You could save another few lines like this 
#prepopulate copy error array;
sub popfilea {
  foreach my $ya ( 0 .. $gener ) {
    foreach my $xa ( 0 .. $total ) {
      $aoa[$xa][$ya] = (int rand(1+2*$copyerr)-$copyerr ) /$PCNT;
    }
  }
}

[download]
and here 
sub popnum1 {
  ( $x, $y ) = @_;
  if ( ($y==0) || ($aod[$x][ $y-1 ] ne 'a') ) {
     return $initial + $aoa[$x][0];
  } else {
     return $aoa[$x][$y] + $aob[$x][ $y-1 ];
  }
}

[download]
moving the sprintf's to this line 
 
$coper = sprintf '%.2f', popnum1( $x, $y )

[download]
or consider combining the two subs into one so that you have 
 
$coper = sprintf '%.2f', popnum( $model, $x, $y )

[download]
hth poj

In reply to Re^2: This runs WAY too slow by poj
in thread This runs WAY too slow by Dandello

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