I know that it is possible to determine the theoretical order of accuracy (B) of numerical solutions in FVM (for instance for a steady problem in which only the central differencing scheme (CDS) is used to interpolate, B = 2 since CDS is 2nd order accurate). I know that with FVM the order of accuracy is obtained from the Taylor series.
I interested to know whether there is a method to obtain the convergence rate for FEM solutions.
I am also particularly interested to find out if there is a way of determining the order of accuracy for DGFEM. I have read in many papers that the convergence rate is normally p+1 where p is degree of the approximating polynomial. However I am uncertain as why this is not effected by the interpolation scheme used for the flux terms.