/// <summary>
/// Adjusts the current parameters with specified gradient and learning rate.
/// </summary>
/// <param name="node">The node.</param>
/// <param name="bDelta">The bias delta values.</param>
/// <param name="wDelta">The weight delta values.</param>
/// <param name="learningRate">The learning rate.</param>
public override void AdjustParameters(Core.Data.LinkedListNode <NnLayer> node, double[][] bDelta, double[][] wDelta, double learningRate)
{
const int rowIndex = 0;
for (var i = 0; i < _biasVelocities[node.Depth][0].Length; i++)
{
_biasVelocities[node.Depth][rowIndex][i] = _momentum * _biasVelocities[node.Depth][rowIndex][i] + bDelta[rowIndex][i];
}
for (var i = 0; i < _weightVelocities[node.Depth].Length; i++)
{
for (var j = 0; j < _weightVelocities[node.Depth][0].Length; j++)
{
_weightVelocities[node.Depth][i][j] = _momentum * _weightVelocities[node.Depth][i][j] + wDelta[i][j];
}
}
base.AdjustParameters(node, _biasVelocities[node.Depth], _weightVelocities[node.Depth], learningRate);
}
/// <summary>
/// Peforms the backpropagatin algorithm.
/// </summary>
/// <param name="predictions">The predictions.</param>
/// <param name="oneHots">The one hot values.</param>
public virtual void Backpropagate(double[][] predictions, int[] oneHots)
{
ProcessCaches(oneHots);
double[][] gradients = CalculateOutputDerivative(predictions, oneHots);
for (var i = 0; i < predictions.Length; i++)
{
double[][] currentGradient = gradients[i].AsMatrix();
Core.Data.LinkedListNode <NnLayer> currentLayer = _neuralNetwork.Layers.Last;
while (currentLayer != null)
{
double[][] delta = currentGradient;
if (PipelineSettings.Instance.CanPerformDropout && currentLayer.Next != null)
{
delta = delta.DotProduct(PipelineSettings.Instance.DropoutVectors[currentLayer.Depth]);
}
// We don't multiply with the weighed sum derivative for the last layer in the network.
if (currentLayer.Depth < _neuralNetwork.Layers.Count - 1)
{
delta = delta.HadamardProduct(_weightedSumDerivatives[currentLayer.Depth][i].AsMatrix());
}
double[][] activation = _activations[currentLayer.Depth][i].AsMatrix();
double[][] wDelta = activation.Transpose().Multiply(delta);
AdjustParameters(currentLayer, delta, wDelta, _neuralNetwork.LearningRate);
currentGradient = currentLayer.Value.BackpropagateError(delta);
currentLayer = currentLayer.Previous;
}
}
}
/// <summary>
/// Calculates the weighted sum derivatives and activation caches in advance.
/// </summary>
/// <param name="oneHots">The one hot values.</param>
private void ProcessCaches(int[] oneHots)
{
var wSumDerivs = new List <double[][]>();
var activationCaches = new List <double[][]>();
Core.Data.LinkedListNode <NnLayer> currentLayer = _neuralNetwork.Layers.First;
while (currentLayer != null)
{
double[][] wSumDeriv = WeightedSumDerivative(currentLayer.Value.ActivationFunction, currentLayer.Depth, oneHots);
wSumDerivs.Add(wSumDeriv);
double[][] activationCache = _neuralNetwork.ActivationCache[currentLayer.Depth];
activationCaches.Add(activationCache);
currentLayer = currentLayer.Next;
}
_weightedSumDerivatives = wSumDerivs;
_activations = activationCaches;
}
/// <summary>
/// Adjusts the current parameters with specified gradient and learning rate.
/// </summary>
/// <param name="node">The node.</param>
/// <param name="bDelta">The bias delta values.</param>
/// <param name="wDelta">The weight delta values.</param>
/// <param name="learningRate">The learning rate.</param>
public virtual void AdjustParameters(Core.Data.LinkedListNode <NnLayer> node, double[][] bDelta, double[][] wDelta, double learningRate)
{
node.Value.BiasVector.AdjustValue(bDelta, learningRate);
node.Value.WeightMatrix.AdjustValue(wDelta, learningRate);
}
