(j3.2006) RANDOM_INIT question

[Keith Bierman]

For the case with REPEATABLE=.false. how would any meaningful test be able
to tell the difference between use of the PRNG generator used in the
REPEATABLE=.true. case vs. any other PRNG or the hardware device Bill
speaks of?

Keith Bierman
khbkhb at gmail.com
kbiermank AIM
303 997 2749

On Mon, Sep 21, 2015 at 10:13 PM, Bill Long <longb at cray.com> wrote:

> OK.  I?ll keep a copy of this email for future use when questions arise.
>
> I do think it would be at least a good idea to link what RANDON_INIT does
> to RANDOM_NUMBER.  In the description of RANDOM_SEED, we specify "The
> pseudorandom number generator used by RANDOM_NUMBER?.  We should make the
> ?used by RANDOM_NUMBER? connection in RANDOM_INIT as well.   That would
> close the loop to connect RANDOM_INIT to the description of RANDOM_SEED
> where the requirement of the ?same sequence? is stated.
>
> Cheers,
> Bill
>
>
> On Sep 21, 2015, at 7:16 PM, Malcolm Cohen <malcolm at nag-j.co.jp> wrote:
>
> > <<<
> >  Since ?repeatable?  can be used to describe whether a generator would
> > generate the same sequence given a particular starting seed,  there is
> > possibility of confusion.
> >>>>>
> >
> > There is no confusion in the standard.
> >
> > The actual words in the standard
> > (a) explicitly specify that this is a pseudo-random number generator,
> not a
> > (scare quotes) "true random" generator;
> > (b) explicitly specify that a particular seed, (actual quote) "shall
> result
> > in the same sequence of pseudorandom numbers being generated";
> > (c) explicitly specify that REPEATABLE=.FALSE. merely sets the seed
> (actual
> > quote) "to a processor-dependent, unpredictably different value on each
> > call".
> >
> > There is no ambiguity here!
> >
> > <<<
> >  A Note to say that there is only one generator, and we don?t mean that
> > usage of ?repeatable?,  might be clarifying.
> >>>>
> >
> > We have Already Fully Specified *Precisely* what the effect of the
> *Argument
> > Whose Name Is "REPEATABLE"* is.
> >
> > In fact we do not use the word "repeatable" ***ANYWHERE IN THE ENTIRE
> > STANDARD***.  Not even once.  Not here, and not anywhere else either.
> The
> > argument name is REPEATABLE, that's it.  And I repeat, the semantics are
> > Fully Specified.
> >
> > Such a note, following the text which actually Specifies The Semantics
> > Normatively, would not only be completely unnecessary but also
> > counter-productive.  One might as well word it as "You might think that
> you
> > can ignore the semantics we've just specified, because you went into an
> > entire imaginary world based on the spelling of the argument name, but
> you
> > would be wrong."
> >
> > There is simply No Case To Answer here.
> >
> > Grumpily,
> > --
> > ..............................The Editor.
> >
> > _______________________________________________
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> > J3 at mailman.j3-fortran.org
> > http://mailman.j3-fortran.org/mailman/listinfo/j3
>
> Bill Long
>      longb at cray.com
> Fortran Technical Support  &                                  voice:
> 651-605-9024
> Bioinformatics Software Development                     fax:  651-605-9142
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>
>
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