# Re: Randomness as a computational resource

**From:** none (*_at_(none)*)

**Date:** 07/03/05

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Date: Mon, 04 Jul 2005 08:06:43 +1200

Douglas A. Gwyn wrote:

*> A source of "randomness" (entropy) *is* useful at times,
*

*> for example in stochastic simulations or generating crypto
*

*> keys. (The former application can usually get by with a
*

*> "pseudo"random source, i.e. a completely deterministic one.)
*

In fact we prefer a pseudo random number generator. Why? Well one reason

is if--heaven forbid, there is a bug that comes up in a test. If you use

real random numbers duplication the bug is rather difficult... With a

pseudo rng its trivial.

But some simulations are sensitive to the lack of randomness esp in LCC

generators. I usually test with a non-linear rng as well to show that it

makes no difference. In fact lately i use the full 2^48 length of the

Java LCC, and have needed to use the non-linear one anyways. I use AES

in counter mode. Its only five times slower than a LCC, which is fast

for non-linear. Some use the BBS generator, but i find it far to slow.

Some stochastic Algo's use the unrandomness of pseudo RNG to improve

there convergent properties. In particular stochastic integration can

improve on the base performance by using a LFSR m-sequence to speed it

up quite a bit (numerical recipes in C has some details).

greg

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