# catan (3) - Linux Man Pages

## 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);

Link with -lm.

## DESCRIPTION

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

These functions first appeared in glibc in version 2.1.

## ATTRIBUTES

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

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

## 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);
exit(EXIT_FAILURE);
}

z = atof(argv) + atof(argv) * 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); }

## COLOPHON

This page is part of release 5.05 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/.

## SEE ALSO

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