Add method updates() and member state_updates to MRG_RandomStreams

theano/sandbox/rng_mrg.py

@@ -556,6 +556,13 @@ class GPU_mrg_uniform(mrg_uniform_base):
 class MRG_RandomStreams(object):
     """Module component with similar interface to numpy.random (numpy.random.RandomState)"""
 
+    state_updates = []
+    """A list of pairs of the form (input_r, output_r), representing the
+    update rules of all the random states generated by this RandomStreams"""
+
+    def updates(self):
+        return list(self.state_updates)
+
     def __init__(self, seed=12345, use_cuda=None):
         """
         :type seed: int or list of 6 int.
@@ -627,6 +634,7 @@ class MRG_RandomStreams(object):
     def pretty_return(self, node_rstate, new_rstate, sample):
         sample.rstate = node_rstate
         sample.update = (node_rstate, new_rstate)
+        self.state_updates.append((node_rstate, new_rstate))
         node_rstate.default_update = new_rstate
         return sample