neural_network_multilayer_Layers_2.py

#Two Layer Nueral Networks
#Adapted from Two Layer Network https://github.com/miloharper/multi-layer-neural-network/blob/master/LICENSE.md with Slight Modifications by Gorla Praveen

#The MIT License (MIT)

#Copyright (c) 2015 Milo Spencer-Harper

#Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

#The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


from numpy import exp, array, random, dot


class NeuronLayer():
    def __init__(self, number_of_neurons, number_of_inputs_per_neuron):
        self.synaptic_weights = 2 * random.random((number_of_inputs_per_neuron, number_of_neurons)) - 1


class NeuralNetwork():
    def __init__(self, layer1, layer2):
        self.layer1 = layer1
        self.layer2 = layer2

    # The Sigmoid function, which describes an S shaped curve.
    # We pass the weighted sum of the inputs through this function to
    # normalise them between 0 and 1.
    def __sigmoid(self, x):
        return 1 / (1 + exp(-x))

    # The derivative of the Sigmoid function.
    # This is the gradient of the Sigmoid curve.
    # It indicates how confident we are about the existing weight.
    def __sigmoid_derivative(self, x):
        return x * (1 - x)

    # We train the neural network through a process of trial and error.
    # Adjusting the synaptic weights each time.
    def train(self, training_set_inputs, training_set_outputs, number_of_training_iterations):
        for iteration in xrange(number_of_training_iterations):
            # Pass the training set through our neural network
            output_from_layer_1, output_from_layer_2 = self.think(training_set_inputs)

            # Calculate the error for layer 2 (The difference between the desired output
            # and the predicted output).
            layer2_error = training_set_outputs - output_from_layer_2
            layer2_delta = layer2_error * self.__sigmoid_derivative(output_from_layer_2)

            # Calculate the error for layer 1 (By looking at the weights in layer 1,
            # we can determine by how much layer 1 contributed to the error in layer 2).
            layer1_error = layer2_delta.dot(self.layer2.synaptic_weights.T)
            layer1_delta = layer1_error * self.__sigmoid_derivative(output_from_layer_1)

            # Calculate how much to adjust the weights by
            layer1_adjustment = training_set_inputs.T.dot(layer1_delta)
            layer2_adjustment = output_from_layer_1.T.dot(layer2_delta)

            # Adjust the weights.
            self.layer1.synaptic_weights += layer1_adjustment
            self.layer2.synaptic_weights += layer2_adjustment

    # The neural network thinks.
    def think(self, inputs):
        output_from_layer1 = self.__sigmoid(dot(inputs, self.layer1.synaptic_weights))
        output_from_layer2 = self.__sigmoid(dot(output_from_layer1, self.layer2.synaptic_weights))
        return output_from_layer1, output_from_layer2

    # The neural network prints its weights
    def print_weights(self):
        print "    Layer 1 (4 neurons, each with 3 inputs): "
        print self.layer1.synaptic_weights
        print "    Layer 2 (1 neuron, with 4 inputs):"
        print self.layer2.synaptic_weights

if __name__ == "__main__":

    #Seed the random number generator
    random.seed(1)

    # Create layer 1 (4 neurons, each with 3 inputs)
    layer1 = NeuronLayer(4, 3)

    # Create layer 2 (a single neuron with 4 inputs)
    layer2 = NeuronLayer(1, 4)

    # Combine the layers to create a neural network
    neural_network = NeuralNetwork(layer1, layer2)

    print "Stage 1) Random starting synaptic weights: "
    neural_network.print_weights()

    # The training set. We have 7 examples, each consisting of 3 input values
    # and 1 output value.
    training_set_inputs = array([[0, 0, 1], [0, 1, 1], [1, 0, 1], [0, 1, 0], [1, 0, 0], [1, 1, 1], [0, 0, 0]])
    training_set_outputs = array([[0, 1, 1, 1, 1, 0, 0]]).T

    # Train the neural network using the training set.
    # Do it 60,000 times and make small adjustments each time.
    neural_network.train(training_set_inputs, training_set_outputs, 60000)

    print "Stage 2) New synaptic weights after training: "
    neural_network.print_weights()

    # Test the neural network with a new situation.
    print "Stage 3) Considering a new situation [1, 1, 0] -> ?: "
    hidden_state, output = neural_network.think(array([1, 1, 0]))
print "Printing Hidden Layer 1 Output"
print hidden_state
print "Printing Final Output"
print output