To: J3                                                     J3/19-190
From: Malcolm Cohen
Subject: Interp on NUM_IMAGES
Date: 2019-July-31


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NUMBER: F18/013
TITLE:  TEAM_NUMBER to NUM_IMAGES is ambiguous
KEYWORDS: NUM_IMAGES, teams
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

Consider

PROGRAM p
   n = NUM_IMAGES()
   n1 = MERGE(1,2,THIS_IMAGE()<2)
   n2 = MERGE(1,3,THIS_IMAGE()<3)
   FORM TEAM(n1,x)
   FORM TEAM(n2,y)
   IF (n1==1) THEN
     CHANGE TEAM (x)
       PRINT *,NUM_IMAGES(TEAM_NUMBER=1) !(A)
       PRINT *,NUM_IMAGES(TEAM_NUMBER=3) !(B)
     END TEAM
   END IF
END PROGRAM

According to 16.9.145 NUM_IMAGES, the TEAM_NUMBER argument
    "shall identify the initial team or a team whose parent is the
     same as that of the current team".

However, at (A), there are two teams with team number 1 and the same
parent, one created by the FORM TEAM with "n1", the other created by
the FORM TEAM with "n2".

At (B), there is only one team with team number 3 and the same parent
as the current team, however, it is not a "sibling" team in that it
was not created by the same FORM TEAM statement.

Referring to the definition of the term "team number" at 3.145.4:
    "-1 which identifies the initial team, or positive integer that
     identifies a team within its parent team"
which has the same flaw in that there could be multiple teams within
the parent team that have that number.

Q. Was TEAM_NUMBER in NUM_IMAGES, and the "team number" definition,
   intended to limit the identification to teams created by
   corresponding FORM TEAM statement executions?

ANSWER:

Yes, this is the intention.  Edits are provided.

Note: Perhaps the terminology should be "corresponding" executions,
      as execution on more than one image can hardly be the "same"
      execution.

EDITS:

[20:30] 3.145.4 team number, definition, change
        "within its parent team" -> "among its sibling teams"
        append a (normative) note
    "Note 1 to entry: Teams are siblings when they were created by
                      corresponding FORM TEAM statement executions."
        and index "sibling teams" here.
{This is using "sibling teams" informally.
 Should the indexing be of the singular?
 There are always no siblings or more than one, so...?}

[204:35] 11.6.9 FORM TEAM statement, p1,
         change "creates new teams"
         to     "creates a set of sibling teams"
         and index "sibling teams" here.
This makes that whole paragraph read:
    "The FORM TEAM statement creates a set of sibling teams whose
     parent team is the current team."

[401:24-25] 16.9.145 NUM_IMAGES, p3 Arguments, TEAM_NUMBER argument,
    Change
        "team whose parent is the same as that of the current team"
    to
        "sibling team of the current team"
    and index "sibling teams" here.
OPTIONAL
    After that change insert
        "(that is, created by a FORM TEAM statement execution
          corresponding to that which created the current team)".

This (without the optional parenthesised remark) makes that
whole argument read:
 "TEAM_NUMBER shall be an integer scalar. It shall identify the
  initial team or a sibling team of the current team."

SUBMITTED BY: Malcolm Cohen

HISTORY: 19-xxx    m219  submitted

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