CODEWITHSUNDEEP
c#.netalgorithmrandom
anon
anon

Reputation:

How to implement a random number generator that is not random?

I need a random number generator that generates various number between n and m, but no with a equal probability. I want to set a value x between n and m where the possibility is the highest:

enter image description here

Is there an easy way to do that using the Random class? The likelihood should have the form of a binominal distribution or something similar (it is not important that its an exact binominal distributon, rough approximations are also ok)

EDIT

Maybe I have to clarify: I'm not looking for a binominal or gaussian distribution but also for something like this: enter image description here

I want to to define the value x where the highest likelihood should be.

EDIT

Unfortunately the previously accepted answer does not seem to work how i suspected. So I'm still looking for an answer!

Upvotes: 6

Views: 2385

Answers (4)

Dewfy
Dewfy

Reputation: 23624

Java SDK has good implementation Random.nextGaussian (taken from http://download.oracle.com/javase/1.4.2/docs/api/java/util/Random.html#nextGaussian())

I hope it is rather clear how to parse from java source to c#

synchronized public double nextGaussian() {
    if (haveNextNextGaussian) {
            haveNextNextGaussian = false;
            return nextNextGaussian;
    } else {
            double v1, v2, s;
            do { 
                    v1 = 2 * nextDouble() - 1;   // between -1.0 and 1.0
                    v2 = 2 * nextDouble() - 1;   // between -1.0 and 1.0
                    s = v1 * v1 + v2 * v2;
            } while (s >= 1 || s == 0);
            double multiplier = Math.sqrt(-2 * Math.log(s)/s);
            nextNextGaussian = v2 * multiplier;
            haveNextNextGaussian = true;
            return v1 * multiplier;
    }
 }

UPDATE: How I've made shift of median:

public static float gaussianInRange(float from, float mean, float to)
{
    if( !(from < mean && mean < to) )
        throw new IllegalArgumentException(MessageFormat.format("RandomRange.gaussianInRange({0}, {1}, {2})", from, mean, to));

    int p = _staticRndGen.nextInt(100);
    float retval;
    if (p < (mean*Math.abs(from - to)))
    {
        double interval1 = (_staticRndGen.nextGaussian() * (mean - from));
        retval = from + (float) (interval1);
    }
    else
    {
        double interval2 = (_staticRndGen.nextGaussian() * (to - mean));
        retval = mean + (float) (interval2);
    }
    while (retval < from || retval > to)
    {
        if (retval < from)
            retval = (from - retval) + from;
        if (retval > to)
            retval = to - (retval - to);
    }
    return retval;
}

Upvotes: 5

bestsss
bestsss

Reputation: 12056

smth relatively simple. You can generate 2 random numbers: 1st defines how close to x the 2nd random number would be.

You can use any breakpoint/function levels you like.

Upvotes: 0

Felice Pollano
Felice Pollano

Reputation: 33252

You need a generator working on a "Normal Distribution". Have a look here: http://www.csharpcity.com/reusable-code/random-number-generators/

Upvotes: 1

Mark Byers
Mark Byers

Reputation: 838156

You can use the Box-Muller transform to generate a sequence of psuedorandom normally distributed numbers from a sequence of numbers uniformally distributed between 0 and 1.

Box-Muller transform

Upvotes: 6

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