# n-body problem parallel code in c++ example 1

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``````#include <cmath>
#include <iostream>
#include <vector>
#include <omp.h>

const double G = 6.674e-11;  // gravitational constant

struct Body {
double x, y, z;  // position
double vx, vy, vz;  // velocity
double mass;  // mass
};

// Calculate the gravitational force between two bodies.
void gravitationalForce(Body &body1, Body &body2, double &fx, double &fy, double &fz) {
double dx = body2.x - body1.x;
double dy = body2.y - body1.y;
double dz = body2.z - body1.z;
double distSqr = dx * dx + dy * dy + dz * dz;
double f = G * body1.mass * body2.mass / distSqr;
double fx = f * dx / distSqr;
double fy = f * dy / distSqr;
double fz = f * dz / distSqr;
}

int main() {
std::vector<Body> bodies;
// Initialize the array of bodies with their positions, velocities, and masses.

double dt = 0.01;  // time step
for (int t = 0; t < 100; ++t) {  // simulate for 100 time steps
// Use OpenMP to parallelize the loop over all pairs of bodies.
#pragma omp parallel for
for (int i = 0; i < bodies.size(); ++i) {
for (int j = i + 1; j < bodies.size(); ++j) {
Body &body1 = bodies[i];
Body &body2 = bodies[j];
double fx, fy, fz;
gravitationalForce(body1, body2, fx, fy, fz);
body1.vx += dt * fx / body1.mass;
body1.vy += dt * fy / body1.mass;
body1.vz += dt * fz / body1.mass;
body2.vx -= dt * fx / body2.mass;
body2.vy -= dt * fy / body2.mass;
body2.vz -= dt * fz / body2.mass;
}
}

// Update the position of each body according to its velocity.
for (Body &body : bodies) {
body.x += dt * body.vx;
body.y += dt * body.vy;
body.z += dt * body.vz;
}
}

return 0;
}``````  • Rulesets
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