I am wondering if $Q, P$ are similar matrices where for a function
$f:\mathbb{R^n}\to\mathbb{R}$ and for a diagonal matrix $D$
$Q=I-D^{-1}\nabla^2f(x)$ and $P=I-D^{-1/2}\nabla^2f(x)D^{-1/2}$.
Similar matrix definition: $A,B$ are similar if $A=P^{-1}BP$ for some $P$.