I have the following quadratic matrix equation: $$ XAX+X = B $$ where both $A$ and $B$ are given positive definite matrices, and $X$ is a covariance matrix and, hence, positive definite. When there is no constraint, the equation can be solved via Bernoulli iteration in the following form: $$X_{k+1} = -A^{-1}(I-BX_k^{-1})$$ However, this does not seems to preserve positive semidefinite. Any guidance would be appreciated. Thank you.