/// <summary>
/// Calculates error values for all neurons of the network
/// </summary>
///
/// <param name="desiredOutput">Desired output vector</param>
///
/// <returns>Returns summary squared error of the last layer divided by 2</returns>
///
private double CalculateError(double[] desiredOutput)
{
// current and the next layers
ActivationLayer layer, layerNext;
// current and the next errors arrays
double[] errors, errorsNext;
// error values
double error = 0, e, sum;
// neuron's output value
double output;
// layers count
int layersCount = network.LayersCount;
// assume, that all neurons of the network have the same activation function
IActivationFunction function = network[0][0].ActivationFunction;
// calculate error values for the last layer first
layer = network[layersCount - 1];
errors = neuronErrors[layersCount - 1];
for (int i = 0, n = layer.NeuronsCount; i < n; i++)
{
output = layer[i].Output;
// error of the neuron
e = desiredOutput[i] - output;
// error multiplied with activation function's derivative
errors[i] = e * function.Derivative2(output);
// squre the error and sum it
error += (e * e);
}
// calculate error values for other layers
for (int j = layersCount - 2; j >= 0; j--)
{
layer = network[j];
layerNext = network[j + 1];
errors = neuronErrors[j];
errorsNext = neuronErrors[j + 1];
// for all neurons of the layer
for (int i = 0, n = layer.NeuronsCount; i < n; i++)
{
sum = 0.0;
// for all neurons of the next layer
for (int k = 0, m = layerNext.NeuronsCount; k < m; k++)
{
sum += errorsNext[k] * layerNext[k][i];
}
errors[i] = sum * function.Derivative2(layer[i].Output);
}
}
// return squared error of the last layer divided by 2
return(error / 2.0);
}
/// <summary>
/// Calculates error values for all neurons of the network.
/// </summary>
///
/// <param name="desiredOutput">Desired output vector.</param>
///
/// <returns>Returns summary squared error of the last layer divided by 2.</returns>
///
private double CalculateError(double[] desiredOutput)
{
double error = 0;
int layersCount = network.Layers.Length;
// assume, that all neurons of the network have the same activation function
IActivationFunction function = (network.Layers[0].Neurons[0] as ActivationNeuron).ActivationFunction;
// calculate error values for the last layer first
ActivationLayer layer = network.Layers[layersCount - 1] as ActivationLayer;
double[] layerDerivatives = neuronErrors[layersCount - 1];
for (int i = 0; i < layer.Neurons.Length; i++)
{
double output = layer.Neurons[i].Output;
double e = output - desiredOutput[i];
layerDerivatives[i] = e * function.Derivative2(output);
error += (e * e);
}
// calculate error values for other layers
for (int j = layersCount - 2; j >= 0; j--)
{
layer = network.Layers[j] as ActivationLayer;
layerDerivatives = neuronErrors[j];
ActivationLayer layerNext = network.Layers[j + 1] as ActivationLayer;
double[] nextDerivatives = neuronErrors[j + 1];
// for all neurons of the layer
for (int i = 0, n = layer.Neurons.Length; i < n; i++)
{
double sum = 0.0;
for (int k = 0; k < layerNext.Neurons.Length; k++)
{
sum += nextDerivatives[k] * layerNext.Neurons[k].Weights[i];
}
layerDerivatives[i] = sum * function.Derivative2(layer.Neurons[i].Output);
}
}
// return squared error of the last layer divided by 2
return(error / 2.0);
}
/// <summary>
/// Runs learning iteration
/// </summary>
///
/// <param name="input">input vector</param>
/// <param name="output">desired output vector</param>
///
/// <returns>Returns squared error divided by 2</returns>
///
/// <remarks>Runs one learning iteration and updates neuron's
/// weights.</remarks>
///
public double Run(double[] input, double[] output)
{
// compute output of network
double[] networkOutput = network.Compute(input);
// get the only layer of the network
ActivationLayer layer = network[0];
// get activation function of the layer
IActivationFunction activationFunction = layer[0].ActivationFunction;
// summary network absolute error
double error = 0.0;
// update weights of each neuron
for (int j = 0, k = layer.NeuronsCount; j < k; j++)
{
// get neuron of the layer
ActivationNeuron neuron = layer[j];
// calculate neuron's error
double e = output[j] - networkOutput[j];
// get activation function's derivative
double functionDerivative = activationFunction.Derivative2(networkOutput[j]);
// update weights
for (int i = 0, n = neuron.InputsCount; i < n; i++)
{
neuron[i] += learningRate * e * functionDerivative * input[i];
}
// update threshold value
neuron.Threshold += learningRate * e * functionDerivative;
// sum error
error += (e * e);
}
return(error / 2);
}
