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Time table of all LIRMM seminars

All LIRMM seminars, sorted by team or theme

July 2025

Mon Tue Wed Thu Fri Sat Sun
Tuesday 1 July
  • 15 h 00 min – 16 h 00 min Evgeny Gurevsky, «Day-ahead lot-sizing under uncertainty: An application to green hydrogen production»
    15 h 00 min – 16 h 00 min
    Evgeny Gurevsky, «Day-ahead lot-sizing under uncertainty: An application to green hydrogen production»
    E3.24

    We investigate the short-term production planning of green hydrogen obtained by water electrolysis using electricity from a wind power source and a connection to the national electricity grid. Electricity consumption on the grid has to be declared a day before production and cannot be adjusted afterwards, while the future availability of the wind power source is uncertain. This production problem can be viewed as a two-stage stochastic lot-sizing model, and a consistent framework is introduced to solve it efficiently. First, the innovative use of a variational auto-encoder to estimate the conditional uncertainty of wind power and generate scenarios is studied. Next, a time-efficient Benders decomposition approach is proposed, in which the special features of our problem are exploited to speed up its solving. Finally, a new application of an adaptive partition-based approach and a stabilization method further improve the solution time of the decomposition scheme. A realistic simulation demonstrates the advantages of the framework presented.

    (Joint work with Céline Gicquel and Victor Spitzer)

Wednesday 2 July
Thursday 3 July
  • 10 h 00 min – 11 h 00 min Dimitrios Thilikos, «Structural Theorems for Colorful Minors and Algorithmic Applications»
    10 h 00 min – 11 h 00 min
    Dimitrios Thilikos, «Structural Theorems for Colorful Minors and Algorithmic Applications»
    E.3.23

    A $q$-colorful graph $(G, f)$ is a graph $G$ together with a vertex-coloring function $f: V(G) \to \{1, \ldots, q\}$. Such graphs naturally capture a wide range of algorithmic problems on graphs involving distinguished sets of terminals. The concept of graph minors extends in a natural way to colorful graphs. However, to understand the complexity landscape of related problems, especially in the presence of terminals, a structural theory of colorful minors is essential. In this talk, we present three structural theorems concerning the exclusion of specific colorful graphs as minors. These are:

    1. the rainbow clique — a clique in which each vertex is assigned all colors,

    2. the rainbow grid — a grid in which every vertex carries all colors, and

    3. segregated grids — all grids with all colors appearing segregated and in sequence on the outer face.

    Our results yield a complete answer to the question of when the Erdős–Pósa property holds for colorful minors, for any possible number of colors. Beyond this, they lead to new meta-algorithmic results for graph problems with terminal constraints—problems that fall outside the reach of existing algorithmic frameworks.

    Joint work with Evangelos Protopapas and Sebastian Wiederrecht

Friday 4 July
Saturday 5 July
Sunday 6 July
Monday 7 July
Tuesday 8 July
Wednesday 9 July
Thursday 10 July
Friday 11 July
Saturday 12 July
Sunday 13 July
Monday 14 July
Tuesday 15 July
Wednesday 16 July
Thursday 17 July
Friday 18 July
Saturday 19 July
Sunday 20 July
Monday 21 July
Tuesday 22 July
  • 11 h 00 min Michaël Poss, «Iterated local search algorithms for discrete adjustable robust optimization problems»
    11 h 00 min – 11 h 00 min
    Michaël Poss, «Iterated local search algorithms for discrete adjustable robust optimization problems»
    E3.24

    Two-stage robust optimization with integer recourse is a notoriously difficult class of problems, yet modelling many important applications. In this we talk, we discuss how to heuristically solve these problems, solving the adversarial problem and the outer minimization problem through local search algorithms. We focus on the case where all decision variables as well as the uncertainty are discrete sets. We compare numerically our algorithms with the recent exact algorithm recently proposed in the literature.

Wednesday 23 July
Thursday 24 July
Friday 25 July
Saturday 26 July
Sunday 27 July
Monday 28 July
Tuesday 29 July
Wednesday 30 July
Thursday 31 July