atan

Syntax

#include <math.h> double atan(double x);

Description

This function computes the angle, in the range [-Pi/2..Pi/2] radians, whose tangent is x.

Return Value

The arc tangent, in radians, of x. If x is a NaN, the return value is NaN and errno is set to EDOM. If x is a positive or negative Inf, the return value is equal to positive or negative Pi/2, respectively, and errno is left unchanged.

Portability

ANSI/ISO C	C89; C99
POSIX	1003.2-1992; 1003.1-2001