SIFT

Programs

Percy

Syntax

     LET @name = @name SIFTED THROUGH @name
 
     LET @name = @name SIFTED INSIDE @name

     LET @name = @name <= @name
 
     LET @name = @name < @name

Description

The SIFT command reduces the number of intervals in a schedule by `sifting them through' the intervals in a second schedule. That is, each interval in the first schedule is retained only if it is contained by one of the intervals in the second schedule.

The SIFTED THROUGH

A graphical description of the SIFT command is shown below.

   First schedule  :      ---     ---------  --   --   ----- -   ---
   Second schedule :   -------    ----        --- --    --------------
   Output schedule :      ---                     --         -   ---

Examples

In the following example, the schedule COMPLETE contains intervals corresponding to several complete events (for example, stellar occultations). The schedule CONSTRAINTS contains intervals meeting other (planning or operational) constraints.

Pounding COMPLETE through CONSTRAINTS yields the collection of complete event intervals for which the constraints are satisfied.

   RESTORE schedule COMPLETE    from file COMPLETE_EVENTS.WIN;
   RESTORE        CONSTRAINTS           CONSTRAINTS_MET.WIN;
 
   SIFT  COMPLETE through CONSTRAINTS to yield POSSIBLE;
 
   STORE schedule POSSIBLE in file POSSIBLE_EVENTS.WIN;

Notes

The SIFT command is similar to the INTERSECT command in that the output schedule contains only points that are contained in both of the input schedules. However, SIFT is not symmetric (the order of the schedules is significant); and the intervals in the input schedule may be removed, but are never shortened.

Related Topics

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3. The Percy Help System