Populate dFdm_cache

Author: Melina97

firedrake/adjoint/blocks.py

@@ -233,6 +233,7 @@ def evaluate_adj_component(self, inputs, adj_inputs, block_variable, idx, prepar
         else:
             dFdm = -firedrake.derivative(self.lhs, c, trial_function)
             dFdm = firedrake.adjoint(dFdm)
+            self._dFdm_cache[c] = dFdm
 
         # Replace the form coefficients with checkpointed values.
         replace_map = self._replace_map(dFdm)