compute_gravity.cc
70978a3ba845w12ex2_FR

compute_gravity.cc
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			#include "compute_gravity.hh"
			#include <cmath>
			/* -------------------------------------------------------------------------- */
			void ComputeGravity::compute(System &system) {

			UInt size = system.getNbParticles();
			// first of all reset forces to zero
			for (auto &particle : system)
			particle.getForce() = 0;

			// the force vector
			Vector force;
			// the distance vector
			Vector v_r;
			// the normalized vector
			Vector v_nr;
			// the square of the distance
			Real r2 = 0.;
			// the distance
			Real r = 0.;

			for (UInt p1 = 0; p1 < size; ++p1) {
			Particle &par1 = system.getParticle(p1);
			for (UInt p2 = p1 + 1; p2 < size; ++p2) {
			Particle &par2 = system.getParticle(p2);

			// compute the distance vector and the square of distance

			v_r = par2.getPosition() - par1.getPosition();
			r2 = v_r.squaredNorm();

			if (r2 == 0.)
			continue;
			// compute the distance
			r = sqrt(r2);
			v_nr = v_r / r;

			// compute the pair force
			force = par1.getMass() * par2.getMass() * G / r2 * v_nr;

			// add up the force for both concerned particles
			par2.getForce() -= force;
			par1.getForce() += force;
			}
			}
			}
			/* -------------------------------------------------------------------------- */
			void ComputeGravity::setG(Real G) { this->G = G; }