Is the code in gravity_calculate_acceleration correct? I think 'j' will always be 0 in the inner-loop, which seems to defeat the purpose of having a j variable.

Is the code in gravity_calculate_acceleration correct? I think 'j' will always be 0 in the inner-loop, which seems to defeat the purpose of having a j variable. void gravity_calculate_acceleration(int n_particles, double m[], double x[][3], double a[][3]) { double G = 6.6742367e-11; // m^3.kg^-1.s^-2 for (int i=0; i<n_particles; i++){ a[i][0] = 0; a[i][1] = 0; a[i][2] = 0; for (int j=0; i<n_particles; i++){ if (j == i) { continue; } double dx = x[i][0] - x[j][0]; double dy = x[i][0] - x[j][0]; double dz = x[i][0] - x[j][0]; double r = sqrt(dx*dx + dy*dy + dz*dz); double prefact = -G/(r*r*r) * m[j]; a[i][0] += prefact * dx; a[i][1] += prefact * dy; a[i][2] += prefact * dz; } } }