Re: Generating Random Numbers with Normal Distribution

On Dec 10, 2007 2:28 PM, AmirBehzad Eslami <behzad.eslami@gmail.com> wrote: > Dear list, > > For some computer-based simulation, i need to > generate random numbers that have a normal distribution. > > It seems that PHP's rand() and mt_rand() functions return > uniformly distributed numbers which is not suitable for > simulation purposes. > > Is there any way to generate random numbers with > normal distribution in PHP? > this is straight from a comment on the rand() documentation: http://us3.php.net/rand -nathan Random numbers with Gauss distribution (normal distribution). A correct alghoritm. Without aproximations, like Smaaps' It is specially usefull for simulations in physics. Check yourself, and have a fun. <?php function gauss() { // N(0,1) // returns random number with normal distribution: // mean=0 // std dev=1 // auxilary vars $x=random_0_1(); $y=random_0_1(); // two independent variables with normal distribution N(0,1) $u=sqrt(-2*log($x))*cos(2*pi()*$y); $v=sqrt(-2*log($x))*sin(2*pi()*$y); // i will return only one, couse only one needed return $u; } function gauss_ms($m=0.0,$s=1.0) { // N(m,s) // returns random number with normal distribution: // mean=m // std dev=s return gauss()*$s+$m; } function random_0_1() { // auxiliary function // returns random number with flat distribution from 0 to 1 return (float)rand()/(float)getrandmax(); } ?> JanS student of astronomy on Warsaw University