VMS Help RTL Routines, MTH$, MTH$xREAL, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 complex-number

    OpenVMS usage:complex_number
    type:         F_floating complex, D_floating complex, G_floating
                  complex
    access:       read only
    mechanism:    by reference

    The complex number whose real part is returned by MTH$xREAL. The
    complex-number argument is the address of this floating-point
    complex number. For MTH$REAL, complex-number is an F-floating
    complex number. For MTH$DREAL, complex-number is a D-floating
    complex number. For MTH$GREAL, complex-number is a G-floating
    complex number.