Thanks for your response. Below is a sub to estimate the Pearson correlation coefficient estimation.

sub correlate($$) {
# $_[0] = ref to x array
# $_[1] = ref to y array

    my $x = $_[0];
    my $y = $_[1];

    if (scalar(@$x) != scalar(@$y)) {
        return;
        }

    my $s_xy = 0;
    my $s_xx = 0;
    my $s_yy = 0;
    my $s_x  = 0;
    my $s_y  = 0;
    my $n    = scalar(@$x);

    foreach (my $i = 0; $i < scalar(@$x); $i++) {
        $s_xx += $$x[$i] * $$x[$i];
        $s_xy += $$x[$i] * $$y[$i];
        $s_yy += $$y[$i] * $$y[$i];
        $s_x  += $$x[$i];
        $s_y  += $$y[$i];
        }

    my $S_xy = ($n * $s_xy) - ($s_x * $s_y);
    my $S_xx = ($n * $s_xx) - ($s_x * $s_x);
    my $S_yy = ($n * $s_yy) - ($s_y * $s_y);
    my $denm = ($S_xx**0.5) * ($S_yy**0.5);

    my $p = $S_xy / $denm;

    return $p;

    }
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