def save_sparse_data(self, fname):
        """Saves the tuple (raw_data,all_cell_names,all_gene_names) in a
        Pickle file.

        Parameters
        ----------
        fname - string
            The filename of the output file.

        """
        data = self.adata_raw.X.T
        if data.getformat()=='csr':
            data=data.tocsc()

        cell_names = np.array(list(self.adata_raw.obs_names))
        gene_names = np.array(list(self.adata_raw.var_names))
        
        pickle.dump((data, cell_names, gene_names), open(fname, 'wb'))
Saves the tuple (raw_data,all_cell_names,all_gene_names) in a
        Pickle file.

        Parameters
        ----------
        fname - string
            The filename of the output file.