code: def F3(x):
      A = np.array([[-2, 1, 0.0], [1, -2, 1], [0, 1, -2]])
      b = np.array([1, 2, 3.0])
      return A @ x - b
  
imports: from numpy.testing import assert_
  import pytest
  from scipy.optimize import nonlin, root
  from numpy import diag, dot
  from numpy.linalg import inv
  import numpy
  from .test_minpack import pressure_network
label_desc: Use image node_id 4 for calling a global function with example usage: F3(x) and returns: unknown