Hi Stan, Thanks for your feedback. The channel flow stability test (Tests/ChanStability.xml) uses a base flow (.bse) and an initial guess (.rst) and converges to an expected result. Now, as practice I tried to play around with the settings, first by changing the Driver to Arpack (this works as well). Since I might not know the initial approximation I tried to get rid of the initial guess, and replaceed it with some random initial vector (I have put zeros, non zeros, the awgn()). This time the problem did not coverage at all (I increased the numbers of iterations, tried to modify the number and size of the time steps, change the dimension of the Krylov space). Is this an expected behaviour? And since this is a test, the problem is set up to be small and quick and would only converge with the proper initial vector? Should I expect a similar problem for a larger 3D case? It should converge. Quite possibly having zero initial conditions might cause problems but having non-zero or awgn() should have worked. It can take quite a few iterations since the channel problem has a very small growth rate. As you note we have a simplified regression test to make sure it does not take too long to run. Can I ask if you were using the 2.5D instability ( a Fourier mode in the span wise direction) or the 2D instability. We did have an issue with the 2.5D code which has recently been fixed and I think is part of the current Master on the repository (Chris can you confirm if this is true). Can I first check you are using the most recent version of Master? My second question concerns the base flow. I tried to recover the base flow using the stationary solver (both classical and adaptive) but I failed. Could you point me at an example of how to set this up? Also I noticed (or I think I did) that the Example/ChanStability-Base.xml does not produce a correct flow field. Am I right? Again can we find out which stationary solver you were running. Was this using the Selective frequency damping? If so perhaps Bastien can help check what might be going on here. Alternatively we tend to run base flows using the time marching methods until they get to a steady state. I have just run the ChanStability-Base.xml case and get an error of L 2 error (variable u) : 0.00187368 L inf error (variable u) : 0.000533519 L 2 error (variable v) : 1.21301e-11 L inf error (variable v) : 6.97233e-10 L 2 error (variable p) : 6.41086e-10 L inf error (variable p) : 2.31381e-10 which does not seem correct. Is this also the answer you observe (note I only ran it for 2000 steps). Cheers, Spencer. I would appreciate if you would comment on my questions. Best Regards, Stan Gepner _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk<mailto:Nektar-users@imperial.ac.uk> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users Spencer Sherwin McLaren Racing/Royal Academy of Engineering Research Chair, Professor of Computational Fluid Mechanics, Department of Aeronautics, Imperial College London South Kensington Campus London SW7 2AZ s.sherwin@imperial.ac.uk<mailto:s.sherwin@imperial.ac.uk> +44 (0) 20 759 45052