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Computational Number Theory is for explicit calculations or algorithms involving anything of interest to number theorists.

2 votes
Accepted

on the computation of decomposition groups

Henri Cohen's A Course in Computational Algebraic Number Theory contains quite a bit of information. Chapters 4.8, 6.2 and 6.3 combined result in algorithms that compute decomposition groups. Note tha …
Dror Speiser's user avatar
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0 votes

Upper bound on greatest prime of bad reduction for a plane curve

The primes that are "bad" in your sense will divide the number $Res_x(Res_y(f,\frac{\partial f}{\partial x}), Res_y(f,\frac{\partial f}{\partial y}))$. (If I interpreted damiano's comment correctly). …
Dror Speiser's user avatar
  • 4,593
3 votes
2 answers
377 views

Upper bound on greatest prime of bad reduction for a plane curve

Background We are given a curve with integer coefficients. I want to make a suggestion in another question (Computationally bounding a curve's genus from below?) into a deterministic algorithm for fi …
Dror Speiser's user avatar
  • 4,593
11 votes
1 answer
562 views

CM field to Torus to Abelian Variety?

Given a CM field we can use its maximal order (and a choice of CM type) to construct an abelian variety $\mathbb{C}^g/\Lambda$ with complex multiplication by the maximal order. How do I (or where can …
Dror Speiser's user avatar
  • 4,593
7 votes
2 answers
727 views

Explicit map for Scholz reflection principle

The question is about the specific case of reflection theorems (copied straight from Franz Lemmermeyer's "Class Groups of Dihedral Extensions"): Let $k^+ = \mathbb{Q}(\sqrt{m})$ with $m\in \mathbb …
Dror Speiser's user avatar
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10 votes
3 answers
633 views

Computationally bounding a curve's genus from below?

Background In the course of answering another question (Infinite collection of elements of a number field with very similar annihilating polynomials) I found myself with a curve, that if it had a pos …
Dror Speiser's user avatar
  • 4,593
5 votes

What does the computer suggest about the parity of p(n), for n in a fixed arithmetic progres...

The answer to your very last question is yes. As for the rest: Computing the parity up to N is, in theory, quasi linear by using Pentagonal Number Theorem: compute the inverse of the pentagonal numbe …
Dror Speiser's user avatar
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2 votes
Accepted

Speeding the quadratic sieve with an oracle

If we know the factorization of $N$ then we can take square roots of small numbers that are quadratic residues mod all primes dividing $N$. Knowing a partial factorization of size $M\sim N^\alpha$, sq …
Dror Speiser's user avatar
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