code: def create_normal_matrix(self, modelview):
          
          normal_m = Matrix33.from_matrix44(modelview)
          normal_m = normal_m.inverse
          normal_m = normal_m.transpose()
          return normal_m
docs: Creates a normal matrix from modelview matrix
  
          Args:
              modelview: The modelview matrix
  
          Returns:
              A 3x3 Normal matrix as a :py:class:`numpy.array`