Returns a structured description of the model, including (where relevant)
        the schema of the training data, description of the training data,
        training statistics, and model hyperparameters.

        Returns
        -------
        sections : list (of list of tuples)
            A list of summary sections.
              Each section is a list.
                Each item in a section list is a tuple of the form:
                  ('<label>','<field>')
        section_titles: list
            A list of section titles.
              The order matches that of the 'sections' object.

def _get_summary_struct(self):
        """
        Returns a structured description of the model, including (where relevant)
        the schema of the training data, description of the training data,
        training statistics, and model hyperparameters.

        Returns
        -------
        sections : list (of list of tuples)
            A list of summary sections.
              Each section is a list.
                Each item in a section list is a tuple of the form:
                  ('<label>','<field>')
        section_titles: list
            A list of section titles.
              The order matches that of the 'sections' object.
        """
        section_titles=['Schema','Settings']

        vocab_length = len(self.vocabulary)
        verbose = self.verbose == 1

        sections=[
                    [
                        ('Vocabulary Size',_precomputed_field(vocab_length))
                    ],
                    [
                        ('Number of Topics', 'num_topics'),
                        ('alpha','alpha'),
                        ('beta','beta'),
                        ('Iterations', 'num_iterations'),
                        ('Training time', 'training_time'),
                        ('Verbose', _precomputed_field(verbose))
                    ]
                ]
        return (sections, section_titles)