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Let $B \geq A \geq 0$ and $M \geq 0$ be real symmetric matrices. Is it true that

$B M B \geq A M A$, i.e., $B M B - A M A \geq 0$?

I. Amon
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1 Answers1

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No. It is known, for instance, that $B\ge A\ge0$ does not imply $B^2\ge A^2$. Now pick such a pair of matrices $A$ and $B$ and set $M=I$.

user1551
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