#### Venue

Sala Seminari (Dip. Matematica).

#### Abstract

We focus our attention on shape optimization problems in which one dimensional connected objects are involved. Very old and classical problems in calculus of variation are of this kind: euclidean Steiner’s tree problem, optimal irrigation networks, cracks propagation, etc. In a first part we quickly recall some previous work in collaboration with F. Santambrogio related to the functional relaxation of the irrigation cost. We establish a $\Gamma$-convergence of Modica and Mortola’s type and illustrate its efficiency from a numerical point of view by computing optimal networks associated to simple sources/sinks configurations. We also present more evolved situations with non Dirac sinks in which a fractal behavior of the optimal network is expected. In the second part of the talk we restrict our study to the euclidean Steiner’s tree problem. We recall recent numerical approach which have been developed the last five years to approximate optimal trees: partitioning formulation, relaxation with geodesic distance terms and energetic constraints. We describe the first results obtained in collaboration with A. Massaccesi and B. Velichkov to certify the optimality of a given tree. With our discrete parametrization of generalized calibration, we are able to recover the theoretical optimal matrix fields which certify the optimality of simple trees associated to the vertices of regular polygons. Finally, we focus on the delicate problem of the identification of the optimal structure. Based on a recent approach obtained in collaboration with G. Orlandi and M. Bonafini, we describe the first convexification framework associated to the Euclidean Steiner tree problem which provide relevant tools from a numerical point of view.