True. And thanks for pointing that out, enlightening. However, I still feel like

my $matrix =[ [1,5,7],
                [2,3,4],
                [5,1,9],
                [7,8],
                [3]
              ] ;
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feels more "aesthetically" right than setting it up with @matrix like you did above, and then $matrix = \@matrix... even if both are equivalent.