Warp wrote:

> Greg M. Johnson <pte### [at] thecommononethatstartswithycom> wrote:
>> Then for some n, n<20, if I then go plot out the values of an as a
>> function of frame_number when rendered, one of those values would be a
>> straight line. One but surely not all.
> 
>   Sorry, I didn't understand that.
> 


I was trying to understand the response of a hetero_mf or similar function,
one that has a bunch of parameters.  (And I was trying to find one that
just plain looked cool as an isosurface.)   So I set the computer running
with a couple hundred frames, where the parameters that go into the
function were determined by use of povray's rand function.  I also had the
image print out all the parms on the image as a text object.

In looking back at the set, I first noticed that the images didn't seem to
have varied as much as I might have liked.  Then as I studied the
parameters that showed up on the screen all (as expected) were bouncing all
around all over the place.  One (maybe the 3rd or 5th) was monotonically
decreasing from frame to frame by a constant value.

In other words, if one were to plot the values of each of the half-dozen,
rand()-derived, parameters as a function of frame_number,  all jumped
around unpredictably (to the human eye).  One parameter would have been a
straight line. In other words, someone could predict the next frame by
subtraction, even if they didn't know how povray computed the rand().

The nth use of rand() in a frame was anything but random if the seed were 
simply the frame_number.  I apologize I forget which n it was.

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