Re: various observations (added to list)

[Daniel J S. <dan...@ie...>]

Ethan A Merritt wrote:
> On Thursday 11 May 2006 07:33 pm, Daniel J Sebald wrote:
> 
>>Well, it depends.  Here is what the gnuplot code says:
>>
>>     This is a transcription from Pascal to Fortran of routine
> 
> 	[...]
> 
> The fact that this comment is in a C program doesn't bother you?

Sort of.  But not too much, so long as someone tested it.

> In fact you *can* set the full 64 bits of the seed to something
> in particular if you want to.  This is even documented:
> 
>  `rand(0)`  returns a pseudo random number in the interval [0:1] generated
>             from the current value of two internal 32-bit seeds.
>  `rand({x,y})` for x>0 sets seed1 to x and seed2 to y
> 
> Note that rand(678) is not an example of this, since 678 is not a
> complex number.

From doc:

 `rand(x)`  for x>0 sets both seeds to a value based on the value of x.

> But since the documentation does not say what those
> two internal seeds will be used for, the reader is really no wiser than before.

:-)  Come on, this is getting to be semantics now.  Perhaps the documentation should be one of the following two to get rid of the confusion.

1)  rand({x,y})` for x>0 sets seed1 to x and seed2 to y, then generates a random number (which you can't really make much use of in a data stream) so that seed1 and seed2 become some other values.

This one can stay as it makes no promises in its wording:

 `rand(x)`  for x>0 sets both seeds to a value based on the value of x.

"a value based on" is sort of like "some people believe" (i.e., "this may not be factual").  So it is implying that seed1 = seed2 = x should be the result, but sure it could be interpreted as "it is whatever it is".  Which leads to...

2) `rand(x)`  for x>0 puts the PRNG in a known state
   `rand({x,y})` for x>0 puts the PRNG in a known state

Why go through the trouble of pointing out "seed1", "seed2" or "both seeds" in the documentation if it isn't accurate?

Dan