Support listlike checkpoints (#170)

* Support listlike checkpoints.

CHANGELOG.md

@@ -1,5 +1,9 @@
 # FEniCS-preCICE adapter changelog
 
+## latest
+
+* Additionally support checkpoints being provided as a list or tuple (of FEniCS Functions). [#170](https://github.com/precice/fenics-adapter/pull/170)
+
 ## 2.0.0
 
 * Drop support for preCICE 2.x version, as this is a breaking release.

fenicsprecice/fenicsprecice.py

@@ -432,14 +432,14 @@ def initialize(self, coupling_subdomain, read_function_space=None, write_object=
 
         self._participant.initialize()
 
-    def store_checkpoint(self, user_u, t, n):
+    def store_checkpoint(self, payload, t, n):
         """
         Defines an object of class SolverState which stores the current state of the variable and the time stamp.
 
         Parameters
         ----------
-        user_u : FEniCS Function
-            Current state of the physical variable of interest for this participant.
+        payload : fenics.function or a list of fenics.functions
+            Current state of the physical variable(s) of interest for this participant.
         t : double
             Current simulation time.
         n : int
@@ -449,10 +449,7 @@ def store_checkpoint(self, user_u, t, n):
             assert (self.is_time_window_complete())
 
         logger.debug("Store checkpoint")
-        my_u = user_u.copy()
-        # making sure that the FEniCS function provided by user is not directly accessed by the Adapter
-        assert (my_u != user_u)
-        self._checkpoint = SolverState(my_u, t, n)
+        self._checkpoint = SolverState(payload, t, n)
 
     def retrieve_checkpoint(self):
         """

fenicsprecice/solverstate.py

@@ -1,36 +1,43 @@
 class SolverState:
-    def __init__(self, u, t, n):
+    def __init__(self, payload, t, n):
         """
-        Solver state consists of a value u, associated time t and the timestep n
+        Solver state consists of a payload (either a single fenics.Function or a list of several fenics.Functions), associated time t and the timestep n
 
         Parameters
         ----------
-        u : Object of class dolfin.functions.function.Function
-            FEniCS function related to the field during each coupling iteration.
+        payload : A fenics.Function or a list of fenics.Functions
+            Describes the state of the solver.
         t : double
             Time stamp.
         n : int
             Iteration number.
         """
-        self.u = u
+        try:
+            self.payload = payload.copy()
+        except AttributeError:  # if .copy() does not exist, it probably is a list
+            self.payload = [item.copy() for item in payload]
+
         self.t = t
         self.n = n
 
     def get_state(self):
         """
-        Returns the state variables value u, associated time t and timestep n
+        Returns the state variables payload, associated time t and timestep n
 
         Returns
         -------
-        u : Object of class dolfin.functions.function.Function
-            A copy of FEniCS function related to the field during each coupling iteration.
+        payload : A fenics.Function or a list of fenics.Functions
+            Describes the state of the solver.
         t : double
             Time stamp.
         n : int
             Iteration number.
         """
-        return self.u.copy(), self.t, self.n
+        try:
+            return self.payload.copy(), self.t, self.n
+        except AttributeError:  # if .copy() does not exist, it probably is a list
+            return [item.copy() for item in self.payload], self.t, self.n
 
     def print_state(self):
-        u, t, n = self.get_state()
-        return print("u={u}, t={t}, n={n}".format(u=u, t=t, n=n))
+        payload, t, n = self.get_state()
+        return print(f"payload={payload}, t={t}, n={n}")