Question

I am trying to write a script for matrix multiplication. Its just a basic program but I am not able to figure it out about the following error :

Global symbol “@ref_mat1” requires explicit package name at multiplication.pl line 49.

Global symbol “@ref_mat2” requires explicit package name at multiplication.pl line 49.

Below is my script :

 #!/usr/bin/perl -w
    use strict;

     my @mat1=(
        [2,3,4],
        [1,2,3],
        [3,4,5]
            );

    my @mat2=(
            [2],
            [3],
            [4]
           );


    my ($i, $j, $k);
    my $r_product=[];

   $r_product= mat_multiplication(\@mat1,\@mat2);

    sub mat_multiplication
        {

         my ($ref_mat1,$ref_mat2)=@_;
         my($mat1_row,$mat1_col)=total_rows_column($ref_mat1);
         my($mat2_row,$mat2_col)=total_rows_column($ref_mat2);
             for($i=0;$i<$mat1_row;$i++)
            {
               for($j=0;$j<$mat2_col;$j++)
                {
                   my $sum=0;
                   for($k=0;$k<$mat1_col;$k++)
                    {
                      $sum=$sum+$ref_mat1[$i][$k]*$ref_mat2[$k][$j];
                    }
                    $r_product->[$1][$j]=$sum;
                }
            } 
            return $r_product;

        }


    sub total_rows_column
             { 
              my($r_mat) =@_;
              my $num_row=@{$r_mat};
              my $num_col=@{$r_mat->[0]};
              return($num_row,$num_col);
             }

I searched for this problem and found one link

Explanation of 'global symbol requires explicit package name'

But still not able to resolve it. Please just have a look an let me know where am i doing mistake.

Thanks

Answer 1

$ref_mat1 and $ref_mat2 are references to arrays. In Perl if you want to access a reference to an array you cannot use $reference[$idx] directly — you have to use the -> operator after the reference like this: $ref_mat1->[0].

Without it Perl thinks that $ref_mat1[0] refers to an array @ref_mat1 which doesn’t exist. Yes, both $var and @var can exist at the same time with differing content, see this example:

use strict;
use Data::Dumper;

my $abc = 42;
my @abc = (1, 2, 3);

print Dumper($abc), Dumper(\@abc);