Random numbers in the shape of a bell curve

Question

I need to manipulate random to produce a statistical average with the shape of a bell curve, here is my attempt:

Function slopedrand(max As Single, bias As Single) As Integer
    Dim count As Single = 0
    While count < bias
        max = rand.NextDouble() * max
        count += rand.NextDouble()
    End While
    Return rand.NextDouble() * max
End Function

Function bulgedrand(min As Single, max As Single, bulge As Single, bias As Single)
    Dim negative = bulge - min
    Dim positive = max - bulge

    Dim nr = min + slopedrand(negative, bias)
    Dim pr = max - slopedrand(positive, bias)

    Return rand.NextDouble() * (pr - nr) + nr
End Function

however, given that I suck at math, all it produces is stuff like this: https://i.stack.imgur.com/4YTba.png

which is more like a bulge...

Since it feels like my skull is boiling, maybe somebody here has figured out how to accomplish what I need and will spare me from further attempts of thinking?

(the example is given in vb.net since it was quick to prototype on but any language is welcome)

What language is this regarding? It looks like vb.net at a guess. — Robadob, Aug 07 '15 at 09:17
Won't `rand() + rand()` basically give you something approaching a Bell curve? — paxdiablo, Aug 07 '15 at 09:17
When you say "Bell curve", do you mean a normal (Gaussian) distribution? If so then I can make my answer more specific. — Bathsheba, Aug 07 '15 at 09:21
I'm pretty sure it's vb.net, vb6 and vba do not allow you to declare and define in the same "statement". But the OP could confirm... — Bathsheba, Aug 07 '15 at 09:23
Please do not delete questions just because you think you have understood them (and “I switched to `double`” is barely an explanation). Talking about your recently deleted question, obviously. — Pascal Cuoq, Aug 08 '15 at 22:36

score 2 · Accepted Answer · answered Aug 07 '15 at 09:19

The "established" way of doing this is to draw a uniformly distributed random number in the range [0, 1), then apply the quantile function of the Bell curve distribution. This then gives you a random number that has the same distribution as the Bell curve.

score 0 · Answer 2 · edited May 23 '17 at 12:33

0

A bell curve can be approximated by a normal distribution, so I guess you can use random values inside the formula for a normal distribution and get the effect you need, such as in this answer:

drawing random number from a standard normal distribution using the standard rand() functions

Maybe it can help you?

edited May 23 '17 at 12:33

Community

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answered Aug 07 '15 at 09:19

Bruno Oliveira

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Random numbers in the shape of a bell curve

2 Answers2