Re: [Maxima-discuss] Floating point overflow: what to do?

[Jorge C. <Jor...@av...>]

Hi there!

I was doing a little exploration of underflow errors -- mostly to explain the IEEE-754 standard to my students -- and noticed that in some cases, underflows are handled differently based on the underlying platform.  For instance,  found that 4e-324 (entered straight from the prompt) rounds down to 0.0 in a Mac, up to 4.94065… x 10^-324 in older Windows machines, and is converted to the fixed-point number 4.0d-324 in Linux and newer Windows machines.  It's really the underlying Lisp that seems to make a difference, but my point is that I don't know that any one of these behaviors is preferable over the others.  Would your plan be to force conversion to bigfloats in place of any of these choices?

Somewhat ambivalent...

Jorge

Richard Fateman <fa...@be...<mailto:fa...@be...>> writes:
What about underflow?   It seems to me it would be distressing if  x^2
overflows to bigfloat
but  the mathematically equal quantity computed as    1/(1/x)^2 is a
divide-by-zero.

Rupert Swarbrick <rsw...@gm...<mailto:rsw...@gm...>> writes:

Hmm, good point.

Although 1/(1/x) != x for floating x anyway:

 (%i46) block([a: 1/x], 1/a - x), x=0.123;
 (%o46)                      - 1.387778780781446e-17

(The nonsense with block() is to avoid the simplifier setting the
expression to zero ahead of time.)

Anyone got any ideas? Do we trap underflows at the moment?


Rupert


--
Dr. Jorge Alberto Calvo
Associate Professor of Mathematics
Department of Mathematics and Physics
Ave Maria University

Phone: (239) 280-1608
Email: jor...@av...<mailto:jor...@av...>
Web: http://sites.google.com/site/jorgealbertocalvo