grandes-ecoles 2023 Q5

grandes-ecoles · France · mines-ponts-maths1__pc Proof by induction Prove a general algebraic or analytic statement by induction
Let $M \in S_n^+(\mathbf{R})$ be a non-zero matrix. Show the inequality $\frac{\operatorname{Tr}(M)}{n} \geq \operatorname{det}^{1/n}(M)$.
Hint: You may show that $x \mapsto -\ln(x)$ is convex on $\mathbf{R}_+^\star$.
Let $M \in S_n^+(\mathbf{R})$ be a non-zero matrix. Show the inequality $\frac{\operatorname{Tr}(M)}{n} \geq \operatorname{det}^{1/n}(M)$.

Hint: You may show that $x \mapsto -\ln(x)$ is convex on $\mathbf{R}_+^\star$.