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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Array of Variant Records Question...
Date: 1999/09/23
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Date: 1999-09-23T00:00:00+00:00
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In article <37E922DE.9007776F@mitre.org>,
  "Robert I. Eachus" <eachus@mitre.org> wrote:
> Robert A Duff wrote:
>
> > I don't know much about the theory of these things, but I
was under the
> > impression that Random can never ever return the same value
twice in a
> > row.  Robert Eachus or somebody can tell us for sure.
>
>    See previous post.  There is a major distiction here
between a
> floating-point generator and an integer or fixed-point
generator.  In an
> idealized enivronment, a floating-point generator would have
zero chance
> of
> returning the same value twice in a row.

You mean "real" instead of "floating-point", please do not use
floating-point to mean the real numbers of mathematics, they
are quite different. The term floating-point should be reserved
to computer number systems, which are not in any sense
non-ideal. They have well defined semantics which just happen
to be different from those of real arithmetic.

Since we never have real arithmetic on computers, talking about
this case is a red herring that has nothing to do with anything
we are interested in here.


> But in a computer environment where
> floating point values are represented by a finite set of
values, there
> should be a small but finite probability that two succesive
values are
> the same.

Yes, and that is what is important, and to say it again, there
is nothing "non-ideal" about this situation. Thinking of
computer floating-point as a non-ideal approximation of
real arithmetic is helpful only at a very simple level of
abstraction, and is not useful for serious numeric work.



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