matrix multiplication

benben has asked for the wisdom of the Perl Monks concerning the following question:

Hi y'all, I am trying to read 2 matrices from files, multiply them and print. However, I keep getting error: "can't use string ("1") as an ARRAY ref at line 45" ...can't figure out what the problem is. My code:

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

my $first = $ARGV[0];
my $second = $ARGV[1];
unless (defined($ARGV[0])) {
    print "Insert filename of the first matrix: ";
    chomp($first = <STDIN>);
}
unless (defined($ARGV[1])) {
    print "Insert filename of the second matrix: ";
    chomp($second = <STDIN>);
}

my @AoA;
my $cols = 0;
my $rows = 0;
my @mat1 = readmatrix ($first);
my ($r1, $c1) = ($rows, $cols);
$cols = 0;
$rows = 0;
my @mat2 = readmatrix ($second);
my ($r2, $c2) = ($rows, $cols);

my @product = multiply(\@mat1, \@mat2);

printmatrix (@product);

sub readmatrix {
    my ($file) = @_;
    open(IN, "$file") || die "can't open file: $!\n";
    while (defined (my $line = <IN>)) {
        my @tmp = split(' ', $line);
        $cols = scalar @tmp;
        $rows++;
        push (@AoA, [@tmp]);
    }
    close IN;
}

sub multiply {
    my ($mat1,$mat2) = @_;
    die "unmatching matrices!\n" unless ($c1 eq $r2);
    my $product;
### HERE IS THE BUG SOMEWHERE... ###
    for (my $i=0; $i<$r1; $i++) {
        for (my $j=0; $j<$c2; $j++) {
                    for (my $k=0; $k<$c1; $k++) {
                $product->[$i][$j] += $mat1->[$i][$k] * $mat2->[$k][$j
+];
            }
        }
    }
    return $product;
}

sub printmatrix {
    my (@AoA) = @_;
    for (my $x = 0; $x <= $#AoA; $x++) {
        print join("\t", @{$AoA[$x]}), "\n";
    }
}
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Comment on matrix multiplication Download Code

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Re: matrix multiplication by trizen (Hermit) on Apr 21, 2012 at 18:58 UTC
1. Add `return @AoA;` at the end the `readmatrix` subroutine 2. Inside of the `multiply` sub, change `return $product;` into `return @{$product};` - or use an array in the first place.	[reply] [d/l] [select]
Re: matrix multiplication by JavaFan (Canon) on Apr 21, 2012 at 19:14 UTC
You are assigning the return value of `close` to to `@mat1` and `@mat2`. Really, before asking a question here, some basic debugging would be good. At least you could have tested whether `multiply` got the parameters you expected -- and then you could have realized that the bug is nowhere near you think it was.	[reply] [d/l] [select]
Re: matrix multiplication by Cristoforo (Curate) on Apr 21, 2012 at 20:47 UTC
Not exacly an answer to your question, but there is a module Math::Matrix that has a multiply function (for 2 matrices) see here.	[reply]
Re: matrix multiplication by jwkrahn (Abbot) on Apr 22, 2012 at 03:37 UTC
`my @mat1 = readmatrix ($first); my ($r1, $c1) = ($rows, $cols); ... sub readmatrix { my ($file) = @_; open(IN, "$file") \|\| die "can't open file: $!\n"; while (defined (my $line = <IN>)) { my @tmp = split(' ', $line); $cols = scalar @tmp; $rows++; push (@AoA, [@tmp]); } close IN; }` [download] That would probably be better as: `my ( $r1, $c1, @mat1 ) = readmatrix( $first ); ... sub readmatrix { my ( $file ) = @_; open my $IN, '<', $file or die "can't open file: $!\n"; my @AoA; while ( <$IN> ) { push @AoA, [ split ]; } return $., scalar @{ $AoA[ -1 ] }, @AoA; }` [download]	[reply] [d/l] [select]