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

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, G_floating
    access:       write only
    mechanism:    by value

    Imaginary part of the input complex-number. MTH$AIMAG returns
    an F-floating number. MTH$DIMAG returns a D-floating number.
    MTH$GIMAG returns a G-floating number.