Neuron.cs

public class Neuron : INeuron
{
    private IActivationFunction _activationFunction;
    private IInputFunction _inputFunction;

    /// <summary>
    /// Input connections of the neuron.
    /// </summary>
    public List<ISynapse> Inputs { get; set; }

    /// <summary>
    /// Output connections of the neuron.
    /// </summary>
    public List<ISynapse> Outputs { get; set; }

    public Guid Id { get; private set; }

    /// <summary>
    /// Calculated partial derivate in previous iteration of training process.
    /// </summary>
    public double PreviousPartialDerivate { get; set; }

    public Neuron(IActivationFunction activationFunction, IInputFunction inputFunction)
    {
        Id = Guid.NewGuid();
        Inputs = new List<ISynapse>();
        Outputs = new List<ISynapse>();

        _activationFunction = activationFunction;
        _inputFunction = inputFunction;
    }

    /// <summary>
    /// Connect two neurons. 
    /// This neuron is the output neuron of the connection.
    /// </summary>
    /// <param name="inputNeuron">Neuron that will be input neuron of the newly created connection.</param>
    public void AddInputNeuron(INeuron inputNeuron)
    {
        var synapse = new Synapse(inputNeuron, this);
        Inputs.Add(synapse);
        inputNeuron.Outputs.Add(synapse);
    }

    /// <summary>
    /// Connect two neurons. 
    /// This neuron is the input neuron of the connection.
    /// </summary>
    /// <param name="outputNeuron">Neuron that will be output neuron of the newly created connection.</param>
    public void AddOutputNeuron(INeuron outputNeuron)
    {
        var synapse = new Synapse(this, outputNeuron);
        Outputs.Add(synapse);
        outputNeuron.Inputs.Add(synapse);
    }

    /// <summary>
    /// Calculate output value of the neuron.
    /// </summary>
    /// <returns>
    /// Output of the neuron.
    /// </returns>
    public double CalculateOutput()
    {
        return _activationFunction.CalculateOutput(_inputFunction.CalculateInput(this.Inputs));
    }

    /// <summary>
    /// Input Layer neurons just receive input values.
    /// For this they need to have connections.
    /// This function adds this kind of connection to the neuron.
    /// </summary>
    /// <param name="inputValue">
    /// Initial value that will be "pushed" as an input to connection.
    /// </param>
    public void AddInputSynapse(double inputValue)
    {
        var inputSynapse = new InputSynapse(this, inputValue);
        Inputs.Add(inputSynapse);
    }

    /// <summary>
    /// Sets new value on the input connections.
    /// </summary>
    /// <param name="inputValue">
    /// New value that will be "pushed" as an input to connection.
    /// </param>
    public void PushValueOnInput(double inputValue)
    {
        ((InputSynapse)Inputs.First()).Output = inputValue;
    }
}