Fit a VAR model to the source activations.

        Returns
        -------
        self : Workspace
            The Workspace object.

        Raises
        ------
        RuntimeError
            If the :class:`Workspace` instance does not contain source activations.

def fit_var(self):
        """ Fit a VAR model to the source activations.

        Returns
        -------
        self : Workspace
            The Workspace object.

        Raises
        ------
        RuntimeError
            If the :class:`Workspace` instance does not contain source activations.
        """
        if self.activations_ is None:
            raise RuntimeError("VAR fitting requires source activations (run do_mvarica first)")
        self.var_.fit(data=self.activations_[self.trial_mask_, :, :])
        self.connectivity_ = Connectivity(self.var_.coef, self.var_.rescov, self.nfft_)
        return self