Do not try to create embedded number field morphisms for non-embedded number fields

[simon-king-jena]

The attempt to create an embedded number field morphisms for non-embedded number fields currently fails (and should of course fail).

sage: L.<i> = NumberField(x^2 + 1)
sage: K = NumberField(L(i/2+3).minpoly(), names=('i0',), embedding=L(i/2+3))
sage: from sage.rings.number_field import number_field_morphisms
sage: number_field_morphisms.EmbeddedNumberFieldMorphism(R, self)
Traceback (most recent call last):
...
RuntimeError: maximum recursion depth exceeded in __instancecheck__

However, instead of running into an infinite recursion, a quick and simple ValueError (or perhaps TypeError) should be raised.

CC: @jpflori

Component: number fields

Author: Simon King, Marc Mezzarobba, Jean-Pierre Flori

Branch/Commit: 2bedaa1

Reviewer: Marc Mezzarobba, Jean-Pierre Flori

Issue created by migration from https://trac.sagemath.org/ticket/15331

[simon-king-jena]

Branch: u/SimonKing/ticket/15331

[simon-king-jena]

New commits:

[changeset:2123372]

Raise type error for number field morphisms of non-embedded number fields

[simon-king-jena]

Commit: 2123372

[simon-king-jena]

Author: Simon King

[mezzarobba]

comment:3

Hi Simon,

I'm trying to review this ticket, but there are a couple of things I don't understand:

• why can't EmbeddedNumberFieldMorphism try using the algebraic closure by itself?

• even if it really can't, is the giant except clause on line 6194 of number_field.py necessary?

• shouldn't

              Lemb = Lemb.codomain() # number_field_morphisms.pyx:187
              while Lemb.coerce_embedding() is not None:
                  Lemb = Lemb.coerce_embedding().codomain()
                  ambient_field = pushout(Kemb, Lemb)

  read

              Lemb = Lemb.codomain()
              while Lemb.coerce_embedding() is not None:
                  Lemb = Lemb.coerce_embedding().codomain()
              ambient_field = pushout(Kemb, Lemb)

  ?

Sorry if these are stupid questions, I'm still trying to learn how this all works!

My attempt at simplifying the code based on these remarks is at u/mmezzarobba/embedded_NF_morphisms.

[jpflori]

comment:6

Replying to @mezzarobba:

Hi Simon,

I'm trying to review this ticket, but there are a couple of things I don't understand:

• why can't EmbeddedNumberFieldMorphism try using the algebraic closure by itself?

• even if it really can't, is the giant except clause on line 6194 of number_field.py necessary?

• shouldn't

              Lemb = Lemb.codomain() # number_field_morphisms.pyx:187
              while Lemb.coerce_embedding() is not None:
                  Lemb = Lemb.coerce_embedding().codomain()
                  ambient_field = pushout(Kemb, Lemb)

  read

              Lemb = Lemb.codomain()
              while Lemb.coerce_embedding() is not None:
                  Lemb = Lemb.coerce_embedding().codomain()
              ambient_field = pushout(Kemb, Lemb)

  ?

Sorry if these are stupid questions, I'm still trying to learn how this all works!

My attempt at simplifying the code based on these remarks is at u/mmezzarobba/embedded_NF_morphisms.

Any remark on this Simon?

If you're too busy, I'll just have a look for myself and try to take some action to get this merged.