add ad-hoc weight-sharing method

onn_core.py

@@ -132,6 +132,7 @@ class Weights:
         self.init = None
         self.allocator = None
         self.regularizer = None
+        self._allocated = False
 
         self.configure(**kwargs)
 
@@ -146,6 +147,8 @@ class Weights:
         return np.prod(self.shape)
 
     def allocate(self, *args, **kwargs):
+        if self._allocated:
+            raise Exception("attempted to allocate existing weights")
         self.configure(**kwargs)
 
         # intentionally not using isinstance
@@ -159,6 +162,8 @@ class Weights:
         self.f = f.reshape(self.shape)
         self.g = g.reshape(self.shape)
 
+        self._allocated = True
+
     def forward(self):
         if self.regularizer is None:
             return 0.0
@@ -482,7 +487,7 @@ class Layer:
         _layer_counters[kind] += 1
         self.name = "{}_{}".format(kind, _layer_counters[kind])
         self.unsafe = False # disables assertions for better performance
-        # TODO: allow weights to be shared across layers.
+        self.shared = False # as in weight sharing
 
     def __str__(self):
         return self.name
@@ -551,6 +556,13 @@ class Layer:
         self.weights[name] = w
         return w
 
+    def share(self, node):
+        self.weights = node.weights # TODO: this should be all it takes.
+        for k, v in self.weights.items():
+            vs = getattr(node, k) # hack: key isn't necessarily attribute name!
+            setattr(self, k, vs)
+        self.shared = True
+
     def clear_grad(self):
         for name, w in self.weights.items():
             w.g[:] = 0
@@ -864,13 +876,13 @@ class Model:
         return self.nodes
 
     def make_weights(self):
-        self.param_count = sum((node.size for node in self.nodes))
+        self.param_count = sum((node.size for node in self.nodes if not node.shared))
         self.W  = np.zeros(self.param_count, dtype=_f)
         self.dW = np.zeros(self.param_count, dtype=_f)
 
         offset = 0
         for node in self.nodes:
-            if node.size > 0:
+            if node.size > 0 and not node.shared:
                 inner_offset = 0
 
                 def allocate(size):
@@ -941,6 +953,7 @@ class Model:
             used[k] = False
 
         nodes = [node for node in self.nodes if node.size > 0]
+        # TODO: support shared weights.
         for node in nodes:
             full_name = str(node).lower()
             for s_name, o_name in node.serialized.items():
@@ -961,6 +974,7 @@ class Model:
         counts = defaultdict(lambda: 0)
 
         nodes = [node for node in self.nodes if node.size > 0]
+        # TODO: support shared weights.
         for node in nodes:
             full_name = str(node).lower()
             grp = f.create_group(full_name)