MethodSphere.cpp

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/*
 * MethodSphere.cpp
 *
 *  Created on: Nov 5, 2019
 *      Author: Nikhil
 */

#include <math.h>
#include <MethodSphere.h>
#include <iostream>
#include <limits>
#include "typedef.h"


MethodSphere::MethodSphere(double averagingDomainSize, std::string type="virial") : Method<MethodSphere>(averagingDomainSize)
{ 
    double normalizer;
    if (type =="hardy")
    {
        // weighting function:

        //w(r)= c if r<= R/2,
        //  = 2c(1-r/R) if R/2<=r<=R
        //where c= 8/(5\pi R^3)

        normalizer= 8/(5*M_PI*pow(averagingDomainSize,3));
        // constant polynomial
        std::deque<double> constant{normalizer};
        Polynomial constantPolynomial{constant};
        //linear polynomial
        std::deque<double> linear{2*normalizer,-2*normalizer/averagingDomainSize};
        Polynomial linearPolynomial{linear};


        // construct piecewise polynomial
        std::pair<double,double> interval;
        interval.first= 0;
        interval.second= averagingDomainSize/2;
        piecewisePolynomial[interval]= constantPolynomial;

        interval.first= averagingDomainSize/2;
        interval.second= averagingDomainSize;
        piecewisePolynomial[interval]= linearPolynomial;
        return;
    }
    else if (type == "virial")
    {
        normalizer= 1/(M_PI*pow(averagingDomainSize,3));
        std::deque<double> constant{normalizer};
        // constant polynomial
        Polynomial constantPolynomial{constant};

        std::pair<double,double> interval;
        interval.first= 0;
        interval.second= averagingDomainSize;
        piecewisePolynomial[interval]= constantPolynomial;
        return;
    }
    assert(0);
}

MethodSphere::MethodSphere(double averagingDomainSize, std::map<double,double> map) : Method<MethodSphere>(averagingDomainSize)
{ 
    // ensure the domain of map lies in between 0 and 1, and its range is non-negative
    assert(  (map.cbegin())->first >= 0  && 
             (map.cend())->first <= 1    &&
             (map.cbegin())->second >= 0 &&
             (map.cend())->second >= 0 );

    for (auto iter = map.cbegin(); iter != map.cend(); iter++)
    {
        // (y-y1)/(y2-y1) = (x-x1)/(x2-x1)
        // y = (y2-y1)/(x2-x1)  *  (x-x1)   +   y1
        //   = y1-x1*(y2-y1)/(x2-x1) + (y2-y1)/(x2-x1)  *   x
        auto nextiter= std::next(iter);
        if (nextiter != map.cend())
        {
            double x1= iter->first;  double x2= nextiter->first;
            x1= x1*averagingDomainSize; x2= x2*averagingDomainSize;
            std::pair<double,double> interval{x1,x2};

            double y1= iter->second; double y2= nextiter->second;
            std::deque<double> linear{ y1-x1*(y2-y1)/(x2-x1),  (y2-y1)/(x2-x1) };
            Polynomial linearPolynomial{linear};
            piecewisePolynomial[interval]= linearPolynomial;
        }
        else 
        {
            if (abs(iter->first-1.0)>epsilon)
                MY_ERROR("Weight function is not defined entirely on the averaging domain.");
            break;
        }
    }
    // now compute the normalizer 
    double integral= 0;
    for(auto iter=piecewisePolynomial.cbegin(); iter!=piecewisePolynomial.cend(); iter++)
    {
        Polynomial temp(iter->second);
        temp.coefficients.push_front(0); temp.coefficients.push_front(0); // Multiplying the polynomial by r^2
        Polynomial integratedPolynomial= temp.integrate();
        integral= integral+integratedPolynomial(iter->first.second) - integratedPolynomial(iter->first.first);
    }
    double normalizer = 1/(4*M_PI*integral);
    for(auto iter=piecewisePolynomial.begin(); iter!=piecewisePolynomial.end(); iter++)
    {
        for(auto& coeff : iter->second.coefficients)
        {
            coeff= normalizer*coeff;
        }
    }
}


MethodSphere::MethodSphere(const MethodSphere& _hardy) : Method<MethodSphere>(_hardy)
{
    *this= _hardy;
}

MethodSphere::~MethodSphere() {
    // TODO Auto-generated destructor stub
}

double MethodSphere::integratePolynomial(const int& degree,
                                   const double& a,
                                   const double& b,
                                   const double& r1,
                                   const double& r2) const
{
    assert(r1<=r2);
    switch(degree)
    {
        case 0:
        {
            assert (a*pow(r2,2)+b+epsilon>0 && a*pow(r1,2)+b+epsilon>0);
            return (std::sqrt(a*pow(r2,2)+b+epsilon) - std::sqrt(a*pow(r1,2)+b+epsilon))/a;
        }

        case 1:
        {
            assert(a*r1*r1+b+epsilon>0 && a*r2*r2+b+epsilon>0 && a>0);
            double temp1= std::sqrt(a)*std::sqrt(a*r1*r1 + b + epsilon);
            double temp2= std::sqrt(a)*std::sqrt(a*r2*r2 + b + epsilon);

            return ((r2*temp2-b*log(temp2+a*r2))-
                       (r1*temp1-b*log(temp1+a*r1)))/(2*pow(a,1.5));
        }
        default:
            MY_ERROR("Attempt to integrate polynomial of degree not equal to 0 or 1.");
    }

}

double MethodSphere::operator()(const Vector3d& vec) const
{
    double r= vec.norm();

    auto iter = std::find_if(piecewisePolynomial.cbegin(), piecewisePolynomial.cend(),
                          [=](const std::pair< std::pair<double,double>, Polynomial>& polynomial)
                          {
                             return r>=polynomial.first.first &&  r<polynomial.first.second;
                          });

    if (iter == piecewisePolynomial.end()) MY_ERROR("Argument out of range for the piecewise-defined weight function");
    return (iter->second)(r);
}

double MethodSphere::bondFunction(const Vector3d& vec1, const Vector3d& vec2) const
{
    double r1= vec1.norm();
    double r2= vec2.norm();

    double a= 4*(vec1-vec2).squaredNorm();
    double b= 4*pow(vec2.dot(vec1)-vec1.dot(vec1),2)-a*r1*r1;

    double sPerp= (vec1.dot(vec1)-vec2.dot(vec1))/(vec1-vec2).squaredNorm();

    Vector3d vecPerp;
    vecPerp= (1-sPerp)*vec1+sPerp*vec2;
    double rPerp= vecPerp.norm();
    assert(rPerp<std::min(r1,r2)+epsilon);

    double averagingDomainSize= getAveragingDomainSize();
    if (rPerp>=averagingDomainSize) return 0;

    r1= std::min(r1,averagingDomainSize);
    r2= std::min(r2,averagingDomainSize);

    double rmin;
    double rmax;
    double result= 0;
    if (sPerp<0 || sPerp>1)
    {
        rmin= std::min(r1,r2);
        rmax= std::max(r1,r2);

        if (abs(rmax-rmin)>epsilon) return integrate(a,b,rmin,rmax);
        else return 0;
    }
    else
    {
        rmin= rPerp;
        if (abs(r1-rmin)>epsilon) result= integrate(a,b,rmin,r1);
        if (abs(r2-rmin)>epsilon) result= result+integrate(a,b,rmin,r2);

        return result;
    }
    assert(0);
}

double MethodSphere::integrate(const double& a,
                        const double& b,
                        const double& rmin,
                        const double& rmax) const
{
    double averagingDomainSize= getAveragingDomainSize();
    assert(rmin<=rmax && rmax<=averagingDomainSize);
    double result= 0;
    auto iterMin = std::find_if(piecewisePolynomial.cbegin(), piecewisePolynomial.cend(),
                          [=](const std::pair< std::pair<double,double>, Polynomial>& polynomial)
                          {
                             return rmin>=polynomial.first.first &&  rmin<polynomial.first.second;
                          });
    if (iterMin == piecewisePolynomial.cend()) MY_ERROR("Lower integral limit out of range for the piecewise-defined weight function");
    auto iterMax = std::find_if(iterMin, piecewisePolynomial.cend(),
                          [=](const std::pair< std::pair<double,double>, Polynomial>& polynomial)
                          {
                             return rmax>=polynomial.first.first &&  rmax<polynomial.first.second;
                          });

    for(auto it=iterMin; it!=piecewisePolynomial.cend(); it++)
    {
        double lb,ub;
        if (it == iterMin) lb= rmin;
        else lb= it->first.first;
        if (it == iterMax) ub= rmax;
        else ub= it->first.second;

        int degree= 0;
        for(const auto& coefficient : it->second.coefficients)
        {
            result= result + 2*coefficient*integratePolynomial(degree,a,b,lb,ub);
            degree++;
        }

        if (it == iterMax) break;
    }
    return result;
}