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 "lib/common.h"
00012 #include "kernel/Chi2Kernel.h"
00013 #include "features/Features.h"
00014 #include "features/SimpleFeatures.h"
00015 #include "lib/io.h"
00016 
00017 using namespace shogun;
00018 
00019 CChi2Kernel::CChi2Kernel(int32_t size, float64_t w)
00020 : CSimpleKernel<float64_t>(size), width(w)
00021 {
00022 }
00023 
00024 CChi2Kernel::CChi2Kernel(
00025     CSimpleFeatures<float64_t>* l, CSimpleFeatures<float64_t>* r, float64_t w, int32_t size)
00026 : CSimpleKernel<float64_t>(size), width(w)
00027 {
00028     init(l,r);
00029 }
00030 
00031 CChi2Kernel::~CChi2Kernel()
00032 {
00033     cleanup();
00034 }
00035 
00036 bool CChi2Kernel::init(CFeatures* l, CFeatures* r)
00037 {
00038     bool result=CSimpleKernel<float64_t>::init(l,r);
00039     init_normalizer();
00040     return result;
00041 }
00042 
00043 float64_t CChi2Kernel::compute(int32_t idx_a, int32_t idx_b)
00044 {
00045     int32_t alen, blen;
00046     bool afree, bfree;
00047 
00048     float64_t* avec=
00049         ((CSimpleFeatures<float64_t>*) lhs)->get_feature_vector(idx_a, alen, afree);
00050     float64_t* bvec=
00051         ((CSimpleFeatures<float64_t>*) rhs)->get_feature_vector(idx_b, blen, bfree);
00052     ASSERT(alen==blen);
00053 
00054     float64_t result=0;
00055     for (int32_t i=0; i<alen; i++)
00056     {
00057         float64_t n=avec[i]-bvec[i];
00058         float64_t d=avec[i]+bvec[i];
00059         if (d!=0)
00060             result+=n*n/d;
00061     }
00062 
00063     result=exp(-result/width);
00064 
00065     ((CSimpleFeatures<float64_t>*) lhs)->free_feature_vector(avec, idx_a, afree);
00066     ((CSimpleFeatures<float64_t>*) rhs)->free_feature_vector(bvec, idx_b, bfree);
00067 
00068     return result;
00069 }

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