Abstract

A CM-order is a reduced order equipped with an involution that mimics complex conjugation. The Witt--Picard group of such an order is a certain group of ideal classes that is closely related to the...

Highlights

  • An order is a commutative ring of which the additive group is isomorphic toZn for some n ∈ Z≄0

  • In algorithms one specifies an automorphism of an order by means of its matrix on the same Z-basis α1, . . . , αn that was used for the bijk

  • An A-lattice L is invertible if the values of the map φL of Proposition 4.1 all lie in A and the map φL : L ⊗A L → A is an isomorphism of A-modules

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Summary

Introduction

The group of roots of unity in A might be too large to even write down in polynomial time, so the set of short vectors in L and the set of all A-isomorphisms from L to A might be too large to enumerate Our work on this subject was inspired by an algorithm of Gentry and Szydlo (Section 7 of [4]), and is related to our work on lattices with symmetry [11, 12].

CM-fields and CM-algebras
CM-orders
A-lattices
Reduced bases
Short vectors in lattice cosets
Short vectors and regular elements
Vigilant sets and lower bounds
Ideal lattices
10. Invertible A-lattices
11. Short vectors in invertible lattices
12. The Witt-Picard group
13. Multiplying and exponentiating invertible A-lattices
14. The extended tensor algebra Λ
15. Some elementary number theory
16. Finding auxiliary ideals
17. Using the auxiliary ideals
18. Main algorithm
Full Text
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