Chi2Kernel.cpp

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00001 /*
00002  * This program is free software; you can redistribute it and/or modify
00003  * it under the terms of the GNU General Public License as published by
00004  * the Free Software Foundation; either version 3 of the License, or
00005  * (at your option) any later version.
00006  *
00007  * Written (W) 1999-2009 Soeren Sonnenburg
00008  * Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
00009  */
00010 
00011 #include <shogun/lib/common.h>
00012 #include <shogun/kernel/Chi2Kernel.h>
00013 #include <shogun/features/Features.h>
00014 #include <shogun/io/SGIO.h>
00015 
00016 using namespace shogun;
00017 
00018 void
00019 CChi2Kernel::init()
00020 {
00021     SG_ADD(&width, "width", "Kernel width.", MS_AVAILABLE);
00022 }
00023 
00024 CChi2Kernel::CChi2Kernel()
00025 : CDotKernel(0), width(0)
00026 {
00027     init();
00028 }
00029 
00030 CChi2Kernel::CChi2Kernel(int32_t size, float64_t w)
00031 : CDotKernel(size), width(w)
00032 {
00033     init();
00034 }
00035 
00036 CChi2Kernel::CChi2Kernel(
00037     CDenseFeatures<float64_t>* l, CDenseFeatures<float64_t>* r, float64_t w, int32_t size)
00038 : CDotKernel(size), width(w)
00039 {
00040     init();
00041     init(l,r);
00042 }
00043 
00044 CChi2Kernel::~CChi2Kernel()
00045 {
00046     cleanup();
00047 }
00048 
00049 bool CChi2Kernel::init(CFeatures* l, CFeatures* r)
00050 {
00051     bool result=CDotKernel::init(l,r);
00052     init_normalizer();
00053     return result;
00054 }
00055 
00056 float64_t CChi2Kernel::compute(int32_t idx_a, int32_t idx_b)
00057 {
00058     int32_t alen, blen;
00059     bool afree, bfree;
00060 
00061     float64_t* avec=
00062         ((CDenseFeatures<float64_t>*) lhs)->get_feature_vector(idx_a, alen, afree);
00063     float64_t* bvec=
00064         ((CDenseFeatures<float64_t>*) rhs)->get_feature_vector(idx_b, blen, bfree);
00065     ASSERT(alen==blen);
00066 
00067     float64_t result=0;
00068     for (int32_t i=0; i<alen; i++)
00069     {
00070         float64_t n=avec[i]-bvec[i];
00071         float64_t d=avec[i]+bvec[i];
00072         if (d!=0)
00073             result+=n*n/d;
00074     }
00075 
00076     result=exp(-result/width);
00077 
00078     ((CDenseFeatures<float64_t>*) lhs)->free_feature_vector(avec, idx_a, afree);
00079     ((CDenseFeatures<float64_t>*) rhs)->free_feature_vector(bvec, idx_b, bfree);
00080 
00081     return result;
00082 }
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