NAME
SYNOPSIS
DESCRIPTION
VERSIONS
ATTRIBUTES
CONFORMING TO
EXAMPLE
SEE ALSO
COLOPHON

## 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);

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).

## 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);
}

## SEE ALSO

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

## COLOPHON

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