how can i generate random numbers with predefined mean and standard deviation

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Re: how can i generate random numbers with predefined mean and standard deviation by Zaxo (Archbishop) on Aug 23, 2003 at 17:53 UTC
Math::Random has exactly what you need, `use Math::Random; my @randoms = random_normal 1000, 250, 20;` [download] Being random, that does not guarantee the the sample you get will have exactly that mean and sd, just close. If you need a distrubution other than normal, Math::Random has many to choose from. After Compline, Zaxo	[reply] [d/l]
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Re: how can i generate random numbers with predefined mean and standard deviation by simonm (Vicar) on Aug 23, 2003 at 18:15 UTC
Laziness is a virtue. Before writing code, check to see if someone else has already solved this problem. Searching CPAN for "random AND deviation"... Result #1 is Math::Random. `use Math::Random 'random_normal'; my @random = random_normal(1000, 250, 20)` [download]	[reply] [d/l]
Re: how can i generate random numbers with predefined mean and standard deviation by Limbic~Region (Chancellor) on Aug 23, 2003 at 20:59 UTC
babloo, Ok - not knowing the reason you are supposed to do this without a module I didn't spend a lot of time trying to come up with a scientific solution. I did find that the following code did work surprisingly well for the requirements you specified: #!/usr/bin/perl -w use strict; my $desired_mean = 250; my $desired_deviation = 20; my $total = 1000; my @numbers; gen_numbers(\@numbers, $desired_mean, $desired_deviation, $total); sub gen_numbers { my ($array_ref, $mean, $deviation, $total) = @_; my $offset = $deviation * 1.75; my $low = $mean - $offset; my $high = $mean + $offset; for (0 .. $total) { my $number; while (1) { $number = int(rand($high)) + 1; last if ($number >= $low && $number <= $high); } push @{$array_ref} , $number } } my $sum; $sum += $_ for @numbers; my $mean = $sum / $total; my $scratch; for (@numbers) { $scratch += (($_ - $mean) * ($_ - $mean)); } my $standard_deviation = sqrt($scratch / ($total - 1)); print "Desired Mean: $desired_mean\n"; print "Mean: $mean\n"; print "\n"; print "Desired Standard Deviation: $desired_deviation\n"; print "Standard Deviation: $standard_deviation\n"; __END__ Desired Mean: 250 Mean: 250.06707 Desired Standard Deviation: 20 Standard Deviation: 19.9571308028178 [download] I doubt seriously it will work for anything other than 20 for a standard deviation since I used the fact that 3 standard deviations from the mean accounts for 99.7% in a normal distribution. I then fudge factored the remaining .3%. Cheers - L~R	[reply] [d/l]
Re: how can i generate random numbers with predefined mean and standard deviation by davido (Cardinal) on Aug 23, 2003 at 18:08 UTC
There's a pretty good discussion on a close variation of that question here: 26889 Dave "If I had my life to do over again, I'd be a plumber." -- Albert Einstein	[reply]
Re: how can i generate random numbers with predefined mean and standard deviation by zentara (Cardinal) on Aug 24, 2003 at 19:33 UTC
gjb wrote about the "Numerical recipes in C" book at book They make you download about 60 small pdfs to get the whole book. I made a simple wget script to get the whole book if you are interested. numerical-c-grabber It's just a brute force script, it was just too easy to cut'n'paste a lynx dump and put in a bunch of wget's. :-)	[reply]