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