Re: Bug with g77 and -mieee on Alpha Linux

[Toon Moene <toon at moene dot indiv dot nluug dot nl>]

Richard Henderson wrote:

> On Thu, Jul 08, 1999 at 03:58:45PM -0000, craig@jcb-sc.com wrote:

> > Ah, well, it's good people can do that if they want, though the arguments
> > against -mieee being the default included "because it catches bugs in code",
> > which, presumably, silently mapping underflows to zero won't.

> Actually, most of the bugs are where you _start_ with denormals,
> typically because of uninitialized data.  UNZ doesn't stop trapping
> when the inputs are non-normal.

[ Thanks for reminding me that underflow always maps to zero on Alpha -
  keep forgetting that ]

Of course, I *still* think that a program generating denormals (and
getting underflow to zero) is wrong:  All of a sudden there's a number
in the algorithm that's treated as "normal" (while it is _de_normal) -
and now you can't divide by it.

I cannot glean inside Martin's nonlinear equations, but the following
description:

<QUOTE>
Perhaps, but while solving highly nonlinear sets of equations, like in
analog circuit simulators nearly anything can appear. Nobody knows,
where newton will bring you. You can decide to make smaller newton 
corrections only  a f t e r  you have the bad ones and thus you have to 
deal with these bad numbers somehow.
</QUOTE>

to *me* sounds like a grave mis-use of Newton-Raphson root finding.

You won't believe this, but I just opened Press et al's "Numerical
Recipes" at random:

Chapter 9  -  Root Finding and Nonlinear Sets of Equations

9.6 Newton-Raphson Method for Nonlinear Systems of Equations

We make an extreme, but wholly defensible, statement:  There are _no_
good, general methods for solving systems of more than one nonlinear
equation.  Furthermore, it is not hard to see why (very likely) there
_never_will_be_ any good, general methods: ...

Martin, proceed from there (pay special attention to 9.7 Globally
Convergent Methods for Nonlinear Systems of Equations).

Hope this helps,

-- 
Toon Moene (toon@moene.indiv.nluug.nl)
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
Phone: +31 346 214290; Fax: +31 346 214286
GNU Fortran: http://world.std.com/~burley/g77.html

PS: This is getting of-topic; for more help, the rate is $200 / hour :-)