Re: terrible bug in Mathematica (//N), but why????

 There is nothing whatsoever
to say that the expression AFTER fullsimplify might
also be quite wrong. There are many books on numerical
analysis...

If you want something "automatic" to happen, you might
try, in Mathematica..
N[xxxxx,50]   to try to get 50 decimal digits for xxxxx
instead of
N[xxxxx]  which will use machine precision, and will be
be faster but of unknown accuracy.

As for differences with m being 43 instead of 44...
Sin(2*n*pi) is 0  and Sin((2*n+1)*pi)  is 1. Such
things are hardly random :)

RJF


symbio wrote:

Dear Richard,
can you explain how such huge error occurs if FullSimplify is not used? one case gives x10^25, the other with fullsimplify gives x10^-41 (or almost zero). Does this mean that fullsimplify should be applied to ALL numeric calculations before //N evaluate is applied? It seems very random, specially if you change the m and n from 43 to 44 or 42, you don't get that error!! how do you explain that?

.

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