arpls.cpp

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#include <cmath>
 
#include "../smoothing/whittaker.h"
 
#include "arpls.h"
 
namespace sablib {
 
//
// Implementation of BaselineArPLS() function
//
const std::vector<double> BaselineArPLS(
    std::vector<double> & y, const double lambda, const unsigned int s,
    const unsigned int loop, const double eps
)
{
    if(y.size() == 0) {
        throw std::invalid_argument("BaselineArPLS(): the length of y is zero.");
    }
 
    if(lambda <= 0) {
        throw std::invalid_argument("BaselineArPLS(): non-positive lambda value is given.");
    }
 
    if(s == 0 || s > 3) {
        throw std::invalid_argument("BaselineArPLS(): s must be 1, 2 or 3.");
    }
 
    if(loop == 0) {
        throw std::invalid_argument("BaselineArPLS(): loop is zero.");
    }
 
    if(eps <= 0) {
        throw std::invalid_argument("BaselineArPLS(): non-positive eps value is given.");
    }
 
    size_t m = y.size();
    Eigen::VectorXd yy, w, wt, z, d, tmp;
    Eigen::SparseMatrix<double> I, D, lambdaDTD;
    double mean, sd;
    Eigen::Index ct;
 
    auto logistic = [](const double xx) {
        if(xx < 0) {
            double t = std::exp(xx);
            return t / (t + 1);
        }
        else {
            return 1 / (1 + std::exp(-xx));
        }
    };
 
    yy = Eigen::VectorXd::Map(y.data(), m);
 
    w.setOnes(m);
 
    I.resize(m, m);
    I.setIdentity();
    D = Diff(I, s);
    lambdaDTD = lambda * (D.transpose() * D);
 
    for(unsigned int i = 0; i < loop; i++) {
        z = Whittaker(yy, w, lambdaDTD);
 
        d = yy - z;
 
        ct = (d.array() < 0).count();
        mean = (d.array() < 0).select(d, 0).sum() / ct;
        sd = std::sqrt((d.array() < 0).select((d.array() - mean).matrix(), 0).squaredNorm() / (ct - 1));
 
        tmp = (-2 * (d.array() + mean - 2 * sd) / sd).matrix().unaryExpr(logistic);
        wt = (d.array() >= 0).select(tmp, 1);
 
        if ((w - wt).norm() / w.norm() < eps) {
            break;
        }
 
        w = wt;
    }
 
    std::vector<double> result(z.size());
    Eigen::VectorXd::Map(result.data(), result.size()) = z;
 
    return result;
}
 
}; // namespace sablib