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