Opened 4 years ago

Last modified 4 years ago

#22494 needs_work enhancement

ramification properties of quaternion algebras

Reported by: aurel Owned by:
Priority: major Milestone: sage-7.6
Component: number theory Keywords: days84, quaternion algebras, hilbert symbol, ramification
Cc: aly.deines, tornaria, mmasdeu Merged in:
Authors: Aurel Page Reviewers:
Report Upstream: N/A Work issues:
Branch: u/aurel/quatalg_ramification (Commits) Commit: a828d9e5eb56934f185d9b49b29edb40105f1958
Dependencies: Stopgaps:

Description

Improvements:

  • no duplicate factorisations (ramified_primes)
  • doc correctly states that ramified_primes is implemented over number fields
  • add ramified_infinite_places
  • is_division_algebra over number fields
  • is_matrix_ring over number fields

Change History (6)

comment:1 Changed 4 years ago by aurel

  • Branch set to u/aurel/quatalg_ramification

comment:2 Changed 4 years ago by aurel

  • Cc aly.deines tornaria mmasdeu added
  • Commit set to a828d9e5eb56934f185d9b49b29edb40105f1958
  • Status changed from new to needs_review

New commits:

ecc7ac8add hilbert_ramification
1c421f8quatalg ramification: discriminant over nf and factor only once
0fd6575quatalg: add ramified_infinite_places
a828d9equatalg: is_division_algebra and is_matrix_ring over nf

comment:3 Changed 4 years ago by aurel

I am not sure about the list vs set choice in ramified_primes and ramified_infinite_places. Tell me what I should do!

Last edited 4 years ago by aurel (previous) (diff)

comment:4 Changed 4 years ago by aurel

  • Keywords days84 added

comment:5 Changed 4 years ago by vdelecroix

  • Status changed from needs_review to needs_work

Hello,

some quick comments regarding code clarity.

Why in the function ramified_primes(self) do you need

raise ValueError("base field must be rational numbers or number field")

From what I understand it is not possible to construct a quaternion algebra over something else than a number field.

Are you sure one needs hilbert_ramification in the global namespace (modif. in sage.arith.all)? I would be in favor of removing all of hilbert_symbol, hilbert_conductor, hilbert_conductor_inverse from the global namespace.

ram = set()
for p in set().union([ZZ(2)], prime_divisors(a), prime_divisors(b)):
    if hilbert_symbol(a, b, p) == -1:
        ram.add(p)
return ram

could be

return set(p for p in set().union([ZZ(2)], prime_divisors(a), prime_divisors(b)) if hilbert_symbol(a, b, p) == -1)

(up to you, not sure it is more readable)

Keep spaces around ==. len(ram)==0 should be len(ram) == 0.

Why do you use once set.union and the other time union?

comment:6 Changed 4 years ago by aurel

Hello,

Thanks for your review.

It is possible to construct a quaternion algebra over something else than a number field: try

sage: K.<x> = FunctionField(QQ)
sage: A = QuaternionAlgebra(K,-1,x)
sage: A.ramified_primes()

But constructing it from its ramification only makes sense over certain fields, including number fields.

I am ok with removing hilbert_* from the global namespace, but that breaks backwards compatibility: several of these function were defined before my patch. Should they be methods of QQ or something else?

I will take into account your code suggestions.

The set.union vs union is because I simply moved around the existing code for the two versions of hilbert_conductor. I can uniformise it.

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