Search Results for author: Walid Hachem

Found 6 papers, 0 papers with code

Equilibria of large random Lotka-Volterra systems with vanishing species: a mathematical approach

no code implementations15 Feb 2023 Imane Akjouj, Walid Hachem, Mylène Maïda, Jamal Najim

Ecosystems with a large number of species are often modelled as Lotka-Volterra dynamical systems built around a large random interaction matrix.

Complex systems in Ecology: a guided tour with large Lotka-Volterra models and random matrices

no code implementations12 Dec 2022 Imane Akjouj, Matthieu Barbier, Maxime Clenet, Walid Hachem, Mylène Maïda, François Massol, Jamal Najim, Viet Chi Tran

Ecosystems represent archetypal complex dynamical systems, often modelled by coupled differential equations of the form $$ \frac{d x_i}{d t} = x_i \varphi_i(x_1,\cdots, x_N)\ , $$ where $N$ represents the number of species and $x_i$, the abundance of species $i$.

Stochastic Subgradient Descent Escapes Active Strict Saddles on Weakly Convex Functions

no code implementations4 Aug 2021 Pascal Bianchi, Walid Hachem, Sholom Schechtman

Consequently, generically in the class of definable weakly convex functions, the SGD converges to a local minimizer.

Stochastic Optimization

A Fully Stochastic Primal-Dual Algorithm

no code implementations23 Jan 2019 Pascal Bianchi, Walid Hachem, Adil Salim

The proposed algorithm is proven to converge to a saddle point of the Lagrangian function.

A Constant Step Stochastic Douglas-Rachford Algorithm with Application to Non Separable Regularizations

no code implementations3 Apr 2018 Adil Salim, Pascal Bianchi, Walid Hachem

The Douglas Rachford algorithm is an algorithm that converges to a minimizer of a sum of two convex functions.

Snake: a Stochastic Proximal Gradient Algorithm for Regularized Problems over Large Graphs

no code implementations19 Dec 2017 Adil Salim, Pascal Bianchi, Walid Hachem

When applying the proximal gradient algorithm to solve this problem, there exist quite affordable methods to implement the proximity operator (backward step) in the special case where the graph is a simple path without loops.

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