Project

General

Profile

Design #636

Distinguish indets from symbols in coeffring in Use command

Added by John Abbott over 9 years ago. Updated over 3 years ago.

Status:
Rejected
Priority:
High
Assignee:
John Abbott
Category:
enhancing/improving
Target version:
CoCoA-5.4.0
Start date:
23 Oct 2014
Due date:
% Done:

100%

Estimated time:
0.66 h
Spent time:
0.65 h

Description

The use command assigns the top-level variables whose names match those of the symbols in the ring. The assigned values are the values of the symbols in the given ring.

Suggestion: if the ring is a polynomial ring then the indeterminates are assigned as they are now, while all other symbols are assigned as elements of the coeffring. This is reasonable only if we already have automatic mapping of ringelems.

Discuss!

Related issues

Related to CoCoA-5 - Feature #7: Automatic mapping between (some) ringsResolved2011-10-20

Related to CoCoA-5 - Design #635: Automatic mapping of RingElem (in operation with a compound value)Closed2014-10-22

Related to CoCoA-5 - Design #634: Symbol in the coeff ringRejected2014-10-22

Related to CoCoA-5 - Design #637: Undesirable consequence of automatic mapping of RingElems?Closed2014-10-23

Related to CoCoALib - Design #1515: Indets in coeffring are ringelems in coeffring?Rejected2020-10-22

History

#1 Updated by John Abbott over 9 years ago

Consider the following scenario:

QQa ::= QQ[a];
P ::= QQa[x];
Use P;
deg(a); // will give 1
a2 := (x+a)-x;
a = a2; // true or false or error?
deg(a2); // must surely give 0, right?

Should a and a2 be considered as equal/equivalent in all contexts?

#2 Updated by John Abbott almost 9 years ago

  • Target version changed from CoCoA-5.1.2 summer 2015 to CoCoA-5.1.3/4 Jan 2016

#3 Updated by John Abbott about 8 years ago

  • Target version changed from CoCoA-5.1.3/4 Jan 2016 to CoCoA-5.?.?

I'm delaying this issue until some unspecified time in the future because it looks to be tricky to resolve.

The point is that in a ring such as QQ[a][x] CoCoA sees everything as a polynomial in just x, so a call such as deg(a^2,a) is seen as deg(coeff,coeff) which makes no sense (and so will produce an error). However an "advanced user" who understands this will have difficulty in effecting the desired computation...

The following will perform the desired computation

deg(LC(a^2), LC(a));

but it is not so clear to the reader what such a call should do. I would like to have something which makes it clear to the reader what the computation is... but how to achieve this?

The solution should work well regardless of the nesting depth of the rings: think of QQ[a][b][c][x,y,z] for instance.

#4 Updated by John Abbott over 3 years ago

  • Related to Design #1515: Indets in coeffring are ringelems in coeffring? added

#5 Updated by John Abbott over 3 years ago

  • Status changed from New to Rejected
  • Assignee set to John Abbott
  • Target version changed from CoCoA-5.?.? to CoCoA-5.4.0
  • % Done changed from 0 to 100
  • Estimated time set to 0.66 h

I am rejecting this. This issue is essentially duplicated in #1515.

Main reason for rejection is in comment 3 of issue #1515
Namely, too hard to interpret a "cleverly" in the ring QQ(a)[x] where 1/a must be allowed.

Also available in: Atom PDF