On Mon, Oct 28, 2002 at 12:28:39PM -0600, Nathan Straz wrote:
> >
> > The AIM7/AIM9 new_raph is broken code. The convergence loop termination
> > conditional looks something like:
> > if (delta == 0) break;
> > for a type "double" delta. You ought to change that to be something
> > like:
> > if (delta <= 0.00000001L) break;
>
> I usually specify the compiler flag -ffloat-store and that fixes the
> issue for me.
Maybe that will work as a work-around. But it is nothing but a
work-around. The previous poster was right - the code is broken.
The "==" operator usually doesn't have any reasonable use on floating
point values (yes there are cases where it makes sense, but this is not
one of them).
A result from any computation on double values cannot be assumed to
"equal" anything in particular. Zero included.
The correct way to terminate that loop is, like was already suggested,
doing a comparison to see if the residual is "numerically zero" or
"sufficiently zero-ish for the given purpose". Eg. "delta < 1E-12" or
eventually "fabs(delta) < 1E-12".
Comparing to zero makes *no* sense. It's written by someone who has no
understanding of numerics (or perhaps just didn't think clearly at that
moment - /me trying not to insult more people than strictly necessary ;)
--
................................................................
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:.........................: putrid forms of man :
: Jakob Østergaard : See him rise and claim the earth, :
: OZ9ABN : his downfall is at hand. :
:.........................:............{Konkhra}...............:
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This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:40 EST