--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/algorithms/aa.py	Mon Oct 27 17:26:00 2008 -0400
@@ -0,0 +1,108 @@
+
+import theano
+from theano import tensor as T
+from theano.tensor import nnet as NN
+import numpy as N
+
+class AutoEncoder(theano.FancyModule):
+
+    def __init__(self, input = None, regularize = True, tie_weights = True):
+        super(AutoEncoder, self).__init__()
+
+        # MODEL CONFIGURATION
+        self.regularize = regularize
+        self.tie_weights = tie_weights
+
+        # ACQUIRE/MAKE INPUT
+        if not input:
+            input = T.matrix('input')
+        self.input = theano.External(input)
+
+        # HYPER-PARAMETERS
+        self.lr = theano.Member(T.scalar())
+
+        # PARAMETERS
+        self.w1 = theano.Member(T.matrix())
+        if not tie_weights:
+            self.w2 = theano.Member(T.matrix())
+        else:
+            self.w2 = self.w1.T
+        self.b1 = theano.Member(T.vector())
+        self.b2 = theano.Member(T.vector())
+
+        # HIDDEN LAYER
+        self.hidden_activation = T.dot(input, self.w1) + self.b1
+        self.hidden = self.build_hidden()
+
+        # RECONSTRUCTION LAYER
+        self.output_activation = T.dot(self.hidden, self.w2) + self.b2
+        self.output = self.build_output()
+
+        # RECONSTRUCTION COST
+        self.reconstruction_cost = self.build_reconstruction_cost()
+
+        # REGULARIZATION COST
+        self.regularization = self.build_regularization()
+
+        # TOTAL COST
+        self.cost = self.reconstruction_cost
+        if self.regularize:
+            self.cost = self.cost + self.regularization
+
+        # GRADIENTS AND UPDATES
+        if self.tie_weights:
+            self.params = self.w1, self.b1, self.b2
+        else:
+            self.params = self.w1, self.w2, self.b1, self.b2
+        gradients = T.grad(self.cost, self.params)
+        updates = dict((p, p - self.lr * g) for p, g in zip(self.params, gradients))
+
+        # INTERFACE METHODS
+        self.update = theano.Method(input, self.cost, updates)
+        self.reconstruction = theano.Method(input, self.output)
+        self.representation = theano.Method(input, self.hidden)
+
+    def _instance_initialize(self, obj, input_size = None, hidden_size = None, seed = None, **init):
+        if (input_size is None) ^ (hidden_size is None):
+            raise ValueError("Must specify hidden_size and target_size or neither.")
+        super(AutoEncoder, self)._instance_initialize(obj, **init)
+        if seed is not None:
+            R = N.random.RandomState(seed)
+        else:
+            R = N.random
+        if input_size is not None:
+            sz = (input_size, hidden_size)
+            range = 1/N.sqrt(input_size)
+            obj.w1 = R.uniform(size = sz, low = -range, high = range)
+            if not self.tie_weights:
+                obj.w2 = R.uniform(size = list(reversed(sz)), low = -range, high = range)
+            obj.b1 = N.zeros(hidden_size)
+            obj.b2 = N.zeros(input_size)
+
+    def build_regularization(self):
+        return T.zero() # no regularization!
+
+
+class SigmoidXEAutoEncoder(AutoEncoder):
+
+    def build_hidden(self):
+        return NN.sigmoid(self.hidden_activation)
+
+    def build_output(self):
+        return NN.sigmoid(self.output_activation)
+
+    def build_reconstruction_cost(self):
+        self.reconstruction_cost_matrix = self.input * T.log(self.output) + (1.0 - self.input) * T.log(1.0 - self.output)
+        self.reconstruction_costs = -T.sum(self.reconstruction_cost_matrix, axis=1)
+        return T.sum(self.reconstruction_costs)
+
+    def build_regularization(self):
+        self.l2_coef = theano.Member(T.scalar())
+        if self.tie_weights:
+            return self.l2_coef * T.sum(self.w1 * self.w1)
+        else:
+            return self.l2_coef * T.sum(self.w1 * self.w1) + T.sum(self.w2 * self.w2)
+
+    def _instance_initialize(self, obj, input_size = None, hidden_size = None, **init):
+        init.setdefault('l2_coef', 0)
+        super(SigmoidXEAutoEncoder, self)._instance_initialize(obj, input_size, hidden_size, **init)