/// <summary>
/// </summary>
/// <param name="dz"></param>
/// <returns></returns>
public List <double> backward(List <double> dz)
{
List <double> dw = new List <double>();
List <double> dx = new List <double>();
double backward_signal = dz.Sum();
if (this.activation.Equals("sigmoid"))
{
backward_signal = this.activation_node.backward(backward_signal);
}
else
{
backward_signal = this.activation_node2.backward(backward_signal);
}
List <double> backWard = this.sumNode.backward(backward_signal);
for (int i = 0; i < this.multiplyNodes.Count; i++)
{
MultiplyNode mn = this.multiplyNodes[i];
List <double> retVals = mn.backward(backWard[i]);
dx.Add(retVals[0]);
dw.Add(retVals[1]);
}
//https://en.wikipedia.org/wiki/Gradient_descent
//df/dx1, df/dx2...
this.gradients.Add(dw);
return(dx);
}
/// <summary>
/// Greska se propagira u nazad kroz aktivacionu funkciju,
/// preko sabiraca, do svakog pojedinacnog mnozaca
/// </summary>
/// <param name="dz"></param>
/// <returns></returns>
public List <double> backward(List <double> dz)
{
//greska svakog ulaza
List <double> dw = new List <double>();
List <double> dx = new List <double>();
double backward_signal = dz.Sum();
//TODO 7: Izvrsiti propagaciju signala u nazad, prvo kroz aktivacionu funkciju,
// onda kroz sabirac pa kroz svaki pojedinacan mnozac
backward_signal = this.activation_node.backward(backward_signal);
//dobije se nazad lista gresaka po mnoziocima koje ulaze u sabirac
//z = x + y ===> dx = dz && dy = dz, te se dobije samo lista dz-ova onoliko puta koliko ima sabiraoca
List <double> sabiracListaGreska = this.sumNode.backward(backward_signal);
//za svaki sabiraoc (koji je ustv mnozac), izracunati gresku po promenljivoj i po tezini
for (int i = 0; i < sabiracListaGreska.Count; i++)
{
MultiplyNode mn = this.multiplyNodes[i];
List <double> parPromenljivaTezinaGreska = mn.backward(sabiracListaGreska[i]);
dx.Add(parPromenljivaTezinaGreska[0]);
dw.Add(parPromenljivaTezinaGreska[1]);
}
//https://en.wikipedia.org/wiki/Gradient_descent
//df/dx1, df/dx2...
this.gradients.Add(dw);
return(dx);
}