// Copyright (C) 2003 Ronan Collobert (collober@idiap.ch)
//                
// This file is part of Torch 3.
//
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
// 3. The name of the author may not be used to endorse or promote products
//    derived from this software without specific prior written permission.
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#ifndef SOFT_MAX_INC
#define SOFT_MAX_INC

#include "GradientMachine.h"

namespace Torch {

/** SoftMax layer for #GradientMachine#.

    The number of inputs/outputs is the number
    of units in the machine.

    Formally speaking, $ouputs[i] = 1/a * exp(inputs[i]-shift)$
    where $a = \sum_j exp(inputs[j]-shift)$.

    Options:
    \begin{tabular}{lcll}
      "shift"           & real &   shift to avoid overflow         & [0]\\
      "compute shift"   & bool &   compute shift to avoid overflow & [false]
    \end{tabular}

    (you can have the "shift" you want, if you want, or
    you can automatically compute the shift)

    @author Ronan Collobert (collober@idiap.ch)
*/
class SoftMax : public GradientMachine
{
  public:
    real shift;
    bool calc_shift;

    //-----

    /// Create a layer with #n_units# units.
    SoftMax(int n_units);

    //-----

    virtual void frameForward(int t, real *f_inputs, real *f_outputs);
    virtual void frameBackward(int t, real *f_inputs, real *beta_, real *f_outputs, real *alpha_);

    virtual ~SoftMax();
};

}

#endif