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A Point Counting Algorithm Using Cohomology with Compact Support

Published online by Cambridge University Press:  01 February 2010

Gweltaz Chatel
Affiliation:
IRMAR, Université de Rennes 1, France, gweltaz.chatel@laposte.net
David Lubicz
Affiliation:
IRMAR, Université de Rennes 1, France, david.lubicz@univ-rennes1.fr

Abstract

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We describe an algorithm to count the number of rational points of an hyperelliptic curve defined over a finite field of odd characteristic which is based upon the computation of the action of the Frobenius morphism on a basis of the Monsky-Washnitzer cohomology with compact support. This algorithm follows the vein of a systematic exploration of potential applications of cohomology theories to point counting.

Our algorithm decomposes in two steps. A first step which consists of the computation of a basis of the cohomology and then a second step to obtain a representation of the Frobenius morphism. We achieve a Õ(g4n3) time complexity and O(g3n3) memory complexity where g is the genus of the curve and n is the absolute degree of its base field. We give a detailed complexity analysis of the algorithm as well as a proof of correctness.

Information

Type
Research Article
Copyright
Copyright © London Mathematical Society 2009