def METHOD_NAME(self):
    """
    Create a tau model from a velocity model.
    Called by :func:`build_taup_model` after :meth:`load_velocity_model`;
    calls :meth:`create_tau_model` and writes the result to a ``.npy``
    file.
    """
    try:
        self.tau_model = self.create_tau_model(self.v_mod)
        # this reassigns model! Used to be TauModel() class,
        # now it's an instance of it.
        if self.debug:
            print("Done calculating Tau branches.")
        dirname = os.path.dirname(self.output_filename)
        if dirname and not os.path.exists(dirname):
            os.makedirs(dirname)
        self.tau_model.serialize(self.output_filename)
        if self.debug:
            print("Done Saving " + str(self.output_filename))
    except IOError as e:
        print("Tried to write!\n Caught IOError. Do you have write "
              "permission in this directory?", e)
    except KeyError as e:
        print('file not found or wrong key?', e)
    finally:
        if self.debug:
            print("Method run is done, but not necessarily successful.")