> On 12 Jul 2022, at 2:04 PM, Mark Adams <[email protected]> wrote:
>
> It looks like the RHS is zero in the 2nd case (0 KSP unpreconditioned resid
> norm 0.000000000000e+00), but the true residual is the same.
>
> It looks like you added "nest_subvec" to our example.
It’s a new (dumb) example (ex1111).
> You can start by looking at the vectors with -vec_view (there is code that
> you can view vectors explicitly in your code to get more control if this is
> too noisy)
The Vec are exactly the same (as reported by -ksp_view_rhs) in both cases.
> You could send us the diffs in ex111. We may be able to see something wrong.
I believe there is something weird inside KSPGMRES + PCFIELDSPLIT + right
preconditioning.
Because if I switch to KSPHPDDM implementation of GMRES, then all is good.
In the below traces, I switched VecSet(part of RHS,0.0) to VecSet(part of
RHS,1.0) in ex1111.c to make the error more visible.
Thanks,
Pierre
$ ./ex1111 -pc_type fieldsplit -ksp_converged_reason -fieldsplit_pc_type lu
-ksp_pc_side right -ksp_view_final_residual -nest_subvec false -ksp_view_rhs
-ksp_view_solution
Linear solve did not converge due to DIVERGED_BREAKDOWN iterations 30 < garbage
KSP final norm of residual 1.75544 < garbage
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
0.720032
0.061794
0.0100223
0.144639
0.397778
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1.
1.
1.
1.
1.
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1.73518 < garbage
2.07583e-16
-8.13135e-16
-4.24749e-17
8.18337e-16
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
-1.73518 < garbage
-1.73518 < garbage
-1.73518 < garbage
-1.73518 < garbage
-1.73518 < garbage
$ ./ex1111 -pc_type fieldsplit -ksp_converged_reason -fieldsplit_pc_type lu
-ksp_pc_side right -ksp_view_final_residual -nest_subvec false -ksp_view_rhs
-ksp_view_solution -ksp_type hpddm
Linear solve converged due to CONVERGED_RTOL iterations 1 < correct
KSP final norm of residual 7.89955e-16
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
0.720032
0.061794
0.0100223
0.144639
0.397778
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1.
1.
1.
1.
1.
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1. < correct
1.79841e-18
-5.45696e-17
8.83987e-18
2.82354e-17
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
-1. < correct
-1. < correct
-1. < correct
-1. < correct
-1. < correct
$ ./ex1111 -pc_type fieldsplit -ksp_converged_reason -fieldsplit_pc_type lu
-ksp_pc_side right -ksp_view_final_residual -nest_subvec true -ksp_view_rhs
-ksp_view_solution
Linear solve converged due to CONVERGED_RTOL iterations 1 < correct
KSP final norm of residual 2.74152e-16
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
0.720032
0.061794
0.0100223
0.144639
0.397778
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1.
1.
1.
1.
1.
Vec Object: 1 MPI process
type: nest
VecNest, rows=2, structure:
(0) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
1. < correct
-3.75571e-17
2.51808e-16
7.69081e-18
-2.65477e-16
(1) : type=seq, rows=5
Vec Object: 1 MPI process
type: seq
-1. < correct
-1. < correct
-1. < correct
-1. < correct
-1. < correct
> Mark
>
> On Mon, Jul 11, 2022 at 2:17 PM Pierre Jolivet <[email protected]
> <mailto:[email protected]>> wrote:
> Hello,
> Could anyone help me understand what is going on in the following example,
> please?
> I have a VecNest.
> I either: a) initialize all values to 0.0, then set a specific part of the
> vector to nonzero or b) initialize a part of the vector to 0.0 and set the
> other part to nonzero.
> I don’t see why a) and b) produce different results.
>
> $ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual
> -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right
> -ksp_view_final_residual -nest_subvec true
> 0 KSP unpreconditioned resid norm 8.375635517980e-01 true resid norm
> 8.375635517980e-01 ||r(i)||/||b|| 1.000000000000e+00
> 1 KSP unpreconditioned resid norm 4.748816884247e-01 true resid norm
> 4.748816884247e-01 ||r(i)||/||b|| 5.669798875623e-01
> 2 KSP unpreconditioned resid norm 4.713006778679e-01 true resid norm
> 4.713006778679e-01 ||r(i)||/||b|| 5.627043784990e-01
> 3 KSP unpreconditioned resid norm 7.092979927129e-02 true resid norm
> 7.092979927129e-02 ||r(i)||/||b|| 8.468587144106e-02
> 4 KSP unpreconditioned resid norm 1.457836310255e-02 true resid norm
> 1.457836310255e-02 ||r(i)||/||b|| 1.740567992870e-02
> 5 KSP unpreconditioned resid norm 1.625040500524e-14 true resid norm
> 1.633468028779e-14 ||r(i)||/||b|| 1.950261595401e-14
> Linear solve converged due to CONVERGED_RTOL iterations 5
> KSP final norm of residual 1.63347e-14
> $ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual
> -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right
> -ksp_view_final_residual -nest_subvec false
> 0 KSP unpreconditioned resid norm 0.000000000000e+00 true resid norm
> 8.375635517980e-01 ||r(i)||/||b|| inf
> Linear solve converged due to CONVERGED_ATOL iterations 0
> KSP final norm of residual 0.837564
>
> Thanks,
> Pierre
>
