ccos() returns the cosine of a complex number, x + iy.

    ccos(x,y) is defined as cos (x + iy) = (cos x * cosh y - i * sin
    x * sinh y).

                           Entry-Point Names

    Generic
    Function   Data Type   OpenVMS        Tru64 UNIX
    Name       Required

    ccos       S_FLOAT     math$ccos_s    ccosf
               T_FLOAT     math$ccos_t    ccos
               X_FLOAT     math$ccos_x    ccosl
               F_FLOAT     math$ccos_f
               G_FLOAT     math$ccos_g