Ciao, on the GNU Scientific Library mailing list I asked the following:
>for some values of the operand I get different >results from 'acosh' when using GSL (1.8), Guile (1.8) >and GNU Octave (2.1.63). Other functions give me >different results, too. [...] > >Browsing Wikipedia for acosh formulas it seems to me >that GSL is using an equivalent of: > > (log (- x (sqrt (- (* x x) 1)))) > >while the others are using an equivalent of: > > (log (+ x (sqrt (- (* x x) 1)))) > >I'm interested in having equal results from GSL >and Guile, [...] and got the following reply: >There are different branch cut conventions used >by different programs. acosh or other inverse >functions are mutiple-valued functions so the >result is not uniquely defined. > >GSL uses one of the two common conventions >(W.Kahan's) because it has better consistency with >IEEE arithmetic. It is also used by Common >Lisp -- see the GSL Reference manual for details and >references. The others are using a different >convention (Abramowitz & Stegun). As such, all the >answers are correct. So, do you suggest me to override the GSL function to make it equal to the Guile one, or vice versa? -- Marco Maggi "They say jump!, you say how high?" Rage Against the Machine - "Bullet in the Head" _______________________________________________ Guile-user mailing list [email protected] http://lists.gnu.org/mailman/listinfo/guile-user
