cacos(3) Library Functions Manual cacos(3)

cacos, cacosf, cacosl - complex arc cosine

Math library (libm, -lm)

#include <complex.h>
double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);

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))

For an explanation of the terms used in this section, see attributes(7).

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

C11, POSIX.1-2008.

glibc 2.1. C99, POSIX.1-2001.

/* Link with "-lm" */
#include <complex.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
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]);
    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));

ccos(3), clog(3), complex(7)

2024-05-02 Linux man-pages 6.8