Advanced Perl Programming

that is reference counted, not the name.)

Example 2.1: Reading a Matrix from a File

sub matrix_read_file { my ($filename) = @_;

open (F, $filename) || die "Could not open $filename: $!"; while ($line = <F>) { chomp($line);

next if $line =~ /^\s*$/; # skip blank lines if ($line =~ /^([A-Za-z]\w*)/) {

$matrix_name = $1; } else {

my (@row) = split (/\s+/, $line);

push (@{$matrix_name}, \@row;) # insert the row-array into

# the outer matrix array } }

close(F); }

Now let us use this array-of-arrays structure to multiply two matrices. In case you have forgotten how matrix multiplication works, the product of two matrices A_mn (m rows, n columns) and B_np is defined as

^j ⁼ 2 Aft . ^Ekj

The element (i, j) of the matrix product is the sum of successive pairs of elements taken from the i _th row of A and the j_th column of B. Translated into Perl, it looks like Example 2.2.

Example 2.2: Matrix Multiply

sub matrix_multiply {

my ($r_mat1, $r_mat2) = @_; # Taking matrices by reference

my ($r_product); # Returing product by reference

my ($r1, $c1) = matrix_count_rows_cols ($r_mat1);

my ($r2, $c2) = matrix_count_rows_cols ($r_mat2);

die "Matrix 1 has $c1 columns and matrix 2 has $r2 rows."

. " Cannot multiply\n" unless ($c1 == $r2); for ($i = 0; $i < $r1; $i++) {

for ($j = 0; $j < $c2; $j++) { $sum = 0; for ($k = 0; $k < $c1; $k++) {

$sum += $r_mat1->[$i][$k] * $r_mat2->[$k][$j]; }

$r_product->[$i][$j] = $sum; }