message: Switched to references in the index loops.
diff: @@ -79,14 +79,14 @@ vector<vector<float> > ACSF::create(vector<vector<float> > &positions, vector<in
  // Compute pairwise terms only for neighbors within cutoff
  vector<int> i_neighbours = neighbours[i];
  - for (int j : i_neighbours) {
  + for (int &j : i_neighbours) {
  if (i == j) {
  continue;
  }
  computeBond(output[index], atomicNumbers, distances, i, j);
  // Compute angle terms only when both neighbors are within cutoff
  - for (int k : i_neighbours) {
  + for (int &k : i_neighbours) {
  if (k == i || k >= j) {
  continue;
  }
  