🚀 go-pugleaf

>>>>> On Mon, 7 Sep 1992 00:53:03 GMT, waugh@probitas.cs.utas.edu.au (Sam Waugh) said:

> I was wondering if anybody has implemented a random number generator
> in Haskell?  I am trying to use Haskell for some neural network
> applications and definitely need a good random function.  Otherwise

Here is one I wrote in Miranda (you didn't say if you wanted uniform
or normal variates, so I give you both.)

Tim

>|| random.m

random is given a positive integer seed and returns an infinite list
of uniform random numbers between 0 and 1.  We use a linear
congruential generator (see "Art of Computer Programming Vol 2")

> random :: num -> [num]
> random = map (/modulus) . iterate f
>          where f x = (x*multiplier) mod modulus
> multiplier = 69069
> modulus = 2^32

normal_random is given a seed and returns an infinite list of random
normal variates with mean 0 and variance 1.  (Box Muller method see
"Art of Computer Programming Vol 2")

> normal_random :: num -> [num]
> normal_random = box_muller.(map f).random
>		  where f x = 2*x - 1

box_muller takes a stream of uniform random numbers on [-1,1] and
returns a stream of normally distributed random numbers.

> box_muller :: [num] -> [num]
> box_muller (x1:x2:xs) = x1*m:x2*m:rest, if r <= 1
>		        = rest, otherwise
>			  where r = x1^2 + x2^2
>			        m = sqrt(-2*log r/r)
>			        rest = box_muller xs