use Data::Dumper;

my @multi;
foreach my $i ( 10 .. 12 ) {
    foreach my $j ( 10 .. 12 ) {
        $multi[$i-10][$j-10] = "$i,$j";
    }
}
my $what_is_this = $multi[1];
print Dumper $what_is_this;
__END__
$VAR1 = [
          '11,10',
          '11,11',
          '11,12'
        ];

##</code><code>##

my $n = scalar @{ $multi[1] };