PLearn 0.1
CrossEntropyVariable.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 
00009 // Redistribution and use in source and binary forms, with or without
00010 // modification, are permitted provided that the following conditions are met:
00011 // 
00012 //  1. Redistributions of source code must retain the above copyright
00013 //     notice, this list of conditions and the following disclaimer.
00014 // 
00015 //  2. Redistributions in binary form must reproduce the above copyright
00016 //     notice, this list of conditions and the following disclaimer in the
00017 //     documentation and/or other materials provided with the distribution.
00018 // 
00019 //  3. The name of the authors may not be used to endorse or promote
00020 //     products derived from this software without specific prior written
00021 //     permission.
00022 // 
00023 // THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
00024 // IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
00025 // OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
00026 // NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
00027 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
00028 // TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
00029 // PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
00030 // LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00031 // NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00032 // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00033 // 
00034 // This file is part of the PLearn library. For more information on the PLearn
00035 // library, go to the PLearn Web site at www.plearn.org
00036 
00037 
00038 /* *******************************************************      
00039  * $Id: CrossEntropyVariable.cc 6351 2006-10-25 19:05:45Z chapados $
00040  * This file is part of the PLearn library.
00041  ******************************************************* */
00042 
00043 #include "CrossEntropyVariable.h"
00044 
00045 namespace PLearn {
00046 using namespace std;
00047 
00048 
00049 
00052 PLEARN_IMPLEMENT_OBJECT(CrossEntropyVariable,
00053                         "cost = - sum_i {target_i * log(output_i) + (1-target_i) * log(1-output_i)}",
00054                         "NO HELP");
00055 
00056 CrossEntropyVariable::CrossEntropyVariable(Variable* netout, Variable* target)
00057     : inherited(netout,target,1,1)
00058 {
00059     build_();
00060 }
00061 
00062 void
00063 CrossEntropyVariable::build()
00064 {
00065     inherited::build();
00066     build_();
00067 }
00068 
00069 void
00070 CrossEntropyVariable::build_()
00071 {
00072     // input1 and input2 are (respectively) netout and target from constructor
00073     if (input1 && input2 && (input1->size() != input2->size()))
00074         PLERROR("In CrossEntropyVariable: netout and target must have the same size");
00075 }
00076 
00077 
00078 void CrossEntropyVariable::recomputeSize(int& l, int& w) const
00079 { l=1, w=1; }
00080 
00081 void CrossEntropyVariable::fprop()
00082 {
00083     real cost = 0.0;
00084     for (int i=0; i<input1->size(); i++)
00085     {
00086         real output = input1->valuedata[i];
00087         real target = input2->valuedata[i];
00088         PLASSERT( fast_exact_is_equal(target, 0) ||
00089                 fast_exact_is_equal(target, 1)    );
00090         PLASSERT( output >= 0 && output <= 1 );
00091         if ((fast_exact_is_equal(output,0) && !fast_exact_is_equal(target,0))
00092          || (fast_exact_is_equal(output,1) && !fast_exact_is_equal(target,1)))
00093             PLERROR("CrossEntropyVariable::fprop: model output is either exactly "
00094                     "0.0 or 1.0; cannot compute cost function");
00095         if (!fast_exact_is_equal(output,0) && !fast_exact_is_equal(output,1)) {
00096             cost += target*pl_log(output) + (1.0-target)*pl_log(1.0-output);
00097         }
00098     }
00099     valuedata[0] = -cost;
00100 }
00101 
00102 void CrossEntropyVariable::bprop()
00103 {
00104     real gr = *gradientdata;
00105     for (int i=0; i<input1->size(); i++)
00106     {
00107         real output = input1->valuedata[i];
00108         real target = input2->valuedata[i];
00109 #ifdef BOUNDCHECK
00110         if (fast_exact_is_equal(output, target))
00111             PLERROR("CrossEntropyVariable::bprop: model output is either exactly "
00112                     "0.0 or 1.0; cannot compute bprop");
00113 #endif
00114         input1->gradientdata[i] += gr*(-target/output + (1.0-target)/(1.0-output));
00115     }
00116 }
00117 
00118 } // end of namespace PLearn
00119 
00120 
00121 /*
00122   Local Variables:
00123   mode:c++
00124   c-basic-offset:4
00125   c-file-style:"stroustrup"
00126   c-file-offsets:((innamespace . 0)(inline-open . 0))
00127   indent-tabs-mode:nil
00128   fill-column:79
00129   End:
00130 */
00131 // vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=79 :
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