Creating a linear and newton solver

1

Hi everyone,
Hope you are safe. I have a question regarding creating newton solver. Follow is my code:

pc = PETScPreconditioner("ilu")
pc.parameters["ilu"]["fill_level"] = 1

#Create Krylov linear solvers and set parameters

krylov_solver = PETScKrylovSolver("bicgstab", pc)
krylov_solver.parameters["relative_tolerance"] = 1.0e-6
krylov_solver.parameters["error_on_nonconvergence"] = False
krylov_solver.parameters["maximum_iterations"] = 250

#Create newton solver
newton_solver = NewtonSolver(krylov_solver, PETScFactory.instance())
newton_solver.parameters["relative_tolerance"] = 1.0e-6
newton_solver.parameters["absolute_tolerance"] = 1.0e-14
newton_solver.parameters["maximum_iterations"] = 10
newton_solver.parameters["error_on_nonconvergence"] = False

At the beginning, I got an error message for line 2 of my code:

RuntimeError Traceback (most recent call last)
in
2
3 pc = PETScPreconditioner(“ilu”)
----> 4 pc.parameters[“ilu”][“fill_level”] = 1
5
6 #Create Krylov linear solvers and set parameters

~/anaconda3/envs/fenicsproject/lib/python3.8/site-packages/dolfin/parameter/init.py in getitem(self, key)
25 # return np
26 else:
—> 27 raise RuntimeError(“Invalid parameter: {}”.format(key))
28
29

RuntimeError: Invalid parameter: ilu

when I make line 2 as comments, following error appears:

TypeError Traceback (most recent call last)
in
12
13 #Create newton solver
—> 14 newton_solver = NewtonSolver(krylov_solver, PETScFactory.instance())
15 newton_solver.parameters[“relative_tolerance”] = 1.0e-6
16 newton_solver.parameters[“absolute_tolerance”] = 1.0e-14

TypeError: init(): incompatible constructor arguments. The following argument types are supported:
1. dolfin.cpp.nls.NewtonSolver()
2. dolfin.cpp.nls.NewtonSolver(arg0: MPICommWrapper)
3. dolfin.cpp.nls.NewtonSolver(arg0: MPICommWrapper, arg1: dolfin.cpp.la.GenericLinearSolver, arg2: dolfin.cpp.la.GenericLinearAlgebraFactory)

Invoked with: <dolfin.cpp.la.PETScKrylovSolver object at 0x7f496958f7f0>, <dolfin.cpp.la.PETScFactory object at 0x7f49696a5070>

I am using latest version of FEniCS, however, I could not find the solution. Your help would be highly appreciated.

2

The second error can be resolved by choosing the third function signature given in the error message:

newton_solver = NewtonSolver(MPI.comm_world,
                             krylov_solver, PETScFactory.instance())

I’m not sure what the best way to resolve the first error is, although you can use the petsc4py API to set arbitrary PETSc options.

3

Thanks very much David for your great help. Actually I have some main problems to convert my code to become compatible with newest version of FEniCS. Again Thanks a lot.