compute_gravity.cc
e16a226e15f1w12ex2_FR

compute_gravity.cc
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			#include "compute_gravity.hh"
			#include <cmath>
			/* -------------------------------------------------------------------------- */
			void ComputeGravity::compute(System& system) {
			// define a lambda function for newtonian gravity
			auto newton_gravity = [this](Particle& par1, Particle& par2) {
			// compute the distance vector and the square of distance
			auto v_r = par2.getPosition() - par1.getPosition();
			auto r2 = v_r.squaredNorm();

			if (r2 == 0.)
			return;

			// compute the distance
			auto r = sqrt(r2);
			v_r *= 1 / r;

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

			// add up the force for both concerned particles
			par2.getForce() -= force;
			par1.getForce() += force;
			};

			// apply newtonian gravity on all pairs of particles
			applyOnPairs(newton_gravity, system);
			}

			/* -------------------------------------------------------------------------- */
			void ComputeGravity::setG(Real G) { this->G = G; }