VMS Help RTL Routines, MTH$, MTH$xIMAG, 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 input complex number. The complex-number argument is the
    address of this floating-point complex number. For MTH$AIMAG,
    complex-number specifies an F-floating number. For MTH$DIMAG,
    complex-number specifies a D-floating number. For MTH$GIMAG,
    complex-number specifies a G-floating number.