In summary, with "fieldsplit_3_pc_type": "lu", "fieldsplit_3_ksp_type": "preonly" the solver diverges with error: Linear firedrake_0_fieldsplit_3_ solve did not converge due to DIVERGED_PCSETUP_FAILED iterations 0 PCSETUP_FAILED due to FACTOR_NUMERIC_ZEROPIVOT while when I use "fieldsplit_3_pc_type": "none", "fieldsplit_3_ksp_type": "cg" it diverges with 21 KSP preconditioned resid norm 6.927181154729e-09 true resid norm 6.927181154729e-09 ||r(i)||/||b|| 1.371504232582e+04 Linear firedrake_0_fieldsplit_3_ solve did not converge due to DIVERGED_DTOL iterations 21 firedrake.exceptions.ConvergenceError: Nonlinear solve failed to converge after 0 nonlinear iterations. Reason: Inner linear solve failed to converge after 180 iterations with reason: DIVERGED_DTOL On 02/12/16 16:11, Lawrence Mitchell wrote:
On 2 Dec 2016, at 16:01, Anna Kalogirou <a.kalogirou@leeds.ac.uk> wrote:
Linear firedrake_0_fieldsplit_3_ solve did not converge due to DIVERGED_DTOL iterations 35
The option
"fieldsplit_3_pc_factor_shift_type": "nonzero" Given that LU with pivoting ought to invert the block unless it is singular, I think something funky is going on.
Can you additionally run with:
"fieldsplit_3_ksp_monitor_true_residual": True
(In passing, if you're using LU you should probably be setting the ksp_type of these sub solves to "preonly", so you don't bother iterating).
Lawrence _______________________________________________ firedrake mailing list firedrake@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/firedrake