__docformat__ = 'restructedtext en' import numpy import theano import theano.tensor as T class HiddenLayer(object): def __init__(self, rng, input, n_in, n_out, W=None, b=None, activation=T.tanh): """ Typical hidden layer of a MLP: units are fully-connected and have sigmoidal activation function. Weight matrix W is of shape (n_in,n_out) and the bias vector b is of shape (n_out,). Hidden unit activation is given by: activation(dot(input,W) + b) :type rng: numpy.random.RandomState :param rng: a random number generator used to initialize weights :type input: theano.tensor.dmatrix :param input: a symbolic tensor of shape (n_examples, n_in) :type n_in: int :param n_in: dimensionality of input :type n_out: int :param n_out: number of hidden units :type activation: theano.Op or function :param activation: Non linearity to be applied in the hidden layer """ self.input = input # `W` is initialized with `W_values` which is uniformely sampled # from sqrt(-6./(n_in+n_hidden)) and sqrt(6./(n_in+n_hidden)) # for tanh activation function # the output of uniform if converted using asarray to dtype # theano.config.floatX so that the code is runable on GPU # Note : optimal initialization of weights is dependent on the # activation function used (among other things). # For example, results presented in [Xavier10] suggest that you # should use 4 times larger initial weights for sigmoid # compared to tanh # We have no info for other functions, so we use the same as # tanh. if W is None: W_values = numpy.asarray( rng.uniform( low=-numpy.sqrt(6. / (n_in + n_out)), high=numpy.sqrt(6. / (n_in + n_out)), size=(n_in, n_out) ), dtype=theano.config.floatX ) if activation == T.nnet.sigmoid: W_values *= 4 W = theano.shared(value=W_values, name='W', borrow=True) if b is None: b_values = numpy.zeros((n_out,), dtype=theano.config.floatX) b = theano.shared(value=b_values, name='b', borrow=True) self.W = W self.b = b lin_output = T.dot(input, self.W) + self.b self.output = ( lin_output if activation is None else activation(lin_output) ) # parameters of the model self.params = [self.W, self.b] def reset_weight(self, params): self.W.set_value(params[0]) self.b.set_value(params[1]) def reset_weight_by_rate(self, rate): if rate != 0: self.W.set_value(self.W.get_value() / rate) self.b.set_value(self.b.get_value() / rate)