Unix Man Pages - atan - arc tangent function

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NAME

atan, atanf, atanl - arc tangent function


#include <math.h> 

double atan(double  x ); 
float atanf(float  x ); 
long double atanl( long double  x ); 

Link with -lm.

The atan () function calculates the arc tangent of x; that is the value whose tangent is x.

The atan () function returns the arc tangent in radians and the value is mathematically defined to be between -PI/2 and PI/2 (inclusive).

SVr4, POSIX.1-2001, 4.3BSD, C89. The float and long double variants are C99 requirements.