NAME

     atanh - inverse hyperbolic tangent function

SYNOPSIS

     #include <math.h>

     double atanh(double x);

DESCRIPTION

     The  atanh()  function  calculates  the  inverse  hyperbolic
     tangent  of x; that is the value whose hyperbolic tangent is
     x.  If the absolute value of x is greater than 1.0,  acosh()
     returns not-a-number (NaN) and errno is set.

ERRORS

     EDOM x is out of range.

CONFORMING TO

     SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO

     asinh(3), acosh(3), cosh(3),