Good Morning,

I usually solve a non-symmetric discretization of the Poisson equation using GAMG+FGMRES.

In the last days I tried to use BCGS in place of FGMRES, still using GAMG as preconditioner.
No problem in finding the solution but I’m experiencing something I didn’t expect.

The test case is a 25 millions cells domain with Dirichlet and Neumann boundary conditions.
Both the solvers are able to solve the problem with an increasing number of MPI processes, but:

• FGMRES is about 25% faster than BCGS for all the processes number
• Both solvers have the same scalability from 48 to 384 processes
• Both solvers almost use the same amount of memory (FGMRES use a restart=30)

Am I wrong expecting less memory consumption and more performance from BCGS with respect to FGMRES?

Thank you in advance for any help.

Best regards,

Marco Cisternino