PLearn 0.1
DilogarithmVariable.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: DilogarithmVariable.cc 3994 2005-08-25 13:35:03Z chapados $
00040  * This file is part of the PLearn library.
00041  ******************************************************* */
00042 
00043 #include "DilogarithmVariable.h"
00044 
00045 namespace PLearn {
00046 using namespace std;
00047 
00048 
00051 PLEARN_IMPLEMENT_OBJECT(DilogarithmVariable, 
00052                         "This Var computes the dilogarithm function", 
00053                         "The dilogarithm function is useful to compute the primitive of the softplus.\n"
00054                         "  dilogarithm(x) = sum_{k=1}^\\infty x^k/k^2\n"
00055                         "so dilogarithm'(x) = -(1/x)log(1-x), i.e. e^x dilogarithm'(-e^x)=log(1+e^x)=softplus(x)\n"
00056                         "and primitive(softplus)(x) = -dilogarithm(-e^x)\n");
00057 
00058 DilogarithmVariable::DilogarithmVariable(Variable* input) 
00059     : inherited(input, input->length(), input->width())
00060 {}
00061 
00062 
00063 void DilogarithmVariable::recomputeSize(int& l, int& w) const
00064 {
00065     if (input) {
00066         l = input->length();
00067         w = input->width();
00068     } else
00069         l = w = 0;
00070 }
00071 
00072 void DilogarithmVariable::fprop()
00073 {
00074     for(int i=0; i<nelems(); i++)
00075     {
00076         valuedata[i] = dilogarithm(input->valuedata[i]);
00077 #ifdef BOUNDCHECK
00078         if (is_missing(valuedata[i]))
00079             PLWARNING("dilogarithm returned NaN");
00080 #endif
00081     }
00082 }
00083 
00084 
00085 void DilogarithmVariable::bprop()
00086 {
00087     for(int i=0; i<nelems(); i++)
00088     {
00089         real xi = input->valuedata[i];
00090         if (xi!=0)
00091             input->gradientdata[i] -= gradientdata[i] * log1p(-xi)/xi;
00092     }
00093 }
00094 
00095 
00096 void DilogarithmVariable::symbolicBprop()
00097 {
00098     PLERROR("DilogarithmVariable::symbolicBprop() not implemented");
00099 }
00100 
00101 } // end of namespace PLearn
00102 
00103 
00104 /*
00105   Local Variables:
00106   mode:c++
00107   c-basic-offset:4
00108   c-file-style:"stroustrup"
00109   c-file-offsets:((innamespace . 0)(inline-open . 0))
00110   indent-tabs-mode:nil
00111   fill-column:79
00112   End:
00113 */
00114 // vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=79 :
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