On the Generalization of Weinberger's Inequality with Alternating Signs

Abstract

For given set of $m$ positive numbers satisfying the conditions: $$ a_1 \geq a_2 \geq , ... \geq a_m \geq 0, $$ the inequality $$ \sum_{s=1}^{m} (-1)^{s-1}a^r_s \geq \left[ \sum_{s=1}^{m} (-1)^{s-1}a_s\right]^r, \quad r > 1, $$ was proved by H. Weinberger. The generalization of Weinberger's result takes the form $$ \sum_{s=1}^{m} (-1)^{s-1}f(a_s) \geq f\left( \sum_{s=1}^{m} (-1)^{s-1}a_s\right), $$ where $f$ is a convex function satisfying the condition $f(0)\leq 0 $. The condition $f(0)\geq 0 $ in the generalization proposed by Bellman was corrected by Olkin as $f(0) \leq 0 $. Bellman gave only a graphical proof for differentiable convex functions. In this paper, we give a mathematical proof for the generalized inequality including the importance of the condition $f(0)\leq 0$. We introduce a set $\mathcal{W}$ of functions so that functions in the intersection of $\mathcal{W}$ and the set of all convex functions are the ones that are desirable in the generalization. In addition, we give a proof of Szeg\"{o}'s inequality which applies to sums with odd number of terms.