Simple decay simulation

decay.pl

#!/usr/bin/perl

use strict;
use warnings;
use 5.010;

my @PNS = ( 3, 4, 5, 6 );
my $lambda = 0.1;

for my $PN ( @PNS ){
    my $N0 = 10**$PN;
    my $N = $N0;
    my @nDecay;
    my @nRemain;
    my @ratio;
    while( $N >= $N0/2 ){
        my $dn = 0;
        push @nRemain, $N;
        for( my $i=0;$i< $N; $i++ ){
            $dn++ if( rand(1) < $lambda );
        }
        push @nDecay, $dn;
        push @ratio, $dn/$N;
        $N -= $dn;
    }
    print "$N0\t";
    map { printf "%7d/%7d/%.3f\t", $nRemain[$_], $nDecay[$_], $ratio[$_];} 0..$#nDecay;
    my $avg_ratio = 0;
    $avg_ratio += $_ for @ratio;
    $avg_ratio /= @ratio;
    printf "( %d , %.3f )\n", scalar(@nDecay), $avg_ratio;
}

result.txt

1000	   1000/     92/0.092	    908/     94/0.104	    814/     85/0.104	    729/     74/0.102	    655/     77/0.118	    578/     59/0.102	    519/     47/0.091	( 7 , 0.102 , 0.008)
10000	  10000/    953/0.095	   9047/    906/0.100	   8141/    820/0.101	   7321/    777/0.106	   6544/    664/0.101	   5880/    614/0.104	   5266/    533/0.101	( 7 , 0.101 , 0.003)
100000	 100000/   9998/0.100	  90002/   8998/0.100	  81004/   8197/0.101	  72807/   7193/0.099	  65614/   6518/0.099	  59096/   5895/0.100	  53201/   5309/0.100	( 7 , 0.100 , 0.001)
1000000	1000000/  99788/0.100	 900212/  89583/0.100	 810629/  81166/0.100	 729463/  73524/0.101	 655939/  65736/0.100	 590203/  59183/0.100	 531020/  52851/0.100	( 7 , 0.100 , 0.000)