/// <summary>
/// Computes the error signal of the layer, also gradients if applicable
/// </summary>
/// <param name="input">Previous layer's values</param>
/// <param name="output">Whether the layer is the output layer</param>
/// <param name="loss">The loss of the layer</param>
/// <param name="calcgradients">Whether or not to calculate gradients in the layer</param>
public void Backprop(List <double[]> inputs, Layer outputlayer, double loss, bool calcgradients)
{
//Reset errors
Errors = new List <double[]>();
//Calculate errors
if (outputlayer is null)
{
for (int j = 0; j < inputs.Count; j++)
{
Errors.Add(new double[Length]);
for (int i = 0; i < Length; i++)
{
//(i == loss ? 1d : 0d)
Errors[j][i] = 2d * (Values[j][i] - loss);
}
}
}
else
{
for (int i = 0; i < inputs.Count; i++)
{
Errors.Add(new double[outputlayer.InputLength]);
}
if (outputlayer is SumLayer)
{
//Errors with respect to the output of the convolution
//dl/do
for (int i = 0; i < outputlayer.ZVals.Count; i++)
{
for (int k = 0; k < outputlayer.Length; k++)
{
for (int j = 0; j < outputlayer.InputLength; j++)
{
Errors[i][j] += outputlayer.Errors[i][k];
}
}
}
}
//Apply tanhderriv, if applicable, to the output's zvals
var outputZVals = outputlayer.ZVals;
if (outputlayer.ActivationFunction == 0)
{
outputZVals = Maths.TanhDerriv(outputlayer.ZVals);
}
if (outputlayer.ActivationFunction == 1)
{
outputZVals = Maths.ReLuDerriv(outputlayer.ZVals);
}
if (outputlayer is FullyConnectedLayer)
{
var FCLOutput = outputlayer as FullyConnectedLayer;
for (int i = 0; i < outputlayer.ZVals.Count; i++)
{
for (int k = 0; k < FCLOutput.Length; k++)
{
for (int j = 0; j < FCLOutput.InputLength; j++)
{
Errors[i][j] += FCLOutput.Weights[k, j] * outputZVals[i][k] * FCLOutput.Errors[i][k];
}
}
}
}
if (outputlayer is ConvolutionLayer)
{
var CLOutput = outputlayer as ConvolutionLayer;
for (int i = 0; i < outputlayer.ZVals.Count; i++)
{
if ((outputlayer as ConvolutionLayer).DownOrUp)
{
Errors[i] = Maths.Convert(CLOutput.UnPad(CLOutput.FullConvolve(CLOutput.Weights, Maths.Convert(CLOutput.Errors[i]))));
}
else
{
Errors[i] = Maths.Convert(CLOutput.UnPad(CLOutput.Convolve(CLOutput.Weights, Maths.Convert(CLOutput.Errors[i]))));
}
}
//Errors = Maths.Convert(CLOutput.UnPad(CLOutput.FullConvolve(CLOutput.Weights, Maths.Convert(CLOutput.Errors))));
}
if (outputlayer is PoolingLayer)
{
var PLOutput = outputlayer as PoolingLayer;
for (int b = 0; b < NN.BatchSize; b++)
{
if (PLOutput.DownOrUp)
{
int iterator = 0;
var wets = Maths.Convert(PLOutput.Weights);
for (int i = 0; i < Length; i++)
{
if (wets[i] == 0)
{
continue;
}
Errors[b][i] = PLOutput.Errors[b][iterator];
iterator++;
}
}
else
{
//Sum the errors
double[,] outputerrors = Maths.Convert(PLOutput.Errors[b]);
int oel = outputerrors.GetLength(0);
int oew = outputerrors.GetLength(1);
double[,] errors = new double[oel / PLOutput.PoolSize, oew / PLOutput.PoolSize];
for (int i = 0; i < oel; i++)
{
for (int ii = 0; ii < oew; ii++)
{
errors[i / PLOutput.PoolSize, ii / PLOutput.PoolSize] += outputerrors[i, ii];
}
}
Errors[b] = Maths.Convert(errors);
}
}
}
}
//Normalize errors (if applicable)
if (NN.NormErrors && Errors[0].Length > 1)
{
Errors = Maths.Normalize(Errors);
}
if (calcgradients)
{
if (this is FullyConnectedLayer)
{
(this as FullyConnectedLayer).CalcGradients(inputs, outputlayer);
}
if (this is ConvolutionLayer)
{
(this as ConvolutionLayer).CalcGradients(inputs, outputlayer);
}
if (this is PoolingLayer)
{
return;
}
if (this is SumLayer)
{
return;
}
}
}
public abstract void CalcGradients(List <double[]> inputs, Layer outputlayer);