# catan(3) — Linux manual page

```CATAN(3)                Linux Programmer's Manual               CATAN(3)
```

## NAME         top

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

## SYNOPSIS         top

```       #include <complex.h>

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

Link with -lm.
```

## DESCRIPTION         top

```       These functions calculate 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         top

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

## ATTRIBUTES         top

```       For an explanation of the terms used in this section, see
attributes(7).

┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface                             │ Attribute     │ Value   │
├──────────────────────────────────────┼───────────────┼─────────┤
│catan(), catanf(), catanl()           │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
```

## CONFORMING TO         top

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

## EXAMPLES         top

```       /* 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);
}
```

## SEE ALSO         top

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

## COLOPHON         top

```       This page is part of release 5.13 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.

2021-03-22                       CATAN(3)
```

Pages that refer to this page: atan(3)ctan(3)complex(7)