LeastSquaresMethod

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
my $data = [];
while (<>) {
  chomp;
  my ($x, $dummy1, $y, $dummy2) = split;
  push @$data, [$x, $y];
}
my $a;
my $b;
while (1) {
  my $sum_xy = 0.;
  my $sum_x = 0.;
  my $sum_y = 0.;
  my $sum_x2 = 0.;
  foreach my $d (@$data) {
    my ($x, $y) = @$d;
    $sum_xy += $x * $y;
    $sum_x += $x;
    $sum_y += $y;
    $sum_x2 += $x ** 2;
  }
  my $n = @$data;
  $a = ($n * $sum_xy - $sum_x * $sum_y) / ($n * $sum_x2 - $sum_x ** 2);
  $b = ($sum_x2 * $sum_y - $sum_xy * $sum_x) / ($n * $sum_x2 - $sum_x ** 2);
  my $ys = 0.;
  foreach my $d (@$data) {
    my ($x, $y) = @$d;
    $ys += ($y - $a * $x - $b) ** 2;
  }
  my $error = 3 * sqrt($ys / ($n - 1));
  my $i = 0;
  foreach my $d (@$data) {
    my ($x, $y) = @$d;
    splice @$data, $i, 1 if abs($y - $a * $x - $b) >= $error;
    $i++;
  }
  last if $n == @$data;
}
say "y = ${a} * x + ${b}";