Error in adapting non-linear variational problem while using AdaptiveNonlinearVariationalSolver

3 months ago by
I am trying to solve a coupled set of equations where I solve the first equation using AdaptiveNonlinearVariationalSolver and the second using NonlinearVariationalSolver. after each solution I update the problem by adapting it to new mesh. The code causing the error could be found here:

# Define the non-linear variational problems for phase field and displacement
problem_u = NonlinearVariationalProblem(R_u, uh, BC_u, J_u)
problem_d = NonlinearVariationalProblem(R_d, dh, BC_d, J_d)

# Define the solvers for the non-linear variational problems
solver_u = NonlinearVariationalSolver(problem_u)

M = dh*dx()
tol_M = 1.0e-6
solver_d = AdaptiveNonlinearVariationalSolver(problem_d,M)
# Integrate in time
	while step < max_steps:

		mh = MeshHierarchy(mesh)

		if step < 51:
			dirichlet_val_u_2.t_y = 1.0e-4*step
			dirichlet_val_u_2.t_y = 5.0e-3+1.0e-5*(step-50)

		it = 0 
		# Iterate while solution is converged
		while True:

			# Solve phase field

#			dh_lb.assign( dh )
			check = True
			if check:
				print('in check')
				#mh = mh.refine(cell_markers)
				# adapt to the refined mesh
				dx = Measure("dx",domain = mh.finest())
				ds = Measure("ds",domain = mh.finest())
				adapt(problem_u, mh.finest())
				uh_prev = uh_prev.child()
				uh = uh.child()
				problem_u   = problem_u.child()
				solver_u    = NonlinearVariationalSolver(problem_u.leaf_node())
				adapt(problem_d, mh.finest())
				dh_prev = dh_prev.child()
				dh = dh.child()
				M = dh*dx()
				problem_d   = problem_d.child()
				solver_d   = AdaptiveNonlinearVariationalSolver(problem_d.leaf_node(),M)
				mesh = mesh.child()
				print('out of check')
			diff_d = norm( dh.vector() - dh_prev.vector() )/norm( dh.vector())

			# Solve variational problem
			diff_u = norm( uh.vector() - uh_prev.vector() )/norm( uh.vector())
			diff =  diff_d   + diff_u
			print ('Difference in fields: %.2e (d: %.2e, u: %.2e )' +\
					'Step: %i Iteration: %i Eta: %.2e' ) % (diff,diff_d,diff_u,step,it,eta)

			uh_prev.assign( uh )
			dh_prev.assign( dh )			
When I try to adapt the solver I get the following error:
File "", line 347, in <module>
    solver_d   = AdaptiveNonlinearVariationalSolver(problem_d.leaf_node(),M)
*** Error:   Unable to generate forms required for error control.
*** Reason:  Unknown problem type ("<dolfin.cpp.fem.NonlinearVariationalProblem; proxy of <Swig Object of type 'std::shared_ptr< dolfin::NonlinearVariationalProblem > *' at 0x7fc5702661b0> >").
Any suggestions as to how should we update the problem?
Community: FEniCS Project

1 Answer

3 months ago by
You're using a MixedFunctionSpace (coupled equations), so try M = dh[0]*dx() (cf.
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