[PD-dev] Pd's RNG.....

[chun lee]

Thanks for your reply, I will look into that and make sense out of it, I
hope:) unfortunately, I am having a fever with splitting headache at the
moment, so it might take me a while.

Apologies for opened up 2 thread on Pd's RNG questions..

On 25/10/04 2:44 pm, "Matju" <matju at sympatico.ca> wrote:

> 
> On Mon, 25 Oct 2004, chun lee wrote:
>> On 24/10/04 12:59 pm, "Tim Blechmann" <TimBlechmann at gmx.net> wrote:
>>>> Just wondering, does the methods used in Pd's [noise~] and [random]
>>>> the implementation of minimal standard/Lehmer RNG method? Or something
>>>> similar?
>>> see doc/5.reference/help-random.pd ... random and noise are using the
>>> same algorithm ...
>> Thanks, I forgot to check the help files, my bad;(
>> In addition,  I found the below info on RNG while I was search on net.
>> http://www.sbc.su.se/~per/crng/seminar/rng5.html
>> http://www.cs.virginia.edu/~jcc5t/classes/undergrad/simulation/random/rng.c
> 
> Some more info on the linear congruential method: the m can be anything
> (in Pd it's 1<<32 exactly, because it's faster). To have the longest
> possible period, where all numbers in the range are visited, i think the
> conditions are that a,b,m are all coprime. Since m is a power of two this
> just forces a,b to be odd, which they would have been anyway, and then the
> only condition left is that a,b are coprime, that is, gcd(a,b)=1. However
> you want to make it look random so you have to make a and b big enough
> values that looks like nothing you already know. (else, you see, a=0 b=1
> would be a good candidate ;-)
> 
> Then it only looks vaguely random. Obviously, if it guarantees to visit
> all 1<<32 numbers before duplicates come, it's not very random. I once
> filled a 256*256 grid (or something) using QuickBASIC (that was long ago)
> and that algorithm, and I could see patterns in the filling process.
> What's important to make it look random is to carefully avoid putting it
> in a situation where the nonrandomness is exhibited (duh). In the case of
> [noise~] no-one has an ear fine enough to find that it's
> linear-congruential.
> 
> _____________________________________________________________________
> Mathieu Bouchard -=- Montréal QC Canada -=- http://artengine.ca/matju
> 
>