# An extension of Berwald's inequality and its relation to Zhang's inequality

## TL;DR

This paper extends Berwald's inequality to a broader range of parameters for log-concave functions and applies it to give a new proof of Zhang's reverse Petty projection inequality, linking inequalities in convex analysis.

## Contribution

It generalizes Berwald's inequality for log-concave functions and uses this to provide a novel proof of Zhang's reverse Petty projection inequality.

## Key findings

- Extended the range of p for Berwald's inequality to (-1, ∞).
- Provided a new proof of Zhang's reverse Petty projection inequality.
- Demonstrated the connection between Berwald's inequality and Zhang's inequality.

## Abstract

In this note prove the following Berwald-type inequality, showing that for any integrable log-concave function $f:\mathbb R^n\rightarrow[0,\infty)$ and any concave function $h:L\rightarrow\mathbb [0,\infty)$, where $L$ is the epigraph of $-\log \frac{f}{\Vert f\Vert_\infty}$, then $$p\to \left(\frac{1}{\Gamma(1+p)\int_L e^{-t}dtdx}\int_L h^p(x,t)e^{-t}dtdx\right)^\frac{1}{p} $$ is decreasing in $p\in(-1,\infty)$, extending the range of $p$ where the monotonicity is known to hold true. As an application of this extension, we will provide a new proof of a functional form of Zhang's reverse Petty projection inequality, recently obtained in [ABG].