code: def identity_matrix():
      """Return 4x4 identity/unit matrix.
  
      >>> I = identity_matrix()
      >>> numpy.allclose(I, numpy.dot(I, I))
      True
      >>> numpy.sum(I), numpy.trace(I)
      (4.0, 4.0)
      >>> numpy.allclose(I, numpy.identity(4))
      True
  
      """
      return numpy.identity(4)
  
imports: import math
  import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: identity_matrix() and returns: numpy