code: def evaluate(x, y, constant, amplitude, x_mean, y_mean, x_stddev,
                   y_stddev, theta):
          
  
          model = Const2D(constant)(x, y) + Gaussian2D(amplitude, x_mean,
                                                       y_mean, x_stddev,
                                                       y_stddev, theta)(x, y)
          return model
docs: Two dimensional Gaussian plus constant function.