my $two_d = [
   [1,2,3],
   [4,5,6],
   [7,8,9],
];

# how many columns?
print scalar @$two_d;

# how many rows in second column?
print scalar @{ $two_d->[1] };

##</code><code>##

use Math::Matrix;
use Data::Dumper;

my $two_d = [
   [1,2,3],
   [4,5,6],
   [7,8,9],
];

my $m = Math::Matrix->new($two_d);
print Dumper $m;