"gregjohn" <pte### [at] yahoocom> wrote:
> The neatly ordered, predictable pattern of red dots in the top half of the image
> are generated with povray's rand() function.  They demonstrate what you get if
> you cause a monotonic increase in the seed value.  Once I had a project
> "ruined" by this predictable pattern because I was exploring some parameter
> space via use of the #declare RSEED=seed(frame_number).
>
> The green dots below represent my best attempt so far to create something worthy
> of the title "random function".   It requires one first to set an "aseed" value
> between 0 and 1, but this aseed *may* increase monotonically, like #declare
> aseed=(frame_number+0.1)/(final_frame+0.1);

This was the problem I found with my stochastic rig - esp because I was seeding
each frame's RNG with frame_number. I wrote some (non-mathematically-robust)
functions to increase the quality of the random numbers I was using for a few
key parameters. They helped for my code, but I don't really know if they were
increasing the randomness, or just hiding the problems from my uses. I've seen
papers about how to create high-quality random numbers from poor-quality RNGs,
but I'm not mathematically adept enough to understand them...

In the end I found myself using halton sequences more and more - they are
decidedly non-random, but what I was really using the RNG for was to create low
discrepancy samples, and the halton sequence seemed better than a RNG for that
purpose.

A (ever-so slightly buggy) version of both a RNG massager, and a halton sequence
generator are both in my 35m Camera macros I posted a few months back.

Cheers,
Edouard.

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