Feature #1763: implement ideal(R) for zero ideal, with no generators? - CoCoALib - CoCoA Project

Feature #1763

implement ideal(R) for zero ideal, with no generators?

Added by Anna Maria Bigatti 8 months ago. Updated 2 months ago.

Status:

Rejected

Priority:

Normal

Assignee:

Anna Maria Bigatti

Category:

New Function

Target version:

CoCoALib-0.99850

Start date:

07 Sep 2023

Due date:

% Done:

100%

Estimated time:

1.01 h

Spent time:

0.90 h

Description

I'm fairly sure we used to have the constructor ideal(R) for an ideal with no generators, but I cannot find any trace of it (and/or why we do not have it).
Of course we can write explicitely ideal(R, v) with an empty vector, but that's ugly.

Should I add the constructor ideal(R)?

2024-02 No longer needed: just call ideal(zero(R))

Related issues

History

#1 Updated by John Abbott 8 months ago

Mmm, don't remember... I'm still on holiday (sort of).
We can do ideal(zero(P)) and ideal(P,EmptyList).
Maybe the argument was that ideal(P) is less clear to read than either of the alternatives in the line above?

Do we have good "use cases" where someone really want to create a zero ideal with no generators rather than than a zero ideal containing one zero generator?

We could also consider making a new function NonZeroGens; it'd be easy to make, but would it ever really be useful?

#2 Updated by John Abbott 8 months ago

Here is another idea. We could create a constant empty vector of RingElem, and use that.

  const std::vector<RingElem> NoGens;
  ...
  ideal(P, NoGens); // since NoGens is empty it works for all rings P

This is probably good for readability, but it does create a new global object.
It is also similar to what one must do in CoCoA-5: namely ideal(P,[])

#3 Updated by John Abbott 7 months ago

In comment 1 I used EmptyList; in comment 2 I used NoGens
I think I dislike EmptyList because it is rather ambiguous: it should be EmptyListOfRingElem (but who wants to write/read that?)
NoGens is short, but reads well only in a context where "generators" are needed. Might we need an empty list of RingElem in any other context?

#4 Updated by John Abbott 4 months ago

Target version changed from CoCoALib-0.99800 to CoCoALib-0.99850

I still think that ideal(P) looks odd, and is less immediate to understand than ideal(P,EmptyListOfRingElem).
Or we could just create a new function ZeroIdeal(P).
What do you think?