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# cacos(3)

2019-03-06
Aliases: cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosf(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3), cacosl(3)

### manpages-dev

Manual pages about using GNU/Linux for development

### man-pages

Linux kernel and C library user-space interface documentation

## 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 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 Thread safety MT-Safe

## CONFORMING TO

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

## EXAMPLE

#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); }