HI Hongtao, You can compile Nektar++ without the NEKTAR_USE_MPI flag, or go into ccmake from your builds directory and toggle off NEKTAR_USE_MPI, reconfigure and this should then generate a configuration wtihouth mpi. Alternatively you can try running “ModifiedArnoldi” instead of Arpack. I think that does run in parallel. Cheers, Spencer. From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of 🌸那慢慢🌸 <2644878715@qq.com> Date: Friday, 10 May 2024 at 12:37 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] ARPACK is not set-up for parallel execution This email from 2644878715@qq.com originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list<https://spam.ic.ac.uk/SpamConsole/Senders.aspx> to disable email stamping for this address. Dear nektar++ users and developers, I get the error "ARPACK is not set-up for parallel execution" when running the incompressbile flow solver in parallel with MPI，but in the file build/CMakeCache.tst have a line saying:NEKTAR_USE_MPI:BOOL=ON.How do I fix this? Hongtao Cheng