Dear all, I'm debugging my application in which I'm trying to use the FIELDSPLIT preconditioner for solving a 2x2 block matrix.
Currently I'm testing the preconditioner on a decoupled system where I solve two identical and independent Poisson problems. Using the default fieldsplit type (multiplicative), I'm expecting the method to be equivalent to a Block Jacobi solver. Setting -ksp_rtol 1e-6 while using gmres/hypre on each subblock with -fieldsplit_0_ksp_rtol 1e-12 -fieldsplit_1_ksp_rtol 1e-12 I'm expecting to converge in 1 iteration with a single solve for each block. Asking to output the iteration count for the subblocks with -ksp_converged_reason -fieldsplit_0_ksp_converged_reason -fieldsplit_1_ksp_converged_reason revealed that the outer solver converges in 1 iteration, but each block is solved for 3 times. This is the output I get: Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 0 KSP preconditioned resid norm 9.334948012657e+01 true resid norm 1.280164130222e+02 ||r(i)||/||b|| 1.000000000000e+00 Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 1 KSP preconditioned resid norm 1.518151977611e-11 true resid norm 8.123270435936e-12 ||r(i)||/||b|| 6.345491366429e-14 Linear solve converged due to CONVERGED_RTOL iterations 1 Are the subblocks actually solved for multiple times at every outer iteration? Thanks for the help, Simone
