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CACOS(3)                  (2020-06-09)                   CACOS(3)

NAME
cacos, cacosf, cacosl - complex arc cosine

SYNOPSIS
#include <complex.h>

double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);

DESCRIPTION
These functions calculate the complex arc cosine of z. If
y = cacos(z), then z = ccos(y).  The real part of y is cho-
sen in the interval [0,pi].

One has:

cacos(z) = -i * clog(z + i * csqrt(1 - z * z))

VERSIONS
These functions first appeared in glibc in version 2.1.

ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).  allbox; lbw28 lb lb l l l.
Interface Attribute Value T{ cacos(), cacosf(), cacosl()

CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

EXAMPLES

#include <complex.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
double complex z, c, f;
double complex i = I;

if (argc != 3) {
fprintf(stderr, "Usage: %s <real> <imag>\n", argv);
exit(EXIT_FAILURE);

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CACOS(3)                  (2020-06-09)                   CACOS(3)

}

z = atof(argv) + atof(argv) * I;

c = cacos(z);

printf("cacos() = %6.3f %6.3f*i\n", creal(c), cimag(c));

f = -i * clog(z + i * csqrt(1 - z * z));

printf("formula = %6.3f %6.3f*i\n", creal(f), cimag(f));

exit(EXIT_SUCCESS);
}