Question

I want to compute covariance using PDL, but the problem is that it always shows an error:

Undefined subroutine &main::cov called at line 12.

Can anyone tell me where I’m making a mistake?

#! usr/bin/perl

use strict;
use warnings;
use PDL;

my $a = random(5, 3);
my $b = random(5, 3);

print "$a\n$b\n";

my $cov = cov($a, $b);     #line 12

print "$cov\n";

Answer 1

That error message tells you that a function named cov is not exported by default by PDL. If I search the PDL CPAN page (using the grep tool), I do not see a function named cov.

A google search yields PDL::Stats::Basic, which has a cov function.