code: def der(self, x):
      dfdx = 2.0 * 3.0 * pi * cos(3.0 * pi * x[0]) * sin(
          3.0 * pi * x[0]
      ) + 2.0 * (x[0] - 1.0) * (1.0 + sin(3 * pi * x[1]) ** 2)
  
      dfdy = (
          (x[0] - 1.0) ** 2
          * 2.0
          * 3.0
          * pi
          * cos(3.0 * pi * x[1])
          * sin(3.0 * pi * x[1])
          + 2.0 * (x[1] - 1.0) * (1.0 + sin(2 * pi * x[1]) ** 2)
          + (x[1] - 1.0) ** 2
          * 2.0
          * 2.0
          * pi
          * cos(2.0 * pi * x[1])
          * sin(2.0 * pi * x[1])
      )
  
      return np.array([dfdx, dfdy])
  
imports: import time
  import numpy
  from numpy import sin, cos, pi, exp, sqrt, abs
  from scipy.optimize import rosen
label_desc: Use image node_id 2 for calling the Levi obj's underlying member method code with example usage: obj.der(x) and returns: np