code: def get_duration(self, matrix_name):
          
          duration = 0.0
          if matrix_name in self.data:
              duration = sum([stage.duration() for stage in self.data[matrix_name]])
          return duration
docs: Get duration for a concrete matrix.
  
          Args:
              matrix_name (str): name of the Matrix.
  
          Returns:
              float: duration of concrete matrix in seconds.