl [ @rows[ 0, 1, 2, 3 ] ];
my $damat = pdl [ @rows[ 4, 1, 2, 3 ] ]; 
my $dbmat = pdl [ @rows[ 0, 4, 2, 3 ] ];
my $dcmat = pdl [ @rows[ 0, 1, 4, 3 ] ];
my $ddmat = pdl [ @rows[ 0, 1, 3, 4 ] ];

# proceed to compute the determinants of the $dmat, $damat, etc.