cacos(3) Library Functions Manual cacos(3)

# NAME¶

cacos, cacosf, cacosl - complex arc cosine

# LIBRARY¶

Math library (libm, -lm)

# 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 were added in glibc 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

# STANDARDS¶

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

# EXAMPLES¶

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