Different probability for ranges of random numbers

Question

I\'m looking for the best way of implementing random number generator, that will allow me to have control over probability from what range the generated number will be retur

Answer 1

It sounds to me like what you're looking for is a way to generate numbers on a normal (or Gaussian) distribution (take a look at the Wikipedia page if you don't know what that means).

The Box-Muller transformation can be used to generate pairs of normally distributed numbers.

Here is a c++ implementation of the polar form of the Box-Muller transformation that shouldn't be hard to translate to javascript.

// Return a real number from a normal (Gaussian) distribution with given
// mean and standard deviation by polar form of Box-Muller transformation
double x, y, r;
do
{
    x = 2.0 * rand() - 1.0;
    y = 2.0 * rand() - 1.0;
    r = x * x + y * y;
}
while ( r >= 1.0 || r == 0.0 );
double s = sqrt( -2.0 * log(r) / r );
return mean + x * s * stddev;

Where mean is the mean of the normal distribution and stddev is the Standard Deviation of the distribution. This code is from a MersesenneTwister C++ class that I've been using recently that you can find on Rick Wagner's page. You can find some more useful information about the Box-Muller transformation on this page.