def compute_distances(self, model, alpha=None, ncat=4, tolerance=1e-6):
        """
        Compute pairwise distances between all sequences according to
        a given substitution model, `model`, of type phylo_utils.models.Model
        (e.g. phylo_utils.models.WAG(freqs), phylo_utils.models.GTR(rates, freqs))
        The number of gamma categories is controlled by `ncat`. Setting ncat=1
        disable gamma rate variation. The gamma alpha parameter must be supplied
        to enable gamma rate variation.
        """
        return pairdists(self, model, alpha, ncat, tolerance)