A Poincar\'e type inequality with three constraints

TL;DR

This paper investigates a calculus of variations problem related to a Poincaré inequality with three constraints, aiming to find the minimal value of a specific functional involving periodic functions with orthogonality conditions.

Contribution

It provides the computation of the minimum of a variational problem connected to a quantitative isoperimetric inequality in the plane, considering three orthogonality constraints.

Findings

Derived the explicit minimum of the variational problem.

Connected the problem to a Poincaré-type inequality with constraints.

Enhanced understanding of inequalities in the calculus of variations.

Abstract

In this paper, we consider a problem in calculus of variations motivated by a quantitative isoperimetric inequality in the plane. More precisely, the aim of this article is the computation of the minimum of the variational problem $$\inf_{u\in\mathcal{W}}\frac{\displaystyle\int_{-\pi}^{\pi}[(u')^2-u^2]d\theta}{\displaystyle\left[\int_{-\pi}^{\pi}|u| d\theta\right]^2}$$where $u\in \mathcal{W}$ is a $H^1(-\pi,\pi)$ periodic function, with zero average on $(-\pi,\pi)$ and orthogonal to sine and cosine.