They are all different iteration patterns. They definitely should present different residual results
> On Sep 29, 2017, at 8:19 AM, Xiangdong <[email protected]> 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
