Saturation estimates for hp-finite element methods

In this paper we will prove saturation estimates for the adaptive hp-finite element method for linear, second order partial differential equations. More specifically we will consider a sequence of nested finite element discretizations where we allow for both, local mesh refinement and locally increasing the polynomial order. We will prove that the energy norm of the error on the finer level can be estimated by the sum of a contraction of the old error and data oscillations. We will derive estimates of the contraction factor which are explicit with respect to the local mesh width and the local polynomial degree. In order to cover p-refinement of finite element spaces new polynomial projection operators will be introduced and new polynomial inverse estimates will be derived.