VMS Help DCX Routines, DCX$ANALYZE_INIT, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The DCX$ANALYZE_INIT routine initializes the context area for a
    statistical analysis of the data records to be compressed. The
    first (and typically the only) argument passed to DCX$ANALYZE_
    INIT is an integer variable to contain the context value. The DCX
    facility assigns a value to the context variable and associates
    the value with the created work area. Each time you want a
    record analyzed in that area, specify the associated context
    variable. You can analyze two or more files at once by creating a
    different work area for each file, giving each area a different
    context variable, and analyzing the records of each file in the
    appropriate work area.