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

 complex-number

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

    A complex number (r,i), where r and i are floating-point numbers.
    The complex-number argument is the address of this complex
    number. For MTH$CSIN, complex-number specifies an F-floating
    complex number.