Merge remote-tracking branch 'origin/master' into dolci/fix_sphinx_fail

docs/source/documentation/index.rst

@@ -361,8 +361,7 @@ a tape. The current working tape can be set and retrieved with the functions :py
 :py:func:`get_working_tape`.
 
 Annotation can be temporarily disabled using :py:func:`pause_annotation` and enabled again using :py:func:`continue_annotation`.
-Note that if you call :py:func:`pause_annotation` twice, then :py:func:`continue_annotation` must be called twice
-to enable annotation. Due to this, the recommended annotation control functions are :py:class:`stop_annotating` and :py:func:`no_annotations`.
+It is recommended to use :py:class:`stop_annotating` and :py:func:`no_annotations` for annotation control.
 :py:class:`stop_annotating` is a context manager and should be used as follows
 
 .. code-block:: python

docs/source/documentation/pyadjoint_api.rst

@@ -19,6 +19,8 @@ Core classes
     .. automethod:: add_block
     .. automethod:: visualise
     .. autoproperty:: progress_bar
+    .. automethod:: end_timestep
+    .. automethod:: timestepper
 
 .. autoclass:: Block
 

pyadjoint/block.py

@@ -50,7 +50,7 @@ def add_dependency(self, dep, no_duplicates=False):
 
         """
         if not no_duplicates or dep.block_variable not in self._dependencies:
-            dep._ad_will_add_as_dependency()
+            dep.block_variable.will_add_as_dependency()
             self._dependencies.append(dep.block_variable)
 
     def get_dependencies(self):

pyadjoint/block_variable.py

@@ -1,4 +1,4 @@
-from .tape import no_annotations
+from .tape import no_annotations, get_working_tape
 
 
 class BlockVariable(object):
@@ -16,6 +16,10 @@ def __init__(self, output):
         self.floating_type = False
         # Helper flag for use during tape traversals.
         self.marked_in_path = False
+        # By default assume the variable is created externally to the tape.
+        self.creation_timestep = -1
+        # The timestep during which this variable was last used as an input.
+        self.last_use = -1
 
     def add_adj_output(self, val):
         if self.adj_value is None:
@@ -59,13 +63,23 @@ def saved_output(self):
 
     def will_add_as_dependency(self):
         overwrite = self.output._ad_will_add_as_dependency()
-        overwrite = False if overwrite is None else overwrite
-        self.save_output(overwrite=overwrite)
+        overwrite = bool(overwrite)
+        tape = get_working_tape()
+        if self.last_use < tape.latest_checkpoint:
+            self.save_output(overwrite=overwrite)
+        tape.add_to_checkpointable_state(self, self.last_use)
+        self.last_use = tape.latest_timestep
 
     def will_add_as_output(self):
+        tape = get_working_tape()
+        self.creation_timestep = tape.latest_timestep
+        self.last_use = self.creation_timestep
         overwrite = self.output._ad_will_add_as_output()
-        overwrite = True if overwrite is None else overwrite
-        self.save_output(overwrite=overwrite)
+        overwrite = bool(overwrite)
+        if not overwrite:
+            self._checkpoint = None
+        if tape._eagerly_checkpoint_outputs:
+            self.save_output()
 
     def __str__(self):
         return str(self.output)