docs: def _jit_pairwise_distances(pos1, pos2):
          """Optimized function for calculating the distance between each pair
          of points in positions1 and positions2.
  
          Does use python mode as fallback, if a scalar and not an array is
          given.
          """
          n1 = pos1.shape[0]
          n2 = pos2.shape[0]
          D = np.empty((n1, n2))
  
          for i in range(n1):
              for j in range(n2):
                  D[i, j] = np.sqrt(((pos1[i] - pos2[j])**2).sum())
          return D