/// <summary>
/// Calculate the loss/error of the output nodes.
/// </summary>
/// <param name="layer">the output layer</param>
/// <returns>a vector containing the errors</returns>
public static Vector OutputLoss(Layer layer, Vector desired, LossFunction f)
{
return(new Vector(VectorMath.ElementWiseOperation(layer.Nodes.Values, desired.Values, (a, b) => f(a, b))));
}