Re: Possible loss of accuracy

[marco atzeri]

Il 5/16/2013 1:07 AM, Stephen Montgomery-Smith ha scritto:
> OK guys, look at this.
>
> exp(2^50 * log(1-2^-50))
> ans =  3.6787944117144216749e-01
>
> (1-2^-50)^(2^50)
> ans =  3.6787944112862880353e-01
>
> So the problem is with the pow function, not the log or the exp.

as such is a problem in the libc providing the pow
function implementation

on cygwin octave 3.6.4, I have:

octave:1> format long e
octave:2> exp(2^50*log(1-2^-50))
ans =  3.67879441171442e-01
octave:3> (1-2^-50)^(2^50)
ans =  3.67879441171442e-01
octave:4> (1-2^-50)^(2^50)-exp(2^50*log(1-2^-50))
ans =  0.00000000000000e+00

regards
Marco