Number of registered stages for given matrix name.

        Parameters:
            matrix_name (str): name of the matrix

        Returns:
            int: number of reported stages for given matrix name.

def count_stages(self, matrix_name):
        """
        Number of registered stages for given matrix name.

        Parameters:
            matrix_name (str): name of the matrix

        Returns:
            int: number of reported stages for given matrix name.
        """
        return len(self.data[matrix_name]) if matrix_name in self.data else 0