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exit.cpp
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1
29#include <itpp/comm/exit.h>
30#include <itpp/stat/histogram.h> //histogram class for mutual information computation
31#include <itpp/base/itcompat.h>
32
33namespace itpp
34{
35double EXIT::Gaussian_Fct::operator()(double x) const
36{
37 return (1.0/std::sqrt(_sigma*itpp::m_2pi))*std::exp(-itpp::sqr(x-(_sigma/2.0))/(2.0*_sigma))*::log2(1+std::exp(-x));
38}
39
40double EXIT::extrinsic_mutual_info(const itpp::vec &obs, const itpp::bvec &cond, const int &N)
41{
42 //initialize histogram
43 itpp::Histogram<double> hist(itpp::min(obs), itpp::max(obs), N);//common definition interval for both PDFs
44
45 //conditional PDF knowing that a bit of 0 was emitted
46 itpp::ivec idx = itpp::find(cond==itpp::bin(0));
47 itpp::vec cond_obs = obs(idx);
48 hist.reset();//start counting
49 hist.update(cond_obs);
50 itpp::vec left_pdf = hist.get_pdf();//the pdf is computed without taking into account the interval length (step)
51 itpp::ivec left_int = itpp::find(left_pdf!=0);//integration interval for the left PDF
52
53 //conditional PDF knowing that a bit of 1 was emitted
54 idx = itpp::find(cond==itpp::bin(1));
55 cond_obs = obs(idx);
56 hist.reset();//restart counting
57 hist.update(cond_obs);
58 itpp::vec right_pdf = hist.get_pdf();
59 itpp::ivec right_int = itpp::find(right_pdf!=0);//integration interval for the right PDF
60
61 //mutual extrinsic information
62 itpp::vec left_half = itpp::elem_mult(left_pdf(left_int), itpp::log2(itpp::elem_div(2.0*left_pdf(left_int), left_pdf(left_int)+right_pdf(left_int))));
63 double IE = itpp::sum(left_half)-0.5*(left_half(0)+left_half(left_half.length()-1));//numerical integration without taking into account the inteval length (see conditional PDF computation)
64 itpp::vec right_half = itpp::elem_mult(right_pdf(right_int), itpp::log2(itpp::elem_div(2.0*right_pdf(right_int), left_pdf(right_int)+right_pdf(right_int))));
65 IE += itpp::sum(right_half)-0.5*(right_half(0)+right_half(right_half.length()-1));//numerical integration
66 IE *= 0.5;
67
68 return IE;
69}
70
71}//namespace itpp
72
double extrinsic_mutual_info(const itpp::vec &obs, const itpp::bvec &cond, const int &N=100)
Computes the extrinsic mutual information.
Definition: exit.cpp:40
Histogram computation class.
Definition: histogram.h:76
void reset()
Bins reset, so accumulation can be restarted.
Definition: histogram.h:95
Binary arithmetic (boolean) class.
Definition: binary.h:57
Definitions for EXtrinsic Information Transfer (EXIT) chart class.
vec get_pdf() const
Experimental Probability Density Function (PDF) computation.
Definition: histogram.h:201
void update(Num_T value)
Histogram update.
Definition: histogram.h:164
vec log2(const vec &x)
log-2 of the elements
Definition: log_exp.cpp:36
vec exp(const vec &x)
Exp of the elements of a vector x.
Definition: log_exp.h:155
T sum(const Vec< T > &v)
Sum of all elements in the vector.
Definition: matfunc.h:59
T min(const Vec< T > &in)
Minimum value of vector.
Definition: min_max.h:125
T max(const Vec< T > &v)
Maximum value of vector.
Definition: min_max.h:45
ivec find(const bvec &invector)
Return a integer vector with indicies where bvec == 1.
Definition: specmat.cpp:40
vec sqr(const cvec &data)
Absolute square of elements.
Definition: elem_math.cpp:36
vec sqrt(const vec &x)
Square root of the elements.
Definition: elem_math.h:123
Histogram class - header file.
IT++ compatibility types and functions.
itpp namespace
Definition: itmex.h:37
const double m_2pi
Constant 2*Pi.
Definition: misc.h:106
Mat< Num_T > elem_div(const Mat< Num_T > &m1, const Mat< Num_T > &m2)
Element wise division of two matrices.
Definition: mat.h:1688
Mat< Num_T > elem_mult(const Mat< Num_T > &m1, const Mat< Num_T > &m2)
Element wise multiplication of two matrices.
Definition: mat.h:1582
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