Hi all,<br><br>With p number of processors in the communicator, the block preconditioner PC_BJACOBI will by default use p blocks. So far, so good. However, in order to compare this algorithmic efficiency decrease (since the bigger p, the less efficient the preconditioner), i ran the commands<br>
<br><span style="font-family: courier new,monospace;">mpirun -n 1 ./program -pc_bjacobi_blocks 8 </span><br><span style="font-family: courier new,monospace;">mpirun -n 8 ./program -pc_bjacobi_blocks 8 </span><br><br>I expected the preconditioning to be equally efficient in this case. However, GMRES makes more iterations in the first case (30 against 28) which I cannot explain. Are there more subtle differences about the preconditioner or the KSP that i'm overlooking here?<br>
<br>regards,<br><br>Leo<br><br><br><br><br><br>