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#### NAME

```       catan, catanf, catanl - complex arc tangents

```

#### SYNOPSIS

```       #include <complex.h>

double complex catan(double complex z);
float complex catanf(float complex z);
long double complex catanl(long double complex z);

```

#### DESCRIPTION

```       The  catan()  function  calculates  the  complex  arc tangent of z.  If y = catan(z), then
z = ctan(y).  The real part of y is chosen in the interval [-pi/2,pi/2].

One has:

catan(z) = (clog(1 + i * z) - clog(1 - i * z)) / (2 * i)

```

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

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

exit(EXIT_SUCCESS);
}

```

#### SEEALSO

```       ccos(3), clog(3), ctan(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                                   CATAN(3)
```