code: def _dx_shapelets(self, shapelets, beta):
          
          num_n = len(shapelets)
          dx = np.zeros((num_n+1, num_n+1))
          for n1 in range(num_n):
              for n2 in range(num_n):
                  amp = shapelets[n1][n2]
                  dx[n1+1][n2] -= np.sqrt((n1+1)/2.) * amp
                  if n1 > 0:
                      dx[n1-1][n2] += np.sqrt(n1/2.) * amp
          return dx/beta
docs: computes the derivative d/dx of the shapelet coeffs
          :param shapelets:
          :param beta:
          :return: