Program Listing for File gram_savitzky_golay.hpp

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// BSD 2-Clause License
//
// Copyright (c) 2012-2019, CNRS-UM LIRMM, CNRS-AIST JRL
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// reference: https://github.com/arntanguy/gram_savitzky_golay
//
// Modified in 2021 by Neuro-Electronics Research Flanders
//
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#pragma once

#include <vector>
#include <cassert>
#include <cmath>

namespace gram_sg
{

inline double compute_gram_polynomial(const int i, const int m, const int k, const int s){
    if(k>0)
    {
        return (4.*k-2.) / (k*(2.*m - k+1.)) * (i * compute_gram_polynomial(i, m, k - 1, s) + s * compute_gram_polynomial(i, m, k-1, s-1))
                - ((k-1.) * (2.*m + k)) / (k * (2.*m - k+1.)) * compute_gram_polynomial(i, m, k-2, s);
    }

    if(k == 0 && s == 0){
        return 1.;
    }else{
        return 0.;
    }

};


inline double compute_generalized_factorial(const int a, const int b){
    double gf = 1.;

    for(int j=(a-b)+1; j<=a; j++)
    {
        gf*=j;
    }
    return gf;
};


inline double compute_weight(const int i, const int t, const int m, const int n, const int s){
    double w = 0;
    for(int k = 0; k <= n; ++k)
    {
        w = w + (2*k+1) * (compute_generalized_factorial(2*m, k)/compute_generalized_factorial(2*m+k+1, k+1))
                * compute_gram_polynomial(i, m, k, 0)* compute_gram_polynomial(t, m, k, s);
    }
    return w;
};


inline std::vector<double> compute_weights(const int m, const int t, const int n, const int s){
    std::vector<double> weights(2*static_cast<size_t>(m)+1);

    for(int i=0; i<2*m+1; ++i)
    {
        weights[static_cast<size_t>(i)] = compute_weight(i - m, t, m, n, s);
    }
    return weights;
};
} // namespace gram_sg