use Data::Dumper;
say Dumper \@rot_mat;

##</code><code>##

$rot_mat[0][0]=cos($phi_rad)*cos($theta_rad)*cos($psi_rad)-sin($phi_rad)*sin($psi_
+rad);

##</code><code>##

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
use feature qw/ say /;

my @a;
$a[0][0] = 'foo';
$a[0][1] = 'bar';
$a[1][0] = 'baz';
$a[1][1] = 'quux';

say Dumper @a;

say $a[0];

for ( @a ) {
   say (join ' ', @{ $_ });
}

##</code><code>##

[05:58][nick:~/monks]$ perl 1134141.pl
$VAR1 = [
          'foo',
          'bar'
        ];
$VAR2 = [
          'baz',
          'quux'
        ];

ARRAY(0x7feb6b006280)

foo bar
baz quux