I am looking to characterize the maximum or minimum eigenvalues of a matrix $B = A Q A + \mathbf{I}-A$ where
- $A$ is positive semi-definite, symmetric, and has eigenvalues $\lambda_i\in[0,1)$
- $Q$ is positive definite and symmetric
- $\mathbf{I}$ is the identity matrix
It is apparent to me that this is positive definite because it is clearly symmetric and
- $x^\top B x = ||x||^2$ if $x\in Ker(A)$
- $x^\top B x \succeq x^\top A Q A x \succ 0$ if $x\notin Ker(A)$
I am wondering how can I find the maximum and minimum eigenvalues of B with respect to A and Q. If this is not possible, does there exist bounds that satisfy $l \mathbf{I}\preceq B \preceq u\mathbf{I}$ with $l>0$.
Appreciate any help or insight.