I am solving the linear elasticity equation within a FEM library with a complex 3D geometry. The resulting linear system is solved with CG, preconditioned by AMG (Algebraic Multigrid). The computed numerical solution is correct. However, when running the program with different numbers of processors, say going from 5 to 10 MPI ranks, the of iterations count slightly changes from 300 to 303.
The solution looks identical of course, but I am quite puzzled by this fact. Is this something that can happen with AMG when running in parallel? I am using TrilinosML, so the AMG implementation is kind of a black box to me right now.