def get_cost_updates(self, corruption_level, learning_rate):
""" This function computes the cost and the updates for one trainng
step of the dA
Aguments:
corruption_level: the degree to which teh input should be
corrupted. currently the data is not corrupted.
learning_rate : the degree to which the weights should be
altered after a step of gradient descent.
Returns:
The errors and the updates to the parameters.
"""
#tilde_x = self.x
tilde_x = self.get_corrupted_input(self.x, corruption_level)
h = self.get_hidden_values(tilde_x)
z = self.get_reconstructed_input(h)
# in order to calculate L below, i could not use a sparse matrix
# for self.y. as a result, i had to convert it to a dense matrix
# and operate on this new matrix.
# TODO: try to make it work with sparse matrix?
if type(self.y) == T.TensorVariable:
y_mat = self.y
else:
y_mat = sparse.dense_from_sparse(self.y)
# this is the cross-entropy error
#L = -T.sum(self.y * T.log(z) + (one_mat - self.y) * T.log(one_mat - z), axis=1)
#y_prob = y_mat * T.log(z)
#y_not_prob = (1.0 - y_mat)
#z_not_prob = (1.0 - z)
#L = -T.sum(y_prob + y_not_prob * T.log(z_not_prob), axis=1)
L = -T.sum(y_mat * T.log(z) + (1.0 - y_mat) * T.log(1.0 - z), axis=1)
# TODO: add L1 or L2 penalization here?
cost = T.mean(L)
# compute the gradients of the cost of the `dA` with respect
# to its parameters
gparams = T.grad(cost, self.params)
# generate the list of updates
updates = []
for param, gparam in zip(self.params, gparams):
updates.append((param, param - learning_rate * gparam))
return (cost, updates)
def get_reconstruction_errors(self, data):
h = self.get_hidden_values(data)
z = self.get_reconstructed_input(h)
error = z - sparse.dense_from_sparse(data)
return error
def unSparse(self):
for name in self.keys():
self[name] = sparse.dense_from_sparse(self[name])
