PLearn 0.1
MarginPerceptronCostVariable.cc
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00001 // -*- C++ -*-
00002 
00003 // PLearn (A C++ Machine Learning Library)
00004 // Copyright (C) 1998 Pascal Vincent
00005 // Copyright (C) 1999-2002 Pascal Vincent, Yoshua Bengio, Rejean Ducharme and University of Montreal
00006 // Copyright (C) 2001-2002 Nicolas Chapados, Ichiro Takeuchi, Jean-Sebastien Senecal
00007 // Copyright (C) 2002 Xiangdong Wang, Christian Dorion
00008 // Copyright (C) 2003 Olivier Delalleau
00009 
00010 // Redistribution and use in source and binary forms, with or without
00011 // modification, are permitted provided that the following conditions are met:
00012 // 
00013 //  1. Redistributions of source code must retain the above copyright
00014 //     notice, this list of conditions and the following disclaimer.
00015 // 
00016 //  2. Redistributions in binary form must reproduce the above copyright
00017 //     notice, this list of conditions and the following disclaimer in the
00018 //     documentation and/or other materials provided with the distribution.
00019 // 
00020 //  3. The name of the authors may not be used to endorse or promote
00021 //     products derived from this software without specific prior written
00022 //     permission.
00023 // 
00024 // THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
00025 // IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
00026 // OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
00027 // NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
00028 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
00029 // TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
00030 // PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
00031 // LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00032 // NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00033 // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00034 // 
00035 // This file is part of the PLearn library. For more information on the PLearn
00036 // library, go to the PLearn Web site at www.plearn.org
00037 
00038 
00039 /* *******************************************************      
00040  * $Id: MarginPerceptronCostVariable.cc 3994 2005-08-25 13:35:03Z chapados $
00041  * This file is part of the PLearn library.
00042  ******************************************************* */
00043 
00044 #include "MarginPerceptronCostVariable.h"
00045 
00046 namespace PLearn {
00047 using namespace std;
00048 
00051 PLEARN_IMPLEMENT_OBJECT(
00052     MarginPerceptronCostVariable,
00053     "Compute sigmoid of its first input, and then computes the negative "
00054     "cross-entropy cost",
00055     "NO HELP");
00056 
00058 // MarginPerceptronCostVariable //
00060 
00061 MarginPerceptronCostVariable::MarginPerceptronCostVariable()
00062     : margin(0.)
00063 { }
00064   
00065 MarginPerceptronCostVariable::MarginPerceptronCostVariable(Variable* output, Variable* target, real m)
00066     : inherited(output,target,1,1),margin(m)
00067 {
00068     build_();
00069 }
00070 
00071 void
00072 MarginPerceptronCostVariable::build()
00073 {
00074     inherited::build();
00075     build_();
00076 }
00077 
00078 void
00079 MarginPerceptronCostVariable::build_()
00080 {
00081     // input2 is target from constructor
00082     if (input2 && input2->size() != 1)
00083         PLERROR("In MarginPerceptronCostVariable: target represents a class (0...n_classes-1) and must be a single integer");
00084 }
00085 
00086 void
00087 MarginPerceptronCostVariable::declareOptions(OptionList &ol)
00088 {
00089     declareOption(ol, "margin", &MarginPerceptronCostVariable::margin, OptionBase::buildoption, "");
00090     inherited::declareOptions(ol);
00091 }
00092 
00094 // recomputeSize //
00096 void MarginPerceptronCostVariable::recomputeSize(int& l, int& w) const
00097 { l=1, w=1; }
00098 
00100 // fprop //
00102 void MarginPerceptronCostVariable::fprop()
00103 {
00104     real cost = 0.0;
00105     int target = int(input2->valuedata[0]);
00106     for (int i=0; i<input1->size(); i++)
00107     {
00108         real output = input1->valuedata[i];
00109         int signed_target = input1->size()==1?target*2-1:(target==i) - (target!=i);
00110         real diff = margin - signed_target * output;
00111         if (diff>0)
00112             cost += diff;
00113     }
00114     valuedata[0] = cost;
00115 }
00116 
00118 // bprop //
00120 void MarginPerceptronCostVariable::bprop()
00121 {
00122     real gr = *gradientdata;
00123     int target = int(input2->valuedata[0]);
00124     for (int i=0; i<input1->size(); i++)
00125     {
00126         real output = input1->valuedata[i];
00127         int signed_target = input1->size()==1?target*2-1:(target==i) - (target!=i);
00128         real diff = margin - signed_target * output;
00129         if (diff>0)
00130             input1->gradientdata[i] -= gr*signed_target;
00131     }
00132 }
00133 
00134 } // end of namespace PLearn
00135 
00136 
00137 /*
00138   Local Variables:
00139   mode:c++
00140   c-basic-offset:4
00141   c-file-style:"stroustrup"
00142   c-file-offsets:((innamespace . 0)(inline-open . 0))
00143   indent-tabs-mode:nil
00144   fill-column:79
00145   End:
00146 */
00147 // vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=79 :
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