View difference between Paste ID: ygvEUW3k and XKyfR39V

 #!/usr/bin/perl
 use strict;
 use warnings;
 use feature 'say';
 my $data = [];
 while (<>) {
   chomp;
-  my ($x, $dummy1, $y, $dummy2) = split;
+  my ($x, $xe, $y, $ye) = split;
-  push @$data, [$x, $y];
+  push @$data, [$x, $xe, $y];
 }
-my $a;
+my ($a, $b, $a_err, $b_err);
-my $b;
+
   my ($sum_w, $sum_xy, $sum_x, $sum_y, $sum_x2) = (0., 0., 0., 0, 0.);
-  my $sum_xy = 0.;
+
-  my $sum_x = 0.;
+    my ($x, $xe, $y) = @$d;
-  my $sum_y = 0.;
+    my $w = ($xe == 0.) ? 1 : 1 / $xe;
-  my $sum_x2 = 0.;
+    $sum_w += $w;
     $sum_xy += $w * $x * $y;
-    my ($x, $y) = @$d;
+    $sum_x += $w * $x;
-    $sum_xy += $x * $y;
+    $sum_y += $w * $y;
-    $sum_x += $x;
+    $sum_x2 += $w * $x ** 2;
-    $sum_y += $y;
+
-    $sum_x2 += $x ** 2;
+
   my $denom = $sum_w * $sum_x2 - $sum_x ** 2;
   $a = ($n * $sum_xy - $sum_x * $sum_y) / $denom;
-  $a = ($n * $sum_xy - $sum_x * $sum_y) / ($n * $sum_x2 - $sum_x ** 2);
+  $b = ($sum_x2 * $sum_y - $sum_xy * $sum_x) / $denom;
-  $b = ($sum_x2 * $sum_y - $sum_xy * $sum_x) / ($n * $sum_x2 - $sum_x ** 2);
+  $a_err = $sum_x2 / $denom;
-  my $ys = 0.;
+  $b_err = $sum_w / $denom;
   my $diff = 0.;
-    my ($x, $y) = @$d;
+
-    $ys += ($y - $a * $x - $b) ** 2;
+    my ($x,, $y) = @$d;
     $diff += ($y - $a * $x - $b) ** 2;
-  my $error = 3 * sqrt($ys / ($n - 1));
+
   my $error = 3 * sqrt($diff / ($n - 1));
   my $i = 0;
-    my ($x, $y) = @$d;
+
     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}";
+
 say "y = ${a} * x + ${b}";
 say "a_err: ${a_err}, b_err: ${b_err}";