ChebyshevU.cpp

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 * work.  Good starting points are:
 *
 * [1] Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).
 * [2] Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).
 * [3] Sun, Lin & Gezelter, J. Chem. Phys. 128, 234107 (2008).
 * [4] Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
 * [5] Kuang & Gezelter, Mol. Phys., 110, 691-701 (2012).
 * [6] Lamichhane, Gezelter & Newman, J. Chem. Phys. 141, 134109 (2014).
 * [7] Lamichhane, Newman & Gezelter, J. Chem. Phys. 141, 134110 (2014).
 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 */
 
#include "math/ChebyshevU.hpp"
 
namespace OpenMD {
  ChebyshevU::ChebyshevU(int maxPower) : maxPower_(maxPower) {
    assert(maxPower >= 0);
    GeneratePolynomials(maxPower_);
  }
 
  void ChebyshevU::GeneratePolynomials(int maxPower) {
    GenerateFirstTwoTerms();
 
    DoublePolynomial twoX;
    twoX.setCoefficient(1, 2.0);
 
    // recursive generate the high order term of Chebyshev Polynomials
    // Cn+1(x) = Cn(x) * 2x - Cn-1(x)
    for (int i = 2; i <= maxPower; ++i) {
      DoublePolynomial cn;
 
      cn = polyList_[i - 1] * twoX - polyList_[i - 2];
      polyList_.push_back(cn);
    }
  }
 
  void ChebyshevU::GenerateFirstTwoTerms() {
    DoublePolynomial u0;
    u0.setCoefficient(0, 1.0);
    polyList_.push_back(u0);
 
    DoublePolynomial u1;
    u1.setCoefficient(1, 2.0);
    polyList_.push_back(u1);
  }
 
}  // namespace OpenMD