atan2

atanh

#include <math.h>float atanhf(float arg);double atanh(double arg); long double atanhl(long double arg); 

atanh( ), atanhf( ), and atanl( ) were added by C99.

The atanh( ) family of functions returns the arc hyperbolic tangent of arg. This argument must be in the range –1 to 1; otherwise a domain error will occur. If arg equals 1 or –1 a range error is possible.

Related functions are acosh( ), asinh( ), sinh( ), cosh( ), and tanh( ).