[Octave-bug-tracker] [bug #44310] log and functions which use log return incorrect result

[Michael Godfrey]

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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