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[Octave-bug-tracker] [bug #44310] log and functions which use log return
From: |
Michael Godfrey |
Subject: |
[Octave-bug-tracker] [bug #44310] log and functions which use log return incorrect result |
Date: |
Wed, 25 Feb 2015 22:40:46 +0000 |
User-agent: |
Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0 |
Follow-up Comment #5, bug #44310 (project octave):
I left out what I meant to include "below"
That is:
++
#include <stdio.h>
#include <complex.h>
#include <math.h>
int main(void)
{
float complex z = catanh(0-10i);
printf("catanh(0-10i) = %e%+ein", creal(z), cimag(z));
double complex x = (0-10i);
double complex xm = (1.0 - x);
double complex xp = (1.0 + x);
double complex an = clog(xp/xm)/2.0;
long double complex anl = clogl(xp/xm)/2.0;
double complex ans = (clog(xp) - clog(xm))/2.0;
printf("catanh (an) = %e%+ein", creal(an), cimag(an));
printf("catanh (anl) = %e%+ein", creal(anl), cimag(anl));
printf("catanh (ans) = %e%+ein", creal(ans), cimag(ans));
}
which gives:
catanh(0-10i) = 0.000000e+00-1.471128e+00i
catanh (an) = 4.671731e-17-1.471128e+00i
catanh (anl) = 4.671731e-17-1.471128e+00i
catanh (ans) = 0.000000e+00-1.471128e+00i
--
This shows that clog(xp) - clog(xm) yields a different
and correct answer instead of clog(xp/xm)
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