AIPS HELP file for PARALLEL in 31DEC25

As of Wed Mar 26 14:25:43 2025

INPUTS

          The number of processors to be used for parallelized
          AIPS programs is given as the immediate argument.

HELP SECTION

PARALLEL
Type: Verb
Use:  PARALLEL(p) will interpret its immediate argument as the number
      of processors that will be used by AIPS tasks that have been
      enabled for parallel processing.  This will not have any effect
      on tasks that have not been specifically compiled to use multiple
      processors or on tasks that are already running.
         In general, large problems benefit from having more processors
      working on them but you may experience substantial slow-downs if
      you set p (the number of processors too large).  In preparing for
      a long run (which is where parallel processing is most worth
      while) it is often useful to select a small subset of your data
      that can be processed in a few minutes and experiment with
      different values of p to find the fastest option.  Task-specific
      explain files may give more detailed advice.
         The following rules of thumb may be helpful.
         - Keep p = 1 unless you are reasonably sure that parallel
           processing will help with the problem that you are dealing
           with.
         - If your machine has n processors limit p to n-1 so that one
           processor is free to handle the AIPS command-line processor
           and other functions (most parallel FORTRAN systems suffer
           badly if they have to share processors with other programs).
         - Reduce the number of processors if you are sharing a machine
           with other users.
      Special cases:
         PARALLEL(0): (or no argument) show the current number of
                     processors that will be used by parallel tasks.
Adverbs:  The immediate argument is the number of loGical processors.
      No actual adverbs.

EXPLAIN SECTION