[Sollya-users] Desappointing behaviour

Valérie Ménissier-Morain Valerie.Menissier-Morain at lip6.fr
Fri Jul 18 17:51:14 CEST 2014


I am doing tests with classical examples of bad floating point behaviour
with Sollya.
For Rump quasi-polynomial
> a = 77617; b = 33096;
> 333.75*b^6 + a^2* (11*a^2*b^2 - b^6 - 121*b^4 - 2) + 5.5*b^8 + a/(2*b);
Warning: rounding has happened. The value displayed is a faithful rounding
to 165 bits of the true result.
-0.82739605994682136814116509547981629199903311578438
the result is fine but for Muller sequence
a = proc (n) { var r1, r2, res;
  r1:=11.0/2.0;
  r2:=61.0/11.0;
  match n with
  0: { res:=r1; }
  1: { res:=r2; }
  default: {
  for i from 2 to n do {
    res:=111.0-(1130.0-3000.0/r1)/r2;
    r1:=r2;
    r2:=res;
    };
  };
  return res;
};
a(100);
100
the result is the attended floating point value but with no information
about the fact that lots of rounding operations occured and that the result
is error prone. How  can I use Sollya for a better behaviour?

Valérie
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