CATAN(3) | Library Functions Manual | CATAN(3)

# NAME

`catan`, `catanf`, `catanl` — complex circular arc tangent

# SYNOPSIS

Math Library (libm, -lm)
`#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`(), `catanf`() and `catanl`() functions compute the complex circular arc tangent of z.

If z = x + iy, then

    Re catan(z) = 1/2 * atan(2x / (1 - x^2 - y^2)) + k Pi.
    Im catan(z) = 1/4 * log((x^2 + (y + 1)^2) / (x^2 + (y - 1)^2)).

# RETURN VALUES

The `catan`(), `catanf`() and `catanl`() functions return the complex circular arc tangent of z with unbounded imaginary part, and real part in the interval [-Pi/2, Pi/2].

# SEE ALSO

cacos(3), casin(3)

# STANDARDS

The `catan`(), `catanf`() and `catanl`() functions conform to ISO/IEC 9899:1999 (“ISO C99”).

June 7, 2025 | Debian