Dispersive and dissipative errors in the DPG method with scaled norms for Helmholtz equation

We consider the discontinuous Petrov-Galerkin (DPG) method, wher the test space is normed by a modified graph norm. The modificatio scales one of the terms in the graph norm by an arbitrary positive scaling parameter. Studying the application of the method to the Helmholtz equation, we find that better results are obtained, under some circumstances, as the scaling parameter approaches a limiting value. We perform a dispersion analysis on the multiple interacting stencils that form the DPG method. The analysis shows that the discrete wavenumbers of the method are complex, explaining the numerically observed artificial dissipation in the computed wave approximations. Since the DPG method is a nonstandard least-squares Galerkin method, we compare its performance with a standard least-squares method.