Hi Barry, Can you point me the documentation for understanding these iteration patterns? Thanks a lot.
Best, Xiangdong On Fri, Sep 29, 2017 at 11:24 AM, Barry Smith <bsm...@mcs.anl.gov> wrote: > > They are all different iteration patterns. They definitely should > present different residual results > > > > On Sep 29, 2017, at 8:19 AM, Xiangdong <epsco...@gmail.com> wrote: > > > > Hello everyone, > > > > I have a questions about residuals reported in pc_composite. For the > examples in petsc-3.7.6/src/ksp/ksp/examples/tutorials/ex1.c, I found > that when I use these three options: > > > > 1) -pc_type none > > 2) -pc_type composite -pc_composite_pcs none,none -pc_composite_type > multiplicative > > 3) -pc_type composite -pc_composite_pcs none,none -pc_composite_type > multiplicative -ksp_norm_type unpreconditioned > > > > as shown below, it reported different KSP residuals. Given that I use > the identity preconditioner (with multiplicative), why does the residual > vary for different options? > > > > Thanks. > > > > Best, > > Xiangdong > > > > mpirun -np 1 ./extest -ksp_monitor -pc_type none > > > > 0 KSP Residual norm 1.414213562373e+00 > > 1 KSP Residual norm 6.324555320337e-01 > > 2 KSP Residual norm 3.779644730092e-01 > > 3 KSP Residual norm 2.581988897472e-01 > > 4 KSP Residual norm 1.906925178491e-01 > > 5 KSP Residual norm 1.616509124176e-15 > > > > mpirun -np 1 ./extest -ksp_monitor -pc_type composite -pc_composite_pcs > none,none -pc_composite_type multiplicative > > > > 0 KSP Residual norm 1.414213562373e+00 > > 1 KSP Residual norm 1.176696810829e+00 > > 2 KSP Residual norm 1.096908636191e+00 > > 3 KSP Residual norm 4.389821446437e-01 > > 4 KSP Residual norm 2.088364906576e-01 > > 5 KSP Residual norm 2.725851091482e-13 > > > > mpirun -np 1 ./extest -ksp_monitor -pc_type composite -pc_composite_pcs > none,none -pc_composite_type multiplicative -ksp_norm_type unpreconditioned > > 0 KSP Residual norm 1.414213562373e+00 > > 1 KSP Residual norm 1.290994448736e+00 > > 2 KSP Residual norm 1.249516035344e+00 > > 3 KSP Residual norm 4.836894336642e-01 > > 4 KSP Residual norm 1.467306491390e-01 > > 5 KSP Residual norm 9.881776494390e-14 > >
