Dear all, I want to implement a modified Euler equation in 1D, using Version 4.2.0. For testing of a 1D case I set up a simple session file (attached, 20 equi-spaced elements, time and spatially independent initial and boundary conditions). The simulation does not run successfully. There seem to be several issues in the code which I was not able to solve up to now. So I try to describe what I have found so far and where I got stuck. 0) Is there a bug in my session file? 1) I noticed that Nektar::StdRegions::StdSegExp::v_ReduceOrderCoeffs is missing and implemented it. 2) When the Riemann Solver is called for the first time, an exception is thrown: Fatal : Level 0 assertion violation Where : /home/hkuehnelt/nektar/solvers/CompressibleFlowSolver/RiemannSolvers/ExactSolverToro.cpp[211] Message : Vacuum is generated by given data. By dumping a lot of stuff, I think I confined the problem, but have no clue where this comes from: In the call MultiRegions::DisContField1D::v_AddTraceIntegral(), called from SolverUtils::Advection::AdvectionWeakDG::v_Advect(), for the first convective field input Fn = {0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225,0.1225} and the output is {0.245,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}, i.e. the first value is non-zero. I assume, this is not correct. MultiRegions::DisContField1D::GetNegatedFluxNormal() returns the negatedFluxNormal = {0,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0} MultiRegions::DisContField1D::GetNegatedFluxNormal(): the problem seems to be in the first element of m_traceMap. Here the dump of IDs in the i and v loops. i v ID_elmtToTrace ID_leftAdjElem 0 0 0 0 0 1 0 0 1 0 1 0 1 1 1 1 2 0 2 1 2 1 2 2 3 0 3 2 3 1 3 3 ... 17 0 17 16 17 1 17 17 18 0 18 17 18 1 18 18 19 0 19 18 19 1 19 19 I tried to dig deeper, but then gave up, due to increasing complexity of the code. I am confident, that you help me. Best regards, Helmut