Add support for objective function in SNES

firedrake/solving_utils.py

@@ -231,6 +231,7 @@ def __init__(self, problem,
         self.pmatfree = pmatfree
         self.F = problem.F
         self.J = problem.J
+        self.E = problem.E
 
         # For Jp to equal J, bc.Jp must equal bc.J for all EquationBC objects.
         Jp_eq_J = problem.Jp is None and all(bc.Jp_eq_J for bc in problem.bcs)
@@ -261,6 +262,12 @@ def __init__(self, problem,
 
             self.F -= problem.compute_bc_lifting(self.J, self._bc_residual)
 
+        self._assemble_objective = lambda *args, **kwargs: args
+        if self.E:
+            self._assemble_objective = get_assembler(self.E,
+                                                     form_compiler_parameters=self.fcp,
+                                                     ).assemble
+
         self._assemble_residual = get_assembler(self.F, bcs=self.bcs_F,
                                                 form_compiler_parameters=self.fcp,
                                                 zero_bc_nodes=pre_apply_bcs,
@@ -342,6 +349,12 @@ def transfer_manager(self, manager):
             raise ValueError("Must set transfer manager before first use.")
         self._transfer_manager = manager
 
+    def set_objective(self, snes):
+        if self._problem.E:
+            snes.setObjective(self.form_objective)
+        else:
+            snes.setObjective(None)
+
     def set_function(self, snes):
         r"""Set the residual evaluation function"""
         with self._F.dat.vec_wo as v:
@@ -449,6 +462,27 @@ def split(self, fields):
             splits.append(self.reconstruct(new_problem, options_prefix=options_prefix))
         return self._splits.setdefault(tuple(fields), splits)
 
+    @staticmethod
+    def form_objective(snes, X):
+        r"""Form the objective for this problem
+
+        :arg snes: a PETSc SNES object
+        :arg X: the current guess (a Vec)
+        """
+        dm = snes.getDM()
+        ctx = dmhooks.get_appctx(dm)
+        # X may not be the same vector as the vec behind self._x, so
+        # copy guess in from X.
+        with ctx._x.dat.vec_wo as v:
+            X.copy(v)
+
+        if not ctx.pre_apply_bcs:
+            # Compute DirichletBC residual
+            for bc in ctx._problem.dirichlet_bcs():
+                bc.apply(ctx._bc_residual, u=ctx._x)
+
+        return ctx._assemble_objective(current_state=ctx._x)
+
     @staticmethod
     def form_function(snes, X, F):
         r"""Form the residual for this problem

firedrake/variational_solver.py

@@ -23,7 +23,7 @@
            "NonlinearVariationalSolver"]
 
 
-def check_pde_args(F, J, Jp):
+def check_pde_args(F, J, Jp, E=None):
     if not isinstance(F, (ufl.BaseForm, slate.slate.TensorBase)):
         raise TypeError("Provided residual is a '%s', not a BaseForm or Slate Tensor" % type(F).__name__)
     if len(F.arguments()) != 1:
@@ -36,6 +36,11 @@ def check_pde_args(F, J, Jp):
         raise TypeError("Provided preconditioner is a '%s', not a BaseForm or Slate Tensor" % type(Jp).__name__)
     if Jp is not None and len(Jp.arguments()) != 2:
         raise ValueError("Provided preconditioner is not a bilinear form")
+    if E is not None:
+        if not isinstance(E, (ufl.BaseForm, slate.slate.TensorBase)):
+            raise TypeError("Provided objective is a '%s', not a BaseForm or Slate Tensor" % type(F).__name__)
+        if len(E.arguments()) != 0:
+            raise ValueError("Provided objective is not a linear form")
 
 
 def is_form_consistent(is_linear, bcs):
@@ -52,6 +57,7 @@ class NonlinearVariationalProblem(NonlinearVariationalProblemMixin):
     @NonlinearVariationalProblemMixin._ad_annotate_init
     def __init__(self, F, u, bcs=None, J=None,
                  Jp=None,
+                 objective=None,
                  form_compiler_parameters=None,
                  is_linear=False, restrict=False):
         r"""
@@ -62,6 +68,7 @@ def __init__(self, F, u, bcs=None, J=None,
         :param Jp: a form used for preconditioning the linear system,
                  optional, if not supplied then the Jacobian itself
                  will be used.
+        :param objective: a form used for line-search, optional
         :param dict form_compiler_parameters: parameters to pass to the form
             compiler (optional)
         :is_linear: internally used to check if all domain/bc forms
@@ -79,6 +86,7 @@ def __init__(self, F, u, bcs=None, J=None,
 
         # Use the user-provided Jacobian. If none is provided, derive
         # the Jacobian from the residual.
+        self.E = objective
         self.J = J or ufl_expr.derivative(F, u)
         self.F = F
         self.Jp = Jp
@@ -119,7 +127,7 @@ def __init__(self, F, u, bcs=None, J=None,
         self.Jp_eq_J = Jp is None
 
         # Argument checking
-        check_pde_args(self.F, self.J, self.Jp)
+        check_pde_args(self.F, self.J, self.Jp, E=self.E)
 
         # Store form compiler parameters
         self.form_compiler_parameters = form_compiler_parameters
@@ -304,6 +312,7 @@ def update_diffusivity(current_solution):
         self._work = problem.u_restrict.dof_dset.layout_vec.duplicate()
         self.snes.setDM(problem.dm)
 
+        ctx.set_objective(self.snes)
         ctx.set_function(self.snes)
         ctx.set_jacobian(self.snes)
         ctx.set_nullspace(nullspace, problem.J.arguments()[0].function_space()._ises,
@@ -353,12 +362,13 @@ def solve(self, bounds=None):
            ``vinewtonssls`` or ``vinewtonrsls``.
         """
         # Make sure the DM has this solver's callback functions
+        self._ctx.set_objective(self.snes)
         self._ctx.set_function(self.snes)
         self._ctx.set_jacobian(self.snes)
 
         # Make sure appcontext is attached to every DM from every coefficient and DirichletBC before we solve.
         problem = self._problem
-        forms = (problem.F, problem.J, problem.Jp)
+        forms = (problem.F, problem.J, problem.Jp, problem.E)
         coefficients = utils.unique(chain.from_iterable(form.coefficients() for form in forms if form is not None))
         solution_dm = self.snes.getDM()
         # Grab the unique DMs for this problem

tests/firedrake/deflation/test_bratu.py

@@ -41,3 +41,38 @@ def test_bratu():
 
     (first, second) = deflation.roots
     assert norm(first - second) > 1
+
+
+@pytest.mark.skipcomplex
+def test_bratu_energy():
+    mesh = UnitIntervalMesh(10)
+    V = FunctionSpace(mesh, "CG", 3)
+
+    u = Function(V)
+    v = TestFunction(V)
+    sol1 = Function(V)
+    sol2 = Function(V)
+
+    lmbda = Constant(2)
+
+    E = 0.5 * inner(grad(u), grad(u))*dx + exp(lmbda*u)*dx
+    F = inner(grad(u), grad(v))*dx + lmbda*inner(exp(lmbda*u), v)*dx
+    bcs = DirichletBC(V, 0, "on_boundary")
+    sp = {"snes_monitor": "::ascii_info_detail",
+          "snes_type": "newtontr",
+          "ksp_monitor": None,
+          "ksp_type": "cg",
+          "pc_type": "none"}
+    problem = NonlinearVariationalProblem(F, u, bcs, objective=E)
+    solver = NonlinearVariationalSolver(problem, solver_parameters=sp)
+    solver.solve()
+    sol1.assign(u)
+
+    u.assign(0)
+    sp = {"snes_monitor": "::ascii_info_detail"}
+    problem = NonlinearVariationalProblem(F, u, bcs)
+    solver = NonlinearVariationalSolver(problem, solver_parameters=sp)
+    solver.solve()
+    sol2.assign(u)
+
+    assert norm(sol1 - sol2) < 1.e-8