(x,y)

-1,1      |     1,1
----------+----------  <-- origin (0,0)
-1,-1     |     1,-1

##</code><code>##

use strict;
my (@pp_grid, @pn_grid, @nn_grid, @np_grid, @input);

#INPUT
push @pp_grid, [ @input ] for @input;
push @pn_grid, [ @input ] for @input;
push @nn_grid, [ @input ] for @input;
push @np_grid, [ @input ] for @input;

@pp_grid = (
[ qw( a b c d ) ],
[ qw( e f g h ) ],
[ qw( i j k l ) ],
[ qw( m n o p ) ],
);

@pn_grid = (
[ qw( q r s t ) ],
[ qw( u v w x ) ],
[ qw( y z 1 2 ) ],
[ qw( 3 4 5 6 ) ],
);

@nn_grid = (
[ qw( A B C D ) ],
[ qw( E F G H ) ],
[ qw( I J K L ) ],
[ qw( M N O P ) ],
);

@np_grid = (
[ qw( Q S T U ) ],
[ qw( V W X Y ) ],
[ qw( Z 7 8 9 ) ],
[ qw( 0 ? ! & ) ],
);

#OUTPUT
print "pp_grid:\n";
print "@$_\n" for @pp_grid;
print "\n";
print "np_grid:\n";
print "@$_\n" for @np_grid;
print "\n";
print "nn_grid:\n";
print "@$_\n" for @nn_grid;
print "\n";
print "pn_grid:\n";
print "@$_\n" for @pn_grid;

print " and here is 1,-1: $pn_grid[1][1]\n";
print " and here is 1,1: $pp_grid[1][1]\n";
print " and here is -1,1: $np_grid[1][1]\n";
print " and here is -1,-1: $nn_grid[1][1]\n";