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 use strict;
 use warnings;

- my @matrix = ( $n , $n );
+ my @matrix;

@array = (
  1,      2,       3,       <-- $i = 0
...
  |       |        |
  $j = 0  $j = 1   $j = 2
);

@array = (
  [ 1,      2,       3       ],  # <-- $i = 0
...
    |       |        |
    $j = 0  $j = 1   $j = 2
);

@array = ([ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]);
          ^^^^^^^^^^^  ^^^^^^^^^^^  ^^^^^^^^^^^
...
# <nested_array1> = 1, 2, 3
# <nested_array2> = 4, 5, 6
# <nested_array3> = 7, 8, 9

@array = ( 5, 5 );

@array = ();

# $i = 0, $j = 0, $k = 1
@array = ( [ 1 ] );

@array = ( [ 1, 2 ] );

@array = ( [ 1, 2, 3 ] );

@array = ( [ 1, 2, 3 ], [ 4 ] );