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lammps/lib/atc/Quadrature.cpp
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Quadrature.cpp
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#include "Quadrature.h"
#include <cmath>
#include "ATC_Error.h"
using namespace std;
namespace ATC {
Quadrature * Quadrature::myInstance_ = NULL;
// -----------------------------------------------------------------
// instance()
// -----------------------------------------------------------------
Quadrature * Quadrature::instance()
{
if (myInstance_ == NULL) {
myInstance_ = new Quadrature();
}
return myInstance_;
}
// -----------------------------------------------------------------
// Destroy()
// -----------------------------------------------------------------
void Quadrature::Destroy()
{
if (myInstance_) delete myInstance_;
myInstance_ = NULL;
}
// -----------------------------------------------------------------
// constructor
// -----------------------------------------------------------------
Quadrature::Quadrature()
{
}
// -----------------------------------------------------------------
// line quadrature: positions & weights
// -----------------------------------------------------------------
/** domain of integration is -1 to 1 */
void Quadrature::set_line_quadrature(const int ng, double* xg, double* wg)
{
/** integration schemes : 3, 4, 5, 10 point Gauss */
if (ng == 3) {
xg[0] = 0.0; wg[0] = 8.0/9.0;
xg[1] = -sqrt(3.0/5.0); wg[1] = 5.0/9.0;
xg[2] = sqrt(3.0/5.0); wg[2] = 5.0/9.0;
}
else if (ng == 4) {
xg[0] = -sqrt((3.0/7.0)-(sqrt(120.0)/35.0)); wg[0] = (1.0/2.0)+(5.0/(3.0*sqrt(120.0)));
xg[1] = sqrt((3.0/7.0)-(sqrt(120.0)/35.0)); wg[1] = (1.0/2.0)+(5.0/(3.0*sqrt(120.0)));
xg[2] = -sqrt((3.0/7.0)+(sqrt(120.0)/35.0)); wg[2] = (1.0/2.0)-(5.0/(3.0*sqrt(120.0)));
xg[3] = sqrt((3.0/7.0)+(sqrt(120.0)/35.0)); wg[3] = (1.0/2.0)-(5.0/(3.0*sqrt(120.0)));
}
else if (ng == 5) {
xg[0] = 0.0; wg[0] = 0.5688888888888889;
xg[1] = -sqrt((35.0-sqrt(280.0))/63.0); wg[1] = 0.4786286704993658;
xg[2] = sqrt((35.0-sqrt(280.0))/63.0); wg[2] = 0.4786286704993658;
xg[3] = -sqrt((35.0+sqrt(280.0))/63.0); wg[3] = 0.2369268850561891;
xg[4] = sqrt((35.0+sqrt(280.0))/63.0); wg[4] = 0.2369268850561891;
}
else if (ng == 10) {
xg[0] = -0.14887434; wg[0] = 0.29552422;
xg[1] = 0.14887434; wg[1] = 0.29552422;
xg[2] = -0.43339539; wg[2] = 0.26926672;
xg[3] = 0.43339539; wg[3] = 0.26926672;
xg[4] = -0.67940957; wg[4] = 0.21908636;
xg[5] = 0.67940957; wg[5] = 0.21908636;
xg[6] = -0.86506337; wg[6] = 0.14945135;
xg[7] = 0.86506337; wg[7] = 0.14945135;
xg[8] = -0.97390653; wg[8] = 0.06667134;
xg[9] = 0.97390653; wg[9] = 0.06667134;
}
else {
throw ATC_Error("Invalid choice of number of quadrature points");
}
}
} // end namespace
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