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Synopsis:
    #include <math.h>
    double atanh( double x );

Description:
    The atanh function computes the inverse hyperbolic tangent of x.  A
    domain error occurs if the value of x is outside the range (-1,1).

Returns:
    The atanh function returns the inverse hyperbolic tangent value.  When
    the argument is outside the permissible range, the  matherr function is
    called.  Unless the default  matherr function is replaced, it will set
    the global variable  errno to  EDOM, and print a "DOMAIN error"
    diagnostic message using the  stderr stream.

See Also:
    acosh, asinh, matherr, tanh

Example:
    #include <stdio.h>
    #include <math.h>

    void main()
      {
        printf( "%f\n", atanh( 0.5 ) );
      }

    produces the following:

    0.549306

Classification:
    WATCOM

Systems:
    All