Re: entropy

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Tim:
>> One of my very old computers had a white noise generator for use by
>> the random number function.  One day I decided to test it by
>> repeatedly polling it and using alternate polls as X and Y
>> co-ordinates to place a mark on a graph.  The images was,
>> predominately, two fat parallel diagonal bars.  The effect was
>> rapidly noticeable, and didn't even out over a prolonged time.

Les:
> I can see this happening even with some kinds of "cosmic" number
> generators.  Even the friendly neighborhood geiger counts can be
> affected by environment and yield less than optimal noise.  However
> there are some quite good white noise diodes available from commercial
> houses that do considerable analysis of their noise results, and will
> yield quite good histogram distributions and even multi-axis
> distributions.  However the experiment you did was a bit biased in its
> setup if you modified the output to generate the two axis, for example
> limiting the binary data to say 8 bit numbers, they you essentially
> get a distribution running from 0-511 which would have a gaussian
> curve if the random numbers were uniform.

Using psuedo code, what it did was:

  x = random number between 1 and 200
  y = random number between 1 and 200
  draw dot at x,y
  repeat

Now, considering that the random number is generated from white noise,
there is no way for me to affect *how* the number is generated, all I
can do is specify a range (there is no reseeding control for something
that's generated from an uncontrolled white noise source), nor should
any of my program code really be able to affect the random number, I
expected that I'd get a random snow pattern drawn up over time.

I repeated the experiment on a later computer, and it did what I
expected.  The dots were apparently randomly drawn, and eventually
filled up all the space.  I don't know how that computer (a Z80 based
VZ300) generated its random numbers, though.

It's, now, years since I studied statistics in maths classes, but I
don't recall any good reason why my first experiment should not have
been been just the same as the second one.  A random number is a random
number...

-- 
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