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George J. Wallace wrote:
> Thank you Very Much. I was trying to use the value in rand() like a
> subscript and it kept spitting up. Thanks again for the explanation...gjw
> "Slime" <fak### [at] email address> wrote in message
> news:45a31c20$1@news.povray.org...
>
>> [...]
>>
>>Think of colorSeed as a list of random numbers, and rand(colorSeed) always
>>gets the next one. If you want to start over, you just #declare colorSeed
>>again in the same way. My guess is that the stream is about 2^32 numbers
>>long, which is long enough that you'll never hit the end of it (and if you
>>do it will just loop back to the beginning).
>>
Actually, it's not a 'real' list (like an array). It's an algorithm
that calculates a new (pseudo) random number each time it's used, based
on the previously calculated number -- or the given seed in the case of
the first call.
As to Slime's guess of 2^32 numbers, this would be true if the algorithm
is based on 32-bit integers. But since it returns floating point
values, it may be that the algorithm is based on floating point numbers
-- and that the total number of possible values could be much higher. I
don't know how the rand() function is actually implemented in POV-Ray,
so I can't say one way or another. Of course, as a practical matter,
whatever it is, the number of possible values is 'enough'.
Naturally, if you want to think of this as a list or array, that's fine
too. It doesn't really matter how you visualize it as long as you learn
to use it properly.
Now, a completely irrelevant side note: I once wrote a floating point
random number generator for my personal C-language function library.
(The standard C function libraries already have an integer version.)
Although I'm not a good enough mathematician or statistition to really
know the quality of my function, it was good enough for my (limited)
uses. (I'm just a hobby-programmer, not a professional -- and I haven't
done much programming at all for some time.)
-=- Larry -=-
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