code: def F2(x):
      return x
  
imports: from numpy.testing import assert_
  import pytest
  from scipy.optimize import _nonlin, root
  from scipy.sparse import csr_array
  from numpy import diag, dot
  from numpy.linalg import inv
  import numpy
  from .test_minpack import pressure_network
label_desc: Use image node_id 2 for calling a global function with example usage: F2(x) and returns: x