The power method for the generalized eigenvalue problem

In this paper the Power Method for the generalized eigenvalue problem for matrix pencil (A-B)x=0 is considered. At any step of this iterative process the system of linear algebraic equations By-Ax has to be approximately solved with respect to y. We try to answer the question: how accurately we have to solve this system on each step of iteration,in order to guarantee resolution of the eigenproblem with given precision.