Provided by: manpages-dev_3.35-0.1ubuntu1_all #### NAME

```       cacosh, cacoshf, cacoshl - complex arc hyperbolic cosine

```

#### SYNOPSIS

```       #include <complex.h>

double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);

```

#### DESCRIPTION

```       The   cacosh()   function   calculates  the  complex  arc  hyperpolic  cosine  of  z.   If
y = cacosh(z), then z = ccosh(y).  The imaginary part of  y  is  chosen  in  the  interval
[-pi,pi].  The real part of y is chosen nonnegative.

One has:

cacosh(z) = 2 * clog(csqrt((z + 1) / 2) + csqrt((z - 1) / 2))

```

#### VERSIONS

```       These functions first appeared in glibc in version 2.1.

```

#### CONFORMINGTO

```       C99.

```

#### 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;

if (argc != 3) {
fprintf(stderr, "Usage: %s <real> <imag>\n", argv);
exit(EXIT_FAILURE);
}

z = atof(argv) + atof(argv) * I;

c = cacosh(z);
printf("cacosh() = %6.3f %6.3f*i\n", creal(c), cimag(c));

f = 2 * clog(csqrt((z + 1)/2) + csqrt((z - 1)/2));
printf("formula  = %6.3f %6.3f*i\n", creal(f2), cimag(f2));

exit(EXIT_SUCCESS);
}

```

#### SEEALSO

```       acosh(3), cabs(3), ccosh(3), cimag(3), complex(7)

```

#### COLOPHON

```       This  page  is  part of release 3.35 of the Linux man-pages project.  A description of the
project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
pages/.

2011-09-15                                  CACOSH(3)
```