void InitializeSystem(vector<Particle>& p, double box, int nSideX, int nSideY) { int N=nSideX*nSideY; p.resize(N); RNG rng; const Vector2D centerer = Vector2D(-0.5,-0.5)*box; const double stepX = box/nSideX; const double stepY = box/nSideY; int idx = 0; for (int i=0; i<nSideX; i++) { for (int j=0; j<nSideY; j++) { p[idx].r = Vector2D(i*stepX,j*stepY) + centerer; p[idx].v = Vector2D(rng.UniCentered(), rng.UniCentered()); idx++; } } }