VMS Help RTL Routines, MTH$, MTH$CxABS, 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

    A complex number (r,i), where r and i are both floating-point
    complex values. The complex-number argument is the address of
    this complex number. For MTH$CABS, complex-number specifies
    an F-floating complex number. For MTH$CDABS, complex-number
    specifies a D-floating complex number. For MTH$CGABS, complex-
    number specifies a G-floating complex number.