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Zakaria Fattah

Publications and source records attributed to Zakaria Fattah.

4 recordsLinked to original sources

Blaschke--Santal{ó} diagram for the volume, the diameter, and the Cheeger constant

We study the Blaschke--Santal{ó} diagram associated with the volume, the diameter, and the Cheeger constant. In the class of bounded open subsets of $\mathbb{R}^m$, $m\ge 2$, we give a complete description of the diagram. In the class of convex bodies of $\mathbb R^m$, we prove that the diagram is closed and simply connected as it is given by the region between two continuous functions for which qualitative properties such as monotonicity, local behavior, and growth estimates are studied.

math.OC

Optimal $L^p$-approximation of convex sets by convex subsets

Given a convex set $Ω$ of $\mathbb{R}^n$, we consider the shape optimization problem of finding a convex subset $ω\subset Ω$, of a given measure, minimizing the $p$-distance functional $$\mathcal{J}_p(ω) := \left(\int_{\mathbb{S}^{n-1}} |h_Ω-h_ω|^p d\mathcal{H}^{n-1}\right)^{\frac{1}{p}},$$ where $1 \le p <\infty$ and $h_ω$ and $h_Ω$ are the support functions of $ω$ and the fixed container $Ω$, respectively. We prove the existence of solutions and show that this minimization problem $Γ$-converges, when $p$ tends to $+\infty$, towards the problem of finding a convex subset $ω\subset Ω$, of a given measure, minimizing the Hausdorff distance to the convex $Ω$. In the planar case, we show that the free parts of the boundary of the optimal shapes, i.e., those that are in the interior of $Ω$, are given by polygonal lines. Still in the $2-d$ setting, from a computational perspective, the classical method based on optimizing Fourier coefficients of support functions is not efficient, as it is unable to efficiently capture the presence of segments on the boundary of optimal shapes. We subsequently propose a method combining Fourier analysis and a recent numerical scheme, allowing to obtain accurate results, as demonstrated through numerical experiments.

math.OC

A reverse isoperimetric inequality for planar ($α$, $β$)--convex bodies

In this paper, we study a reverse isoperimetric inequality for planar convex bodies whose radius of curvature is between two positive numbers 0 < $α$ < $β$, called ($α$, $β$)--convex bodies. We show that among planar ($α$, $β$)--convex bodies of fixed perimeter, the extremal shape is a domain whose boundary is composed by two arcs of circles of radius $α$ joined by two arcs of circles of radius $β$.

math.OC