public static Network BuildNetwork(Random random,
ICostFunction costFunction, IRegularizationFunction regularizationFunction,
WeightIntializerType weightIntializerType,
DropoutLayerOptions dropoutLayerOptions,
int inputNeuronCount, int outputNeuronCount, params int[] hiddenLayerCounts)
{
Network network = new Network(costFunction, regularizationFunction,
dropoutLayerOptions, random);
network.InputLayer = InputLayer.BuildInputLayer(null, inputNeuronCount, random);
Layer previousLayer = network.InputLayer;
int dropoutLayerIndex = 1;
bool isDropoutLayer = false;
IWeightBuilder weightBuilder = null;
for (int c = 0; c < hiddenLayerCounts.Length; c++)
{
isDropoutLayer = dropoutLayerOptions.DropoutLayerIndices.Contains(dropoutLayerIndex);
int currentLayerCount = hiddenLayerCounts[c];
switch (weightIntializerType)
{
case WeightIntializerType.RandomGaussianWithNeuronCount:
weightBuilder = new RandomGaussianWithNeuronCount(previousLayer.Neurons.Count, 0, random);
break;
case WeightIntializerType.RandomNormal:
weightBuilder = new RandomGaussian(0, 1, random);
break;
}
HiddenLayer hiddenLayer = HiddenLayer.BuildHiddenLayer(weightBuilder, previousLayer,
currentLayerCount, isDropoutLayer ? dropoutLayerOptions.ProbabilityOfDropout : 0, random);
network.HiddenLayers.Add(hiddenLayer);
previousLayer = hiddenLayer;
dropoutLayerIndex++;
}
isDropoutLayer = dropoutLayerOptions.DropoutLayerIndices.Contains(dropoutLayerIndex);
switch (weightIntializerType)
{
case WeightIntializerType.RandomGaussianWithNeuronCount:
weightBuilder = new RandomGaussianWithNeuronCount(previousLayer.Neurons.Count, 0, random);
break;
case WeightIntializerType.RandomNormal:
weightBuilder = new RandomGaussian(0, 1, random);
break;
}
network.OutputLayer = OutputLayer.BuildOutputLayer(weightBuilder, (HiddenLayer)previousLayer,
outputNeuronCount, isDropoutLayer ? dropoutLayerOptions.ProbabilityOfDropout : 0, random);
return(network);
}
public static OutputLayer BuildOutputLayer(IWeightBuilder weightBuilder,
HiddenLayer previousLayer, int numberOfNeurons, double probabilityOfDropout, Random random)
{
OutputLayer toReturn = new OutputLayer(numberOfNeurons, probabilityOfDropout, random);
for (int c = 0; c < numberOfNeurons; c++)
{
toReturn.Neurons.Add(Neuron.BuildNeuron(weightBuilder, previousLayer));
}
return(toReturn);
}
public double Backpropagation(double[] expectedValues)
{
double totalNetworkCost = 0.0;
// Compute error for the output neurons to get the ball rolling.
// See https://github.com/kwende/CSharpNeuralNetworkExplorations/blob/master/Explorations/SimpleMLP/Documentation/OutputNeuronErrors.png
for (int d = 0; d < expectedValues.Length; d++)
{
Neuron outputNeuronBeingExamined = OutputLayer.Neurons[d];
double expectedOutput = expectedValues[d];
double actualOutput = outputNeuronBeingExamined.Activation;
double actualInput = outputNeuronBeingExamined.TotalInput;
double cost = _costFunction.Compute(expectedOutput, actualOutput);
totalNetworkCost += cost;
double errorRelativeToActivation =
(_costFunction.ComputeDerivativeWRTActivation(actualOutput, expectedOutput));
double errorWrtToNeuron = errorRelativeToActivation * Math.Sigmoid.ComputeDerivative(actualInput);
outputNeuronBeingExamined.AddError(errorWrtToNeuron);
for (int e = 0; e < outputNeuronBeingExamined.UpstreamDendrites.Count; e++)
{
Dendrite dendrite = outputNeuronBeingExamined.UpstreamDendrites[e];
Neuron upstreamNeuron = (Neuron)dendrite.UpStreamNeuron;
double errorRelativeToWeight = (errorWrtToNeuron * upstreamNeuron.Activation);
dendrite.AddError(errorRelativeToWeight);
}
}
// Compute error for each neuron in each layer moving backwards (backprop).
for (int d = HiddenLayers.Count - 1; d >= 0; d--)
{
HiddenLayer hiddenLayer = HiddenLayers[d];
for (int e = 0; e < hiddenLayer.Neurons.Count; e++)
{
Neuron thisNeuron = (Neuron)hiddenLayer.Neurons[e];
double dropoutBit = hiddenLayer.DropOutMask[e];
double input = thisNeuron.TotalInput;
double errorSum = 0.0;
List <Dendrite> downStreamDendrites = thisNeuron.DownstreamDendrites;
for (int f = 0; f < downStreamDendrites.Count; f++)
{
Dendrite currentDendrite = downStreamDendrites[f];
Neuron downStreamNeuron = currentDendrite.DownStreamNeuron;
double delta = downStreamNeuron.CurrentNeuronError;
double weight = currentDendrite.Weight;
errorSum += delta * weight;
}
double errorWrtToThisNeuron = errorSum * Math.Sigmoid.ComputeDerivative(input) * dropoutBit;
thisNeuron.AddError(errorWrtToThisNeuron);
for (int f = 0; f < thisNeuron.UpstreamDendrites.Count; f++)
{
Dendrite dendrite = thisNeuron.UpstreamDendrites[f];
Neuron upstreamNeuron = (Neuron)dendrite.UpStreamNeuron;
double errorRelativeToWeight = (errorWrtToThisNeuron * upstreamNeuron.Activation);
dendrite.AddError(errorRelativeToWeight);
}
}
}
return(totalNetworkCost);
}
