# Current

Unless stated otherwise, the seminar takes place on Tuesdays, from 10 to 11, in room 385 at IMB. To get announcements, you can subscribe to the mailing-list.- 2021-02-0210:00OnlineBogdan Dina (Ulm University)Isogenous hyperelliptic and non-hyperelliptic jacobians with maximal complex multiplication
We analyze complex multiplication for Jacobians of curves of genus 3, as well as the resulting Shimura class groups and their subgroups corresponding to Galois conjugation over the reflex field. We combine our results with numerical methods to find CM fields $K$ for which there exist both hyperelliptic and non-hyperelliptic curves whose Jacobian has complex multiplication by $\mathbb{Z}_K$.

- 2021-03-1610:00OnlineVincent Neiger (Université de Limoges)Deterministic computation of the characteristic polynomial in the time of matrix multiplication
This talk describes joint work with Clément Pernet on an algorithm which computes the characteristic polynomial of a matrix over a field within the same asymptotic complexity, up to constant factors, as the multiplication of two square matrices. Previously, this was only achieved by resorting to genericity assumptions or randomization techniques, while the best known complexity bound with a general deterministic algorithm was obtained by Keller-Gehrig in 1985 and involves logarithmic factors. The new algorithm computes more generally the determinant of a univariate polynomial matrix in reduced form.