#23193 closed enhancement (fixed)
some_elements is nondeterministic for function fields
Reported by:  saraedum  Owned by:  

Priority:  minor  Milestone:  sage8.0 
Component:  commutative algebra  Keywords:  sd86.5, sd87, beginner 
Cc:  Merged in:  
Authors:  Hanson Smith, Julian Rüth  Reviewers:  Julian Rüth, Freda Li 
Report Upstream:  N/A  Work issues:  
Branch:  3d8c354 (Commits)  Commit:  
Dependencies:  Stopgaps: 
Description
This should return some "typical" elements that are good for testing. Just random elements is a bit unfortunate because we are missing elements such as 0, 1, x, 1/x, …
sage: K.<x> = FunctionField(QQ) sage: K.some_elements() [(x^2  x  1)/(11/4*x^2  x), (x^2  1)/(x  1), (2/217*x^2 + 6*x  3)/(23*x^2  1/6*x  2)] sage: K.some_elements() [2*x  1/7, (x + 1)/(2*x^2 + 2/3*x + 1/8), (x^2 + x  1)/(1/3*x^2  1/2*x  35)]
Change History (18)
comment:1 Changed 3 years ago by
 Branch set to u/hwsmith/some_elements_is_non_deterministic_for_function_fields
comment:2 Changed 3 years ago by
 Commit set to d9e145d44c3e2e18e00409ff93620d4bee6141a2
 Status changed from new to needs_review
comment:3 Changed 3 years ago by
 Commit changed from d9e145d44c3e2e18e00409ff93620d4bee6141a2 to 59ecf9fce02b3507c037804a6a2b6f2c9a38eb14
comment:4 Changed 3 years ago by
 Commit changed from 59ecf9fce02b3507c037804a6a2b6f2c9a38eb14 to faf01bc63d8f844e1f7d6fc384d080e1248083cd
Branch pushed to git repo; I updated commit sha1. New commits:
faf01bc  Now, for function fields, some_elements gives a predetermined list of elements.

comment:5 Changed 3 years ago by
Sorry, I said something incorrect about this earlier, claiming that this would only affect rational function fields. This actually gets called as well for extensions of function fields, so you can never simply divide by the generator or something like that sadly.
Here is an idea how you could probably elegantly rewrite this and do so without putting some random constants in the code here. self._ring
is the polynomial ring underlying the function field (i.e., if you have K(x)
, then this would be K[x]
and if you have K(x)[y]/(f)
, then this would be K(x)[y]
.) So you could just take numerators and denominators from this ring, i.e., do two nested forloops (say a
, b
) that go through self._ring.some_elements()
, check whether self(b) != 0
and if so add self(a)/self(b)
to a list that you then return. What do you think?
You might want to also check that a != b
and a != 0
to avoid duplicates in that list and then add [0,1] to the list manually.
comment:6 Changed 3 years ago by
 Status changed from needs_review to needs_work
comment:7 Changed 3 years ago by
 Reviewers set to Julian Rüth
comment:8 Changed 3 years ago by
 Branch changed from u/hwsmith/some_elements_is_non_deterministic_for_function_fields to u/saraedum/some_elements_is_non_deterministic_for_function_fields
comment:9 Changed 3 years ago by
 Commit changed from faf01bc63d8f844e1f7d6fc384d080e1248083cd to 3d8c3546a27dc2d748eb8ca7059e758c498cfad9
Branch pushed to git repo; I updated commit sha1. New commits:
3d8c354  Return some_elements based on some_elements of a polynomial ring for function fields

comment:10 Changed 3 years ago by
 Status changed from needs_work to needs_review
comment:11 Changed 3 years ago by
 Keywords sd87 beginner added
comment:12 Changed 3 years ago by
 Reviewers changed from Julian Rüth to Julian Rüth, Freda Li
 Status changed from needs_review to positive_review
Doctests pass.
comment:13 Changed 3 years ago by
 Branch changed from u/saraedum/some_elements_is_non_deterministic_for_function_fields to 3d8c3546a27dc2d748eb8ca7059e758c498cfad9
 Resolution set to fixed
 Status changed from positive_review to closed
comment:14 Changed 3 years ago by
 Commit 3d8c3546a27dc2d748eb8ca7059e758c498cfad9 deleted
WARNING: this is causing the doctests of function_field to be VERY LONG (10 minutes) !
So please truncate this long list of some_elements to a much shorter list, until the doctest time is less than one minute.
See https://groups.google.com/forum/#!topic/sagerelease/mSHCqsHpdkA
comment:15 Changed 3 years ago by
I guess there was no reason to delete the commit here? Ok. Let's fix this in a followup ticket.
comment:16 Changed 3 years ago by
Hm...but there seems to be no way of putting the commit back in.
comment:17 Changed 3 years ago by
The commit deletion is automatic when editing a close ticket, and should not be a problem.
comment:18 Changed 3 years ago by
I created #23683 to speed up function field tests.
Branch pushed to git repo; I updated commit sha1. New commits:
Now, for function fields, some_elements gives a predetermined list of elements.