SYNOPSIS

#include <complex.h>

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

Link with -lm.

DESCRIPTION

These functions calculate the complex arc cosine of z. If y = cacos(z), then z = ccos(y). The real part of y is chosen 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).

Interface	Attribute	Value
cacos(), cacosf(), cacosl()	Thread safety	MT-Safe

CONFORMING TO

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

EXAMPLE

/* Link with "-lm" */
#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[0]);
        exit(EXIT_FAILURE);
    }
    z = atof(argv[1]) + atof(argv[2]) * 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);
}

COLOPHON

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