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```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);

```

## DESCRIPTION         top

```       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         top

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

## CONFORMING TO         top

```       C99.
```

## EXAMPLE         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);
}
```

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

## COLOPHON         top

```       This page is part of release 3.51 of the Linux man-pages project.  A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.

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