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**Counting rational points on curves and abelian varieties over finite fields.**
*(English)*
Zbl 0898.11045

Cohen, Henri (ed.), Algorithmic number theory. Second international symposium, ANTS-II, Talence, France, May 18-23, 1996. Proceedings. Berlin: Springer. Lect. Notes Comput. Sci. 1122, 1-16 (1996).

Let \(A\) be an abelian variety of dimension \(g\) over a finite field \({\mathbb F}_q\). Suppose that \(A\) is given as a closed subvariety of projective \(n\)-space. The authors exhibit a deterministic algorithm that computes the characteristic polynomial of the Frobenius endomorphism of \(A\) that runs in time \(O((\text{log} q)^c)\), where \(c\) is a polynomial expression in \(g\) as well as \(n\). This improves upon an earlier result of J. Pila [Math. Comput. 55, 745-763 (1990; Zbl 0724.11070)], who obtained a similar result but with the constant \(c\) depending exponentially on \(n\).

By applying this to the Jacobian varieties of curves \(X\) over \({\mathbb F}_q\), one obtains a deterministic algorithm to count the number of \({\mathbb F}_q\)-rational points of \(X\) that runs in time \(O((\text{log} q)^c)\), where \(c\) is a polynomial expression in \(n\), as well as the genus \(g\) of \(X\). In the special case of hyperelliptic curves of genus \(g\), the authors show that the number of \({\mathbb F}_q\)-rational points on \(X\) can be counted deterministically in time \((\text{log} q)^{O(g^6)}\). This case is of interest in view of the primality test decribed by the authors in their monograph [Primality testing and abelian varieties over finite fields, Lect. Notes Math. 1512 (Springer-Verlag, 1992; Zbl 0744.11065)].

For the entire collection see [Zbl 0852.00023].

By applying this to the Jacobian varieties of curves \(X\) over \({\mathbb F}_q\), one obtains a deterministic algorithm to count the number of \({\mathbb F}_q\)-rational points of \(X\) that runs in time \(O((\text{log} q)^c)\), where \(c\) is a polynomial expression in \(n\), as well as the genus \(g\) of \(X\). In the special case of hyperelliptic curves of genus \(g\), the authors show that the number of \({\mathbb F}_q\)-rational points on \(X\) can be counted deterministically in time \((\text{log} q)^{O(g^6)}\). This case is of interest in view of the primality test decribed by the authors in their monograph [Primality testing and abelian varieties over finite fields, Lect. Notes Math. 1512 (Springer-Verlag, 1992; Zbl 0744.11065)].

For the entire collection see [Zbl 0852.00023].

Reviewer: RenĂ© Schoof (Amsterdam)

### MSC:

11Y16 | Number-theoretic algorithms; complexity |

11G25 | Varieties over finite and local fields |

11G20 | Curves over finite and local fields |

14K15 | Arithmetic ground fields for abelian varieties |

14G05 | Rational points |

14G15 | Finite ground fields in algebraic geometry |

14Q05 | Computational aspects of algebraic curves |

14Q15 | Computational aspects of higher-dimensional varieties |

14H25 | Arithmetic ground fields for curves |