//Dato lo strato di partenza, propaga il potenziale d'azione nello strato successivo.
private void propagate(int i, Activation act)
{
int j, k;
double sum; //Accumulatore.
for (j = 0; j < NumPercept[i + 1]; j++) //Scorro i percettroni dello strato successivo.
{
sum = 0; //Azzero l'accumulatore
for (k = 0; k < NumPercept[i]; k++) //Scorro i percettroni dello strato di partenza.
{
sum += layer[i].perceptron[k].getAction() * layer[i].perceptron[k].getSynapsys(j); /* moltiplica potenziale d'azione
* per peso sinaptico della connessione
* fra k e j.*/
}
sum += Bias; //Se non lo capisci non continuare a leggere e ristudiati la teoria prima.
layer[i + 1].perceptron[j].setAction(act.LogisticSigmoid(sum)); /* Applica la funzione di costo e assegna il nuovo
* potenziale d'azione.*/
}
/*per applicare il softmax, decommenta questo segmento.*/
/*if(i == NumLayers - 2)
* act.Softmax(layer[i+1]);*/
}
/// <summary>
/// This method will calculate dC with respect to Z from one of the specified activations
/// then use this dC/dZ to calculate the other derivatives.
/// </summary>
/// <param name="dA">The derivative of the cost function with respect to the activations.</param>
/// <param name="Z">The linear function of the weights biases and previous layers activations.</param>
/// <param name="linearCache">A linear cache obtained from forward prop.</param>
/// <param name="activation">The type of activation to use. Corrosponds with the activation that was used for this layer during forward prop.</param>
/// <param name="lambda">The L2 regularization hyper-parameter.</param>
/// <returns>The derivatives provided from the <see cref="LinearBackward"/> function.</returns>
private Tuple <MatrixVectors, MatrixVectors, MatrixVectors> ActivationsBackward(MatrixVectors dA, MatrixVectors Z, LinearCache linearCache, Activation activation, float lambda)
{
MatrixVectors dZ;
switch (activation)
{
case Activation.Sigmoid:
dZ = SigmoidPrime(dA, Z);
break;
case Activation.ReLu:
dZ = ReLuPrime(dA, Z);
break;
default:
throw new ArgumentOutOfRangeException();
}
return(LinearBackward(dZ, linearCache, lambda));
}
/// <summary>
/// This method runs the linear function and the specified activation function
/// to calculate the Z and A of the current layer.
/// </summary>
/// <param name="previousLayersActivations">Vector of the previous layer's activations.</param>
/// <param name="weights">Matrix of the current layers weights.</param>
/// <param name="bias">Vector of the current layers bias'.</param>
/// <param name="activation">The type of activation function to use.</param>
/// <returns>
/// It returns a tuple with the cache as the first item and the final activations as
/// the second item.
/// </returns>
private Tuple <LinearCache, MatrixVectors, MatrixVectors> ActivationsForward(MatrixVectors previousLayersActivations, MatrixVectors weights, MatrixVectors bias, Activation activation)
{
Tuple <LinearCache, MatrixVectors> cache = LinearForward(previousLayersActivations, weights, bias);
MatrixVectors z = cache.Item2;
MatrixVectors activationsVector;
switch (activation)
{
case Activation.Sigmoid:
activationsVector = Sigmoid(z);
break;
case Activation.ReLu:
activationsVector = Relu(z);
break;
default:
throw new ArgumentOutOfRangeException();
}
LinearCache linearCache = cache.Item1;
return(new Tuple <LinearCache, MatrixVectors, MatrixVectors>(linearCache, z, activationsVector));
}