[Shootout-list] Mandelbrot Set for CMUCL and SBCL 2nd try

[Greg Buchholz]

--- Pascal Obry <pascal@obry.net> wrote:
> 
> Greg,
> 
>  >     Try chaning line 35 from...
>  > (when (not (dotimes (n 50)
>  > ...to...
>  > (when (not (dotimes (n 51)
> 
> I tried something like that for the Ada bench. It turns out that
> swaping some
> lines to do the computation and test in the very same way as C did fix
> the
> problem. Yet I think this is not a good solution.

   With some very well reasoned argument, you might be able to convince
me that we shouldn't require our floating point benchmarks to be
implemented the same.  But not wanting to correct a fence post error is
not one of those arguments.  And I think any die-hard numerical guy would
scoff at a language which wouldn't allow him to implement his algorithm
correctly.  The root problem is that fixed precision floating point math
is neither distributive nor associative, so you can't order your
calculations willy-nilly and expect the same answer.  So the question is,
should the shootout require absolute exactness, or should we allow a
little bit of roundoff error caused by the common misconception that our
floating point hardware is infinitely precise?  It's an interesting
question that the shootout needs to decide.

Faithfully,

Greg Buchholz


P.S.  A well reasoned argument might consist of stating that the
mandelbrot set isn't well-conditioned or numerically stable.  But that
doesn't address the question about the other floating point benchmarks. 
Also note that there are currently 20 programs which are able to produce
the exact result on the mandelbrot test.




		
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