Hi Jian, Sorry for the slow response, this is grading time in the UK. This might be due to the preconditioners not being very smart in 2D. I think there might be a BlockDiagonal preconditioned in 2D which could possibly work much better. In 3D we have a number of preconditioners set up. I probably need to have a look at this but may not get a chance until you are over in a couple of weeks. Cheers, Spencer. On 25 May 2016, at 02:04, Jian Yu <yuj@buaa.edu.cn<mailto:yuj@buaa.edu.cn>> wrote: Dear all, I encountered a problem when I run the FieldConvert with two or more cpu cores for the C0Projection module. For example, when I run the following command, it is OK: mpirun -np 1 ./FieldConvert -m C0Projection 2D_20x20.xml 2D_20x20_0.chk 2D_20x20_0_C0.fld However, the following command will report an error: mpirun -np 2 ./FieldConvert -m C0Projection 2D_20x20.xml 2D_20x20_0.chk 2D_20x20_0_C0.fld and the error message is: gs_setup: 60 unique labels shared pairwise times (avg, min, max): 0.000110245 0.00010879 0.000111699 crystal router : 9.22918e-05 9.22918e-05 9.22918e-05 all reduce : 0.000179148 0.0001791 0.000179195 used all_to_all method: crystal router handle bytes (avg, min, max): 4724 4724 4724 buffer bytes (avg, min, max): 1920 1920 1920 CG iterations made = 5001 using tolerance of 1e-09 (error = nan, rhs_mag = inf) Fatal : Level 0 assertion violation Exceeded maximum number of iterations terminate called after throwing an instance of 'ErrorUtil::NekError' what(): Level 0 assertion violation Exceeded maximum number of iterations Can anyone help me about this? Best Jian _______________________________________________ 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