Subject: Maxima gives incorrect results with ceiling
From: Barton Willis
Date: Fri, 7 Dec 2007 10:46:12 -0600
As Andreas showed, the ceiling (and floor functions) do big float
evaluation using the current value of fpprec. This isn't ideal--it
would be better if the function pretty-good-floor-or-ceiling (defined
in src/nummod) had some logic in it that made a better choice for
fpprec. Even better would be big float interval evaluation (or my
favorite evaluation with a running error). This could be made nearly
foolproof, I think. Other Maxima functions (sign, for example) would
also benefit. Such things aren't all that difficult, but they take
time. Volunteers are welcomed!
Barton
maxima-bounces at math.utexas.edu wrote on 12/06/2007 06:58:43 PM:
> Hello,
>
> When working with large numbers and floating point arithmetic, maxima
> gives incorrect answers. For example,
>
> (%i5) ceiling(factorial(50)/exp(1));
> (%o5) 11188719610782480421414879249141773426630319613740326700720324608
>
> The correct result should be
> 11188719610782480504630258070757734324011354208865721592720336801 .
> What is the best way to go about fixing this issue?
>
> Thanks,
> Mike
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