Subject: Re: mpi-context: context and group (medium)

From: L J Clarke <[email-masked]>
Date: Fri, 9 Apr 93 16:48:19 BST

Dear MPI Colleagues

This is a short letter. 

First: a colleague here pointed out to me that I left an unfinished
point, ie failed to draw to conclusion, in the mail message "Subject:
mpi-context: context and group (medium)".  Apologies to you all for my
slipshod work.  I conclude that discussion here. 

Regarding the process identifier, for which there are arguments for and
against its appearance as a global unique process identifier and as a
process local handle to opaque process descriptor object.  The
discussion in the referenced letter should have concluded that MPI
should say that it is a process local identifier of a process expressed
as an integer, and no more.  This allows the implementation of MPI to
choose the "best" form, which may be a global unique process identifier
or may be a process local opaque reference to a process description
object or may be an index into a table of subject objects describing all
processes. 

Second: the letter I sent to you all "Subject: mpi-context: comment and
suggestion" contained.  Apologies again.  I correct those errors here. 

* The claim that the conceptual framework of Tony regarding Group and 
  Context restricts the possibilities for inter(group)communication is 
  false.  It is the restriction of the message envelope to 
  (context,process,tag) which creates the limitation in this case.

* When I explained how intergroup communication can be done within the
  conceptual framework of Marc (Snir) I should have said that this 
  is a method for *simulating* intergroup communication without wildcard
  on group'.

* When I explained how intergroup communication can be done within the
  framework Tony Ishould have said that this is a method for
  *implementing* intergroup communication without wildcard on group'.

Final: Regarding the same letter whihc really deals with the subject of
inter(group)communication I may have made errors or at least unhelpful
assumptions in the latter couple of paragraphs of the message.  Again I
apologise.  I plan to go into deep thought on the subject of
inter(group,context)communication, and promise to deliver some quality
discussion to you all next week.  Please bear with me.  Until such time
I shall omit inter(group,context)communication from my discussions. 

Best Wishes
Lyndon

         /--------------------------------------------------------\
    e||) | Lyndon J Clarke    Edinburgh Parallel Computing Centre | e||) 
    c||c | Tel: 031 650 5021  Email: [email-masked]  | c||c 
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