change for p-adic rings

[xcaruso]

Started as a proposal to change precision of rings, this is now a more general change method.

Depends on #23331

CC: @saraedum @roed314

Component: padics

Keywords: precision

Author: David Roe

Branch/Commit: 86b58de

Reviewer: Julian Rüth, Xavier Caruso

Issue created by migration from https://trac.sagemath.org/ticket/20310

[xcaruso]

comment:1

As discussed in Sage Days 71, I tried to implement this method using the construction functor but it seems that the latter is only defined for Zp or Qp but not for extensions.
So, what should I do? Implement the methods construction as well? Something else?

[xcaruso]

Branch: u/caruso/change_precision

[roed314]

Commit: 9ca8df8

[roed314]

comment:3

Implementing construction is a good idea anyway, since they're used in coercion. And until we change extensions to be defined by exact polynomials, you'll need to raise the precision of the base ring as well, so it's probably necessary.

---

New commits:

9ca8df8

Generic function change_precision

[roed314]

Changed branch from u/caruso/change_precision to u/roed/change_precision

[sagetrac-git]

Changed commit from 9ca8df8 to 53d2446

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e16f79f	Add construction method for extensions of p-adic rings and fields, switch implementation of fraction_field and integer_ring
a88b630	Fixing problems revealed by tests
fdd03cb	Merge branch 'u/roed/padic-floats' of git://trac.sagemath.org/sage into t/20310/change_precision
53d2446	Added ability to edit show_prec to p-adic factory

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

55c335e

Fixing doctest problems in the new change method for p-adic rings/fields

[sagetrac-git]

Changed commit from 53d2446 to 55c335e

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

fcc8aa5

Fixing various problems with the new change method

[sagetrac-git]

Changed commit from 55c335e to fcc8aa5

[sagetrac-git]

Changed commit from fcc8aa5 to 3b2d94a

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

3b2d94a

Remove old code for fraction_field and integer_ring from padic_extension_generic

[sagetrac-git]

Changed commit from 3b2d94a to f386dc6

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

f386dc6

Fix bug in ring_of_integers

[xcaruso]

comment:12

I'm a bit sceptical about the possibility of changing p (and even q). Can you show me a situation where this can be needed?

Adding show_prec is nice but is it really the subject of this ticket?

Doctests implying the keyword base are missing. The same is true for show_prec. More generally, I suggest to add many more doctests ensuring that your code works in a wide range of situations (for ramified, unramified extensions, for extensions constructing via CompletionFunction and AlgebraicExtensionFunctor, etc.)

[saraedum]

comment:13

Xavier: Thanks for having a look at this as well. We discussed the changing of p and q briefly and actually I find it very useful. Often I am only really interested in the ramified part of a tower of extensions (on my fork that already does more general towers.) But for some computation to work out, I need a certain unramified element at the bottom, so I don't want to manually reconstruct the whole tower, so raising and lowering q is quite useful. Changing p is mostly interesting in general extensions where you want to see how a certain polynomial behaves wrt to different primes. For the Eisenstein extensions that we support atm it is not too useful.

I think it's Ok to put the show_prec in here, I'm fine with reviewing it at least :)

I agree that doctests for base and show_prec should be added. However, I think that in general not all possible cases should be covered by explicit doctests. It usually makes the documentation overwhelming. If we want to have coverage, we should write unit tests for that instead. That's btw one of the topics that we want to push in Burlington! Imho, the testing for change is Ok except for the untested keywords.

[saraedum]

comment:14

David: should get_key_base set show_prec? Otherwise, show_prec=None and show_prec=True/False produces two non-identical parents for the same ring I think.

[saraedum]

Author: David Roe

[saraedum]

Reviewer: Julian Rüth

[saraedum]

Work Issues: show_prec in factory keys

[sagetrac-git]

Changed commit from 3142701 to 138d939

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

138d939

Fix string representation doctest from #22103

[roed314]

Diff against 23331

[roed314]

comment:56

Attachment: 20310_over_23331.diff.gz

For ease of reviewing, I've attached a diff against #23331.

[vbraun]

comment:57

PDF docs don't build

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

b18929a

Merge branch 'develop' into t/20310/change_precision

[sagetrac-git]

Changed commit from 138d939 to b18929a

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

86b58de

Fix latex error

[sagetrac-git]

Changed commit from b18929a to 86b58de

[roed314]

comment:60

Alright, make succeeds at building the docs now.

[saraedum]

comment:61

daucher still reports a failing docbuild. I guess that's because I told it not to clean the docs when rebuilding.

[vbraun]

Changed branch from u/roed/change_precision to 86b58de