fn_fldr.hpp

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// Copyright (C) 2011 the authors listed below
// http://ecocpak.sourceforge.net
// 
// Authors:
// - Dimitrios Bouzas (bouzas at ieee dot org)
// - Nikolaos Arvanitopoulos (niarvani at ieee dot org)
// - Anastasios Tefas (tefas at aiia dot csd dot auth dot gr)
// 
// This file is part of the ECOC PAK C++ library. It is 
// provided without any warranty of fitness for any purpose.
//
// You can redistribute this file and/or modify it under 
// the terms of the GNU Lesser General Public License (LGPL) 
// as published by the Free Software Foundation, either 
// version 3 of the License or (at your option) any later 
// version.
// (see http://www.opensource.org/licenses for more info)





template<typename T1>
typename T1::elem_type
fldr
  (
  const Base<typename T1::elem_type, T1>& X, 
  const Base<typename T1::elem_type, T1>& Y
  )
  {
  arma_extra_debug_sigprint();
  
  // alias to element type
  typedef typename T1::elem_type eT;
  
  // unwrap first samples matrix
  const unwrap<T1>              tmp_X(X.get_ref());
  const   Mat<eT>& samples_X =  tmp_X.M;
  
  // unwrap second samples matrix
  const unwrap<T1>             tmp_Y(Y.get_ref());
  const   Mat<eT>& samples_Y = tmp_Y.M;
  
  // check wether one of the input matrices or both are empty
  if(samples_Y.is_empty() == true || samples_X.is_empty() == true)
    {
    return eT(0);
    }
   
  // compute "trace" of within-class scatter matrix
  eT trSw = accu(var(samples_X) + var(samples_Y));

  // compute the means of each column of the two data matrices
  Row<eT> tmp = mean(samples_X) - mean(samples_Y);

  // compute the trace of the between-class scatter matrix
  eT trSb = trace(trans(tmp) * tmp);
  
  // return the ratio of the traces
  return eT(trSb) / eT(trSw);
  }