#ifndef _CUUPDATABLE_BIAS_H_
#define _CUUPDATABLE_BIAS_H_


#include "cuComponent.h"
#include "cumatrix.h"


#include "Matrix.h"
#include "Vector.h"


namespace TNet {
  /**
   * \brief CuUpdatableBias summation function
   *
   * \ingroup CuNNUpdatable
   * Implements forward pass: \f[ Y_i=X_i +{\beta}_i \f]
   * Error propagation: \f[ E_i = e_i \f]
   *
   * Weight adjust:
   * for bias: \f[ {\Beta}_i = {\beta}_i - \alpha(1-\mu)e_i - \mu \Delta \f]
   * where
   *  - D for weight decay => penalizing large weight
   *  - \f$ \alpha \f$ for learning rate
   *  - \f$ \mu \f$ for momentum => avoiding oscillation
   */
  class CuUpdatableBias : public CuUpdatableComponent
  {
    public:

      CuUpdatableBias(size_t nInputs, size_t nOutputs, CuComponent *pPred); 
      ~CuUpdatableBias();  
      
      ComponentType GetType() const;
      const char* GetName() const;
      
      const CuMatrix<float>& GetErrorOutput();

      void PropagateFnc(const CuMatrix<BaseFloat>& X, CuMatrix<BaseFloat>& Y);
      void BackpropagateFnc(const CuMatrix<BaseFloat>& X, CuMatrix<BaseFloat>& Y);

      void Update();

      void ReadFromStream(std::istream& rIn);
      void WriteToStream(std::ostream& rOut);
      
      void Backpropagate();

    protected:
      CuVector<BaseFloat> mBias;       ///< Vector with biases

      CuVector<BaseFloat> mBiasCorrection;      ///< Vector for bias updates

  };




  ////////////////////////////////////////////////////////////////////////////
  // INLINE FUNCTIONS 
  // CuUpdatableBias::
  inline 
  CuUpdatableBias::
  CuUpdatableBias(size_t nInputs, size_t nOutputs, CuComponent *pPred)
    : CuUpdatableComponent(nInputs, nOutputs, pPred), 
      mBias(nOutputs), mBiasCorrection(nOutputs)
  { 
    mBiasCorrection.SetConst(0.0);
  }


  inline
  CuUpdatableBias::
  ~CuUpdatableBias()
  { }

  inline CuComponent::ComponentType
  CuUpdatableBias::
  GetType() const
  {
    return CuComponent::UPDATABLEBIAS;
  }

  inline const char*
  CuUpdatableBias::
  GetName() const
  {
    return "<updatablebias>";
  }
 
  inline void
  CuUpdatableBias::
  Backpropagate()
  {
  }

  inline const CuMatrix<BaseFloat>&
  CuUpdatableBias::
  GetErrorOutput()
  {
    return GetErrorInput();
  }

} //namespace



#endif