asinh()
    returns the hyperbolic arc sine of x for x in the interval
    [-infinity, +infinity]. asinh(x) = ln(x + sqrt(x**2 + 1)).

    asinh() is the inverse function of sinh().  asinh(sinh (x)) = x.

                           Entry-Point Names

    Generic
    Function   Data Type   OpenVMS        Tru64 UNIX
    Name       Required

    asinh      S_FLOAT     math$asinh_s   asinhf
               T_FLOAT     math$asinh_t   asinh
               X_FLOAT     math$asinh_x   asinhl
               F_FLOAT     math$asinh_f
               G_FLOAT     math$asinh_g