Avoid adding and subtracting numbers that vary greatly in magnitude. For example, 

sub bad_average {
   my $acc = 0;
   $acc += $_ for @_;
   return $acc / @_;
}

sub better_average {
   my $acc = 0;
   $acc += $_/@_ for @_;
   return $acc;
}

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When you do comparisons, use a tolerance. For example, 

bad:     if ($x == $y)
abs tol: if (abs($x - $y) < $abs_tol)
rel tol: if (abs($x - $y) < abs($x) * $rel_tol)

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Avoid accumulation of error. For example, 

bad:  for (my $x=0; $x<100; $x+=0.1) { ... }
good: for (0..99) { my $x = $_/10; ... }

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Deal with the integers when possible instead of floats. For example, work with cents instead of dollars.

In reply to Re: Floating Point Errors by ikegami
in thread Floating Point Errors by Anonymous Monk

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