def date_uncertainty_due_to_rate(self, node, interval=(<NUM_LIT>, <NUM_LIT>)):
if hasattr(node, "<STR_LIT>"):<EOL><INDENT>from scipy.special import erfinv<EOL>nsig = [np.sqrt(<NUM_LIT>)*erfinv(-<NUM_LIT:1.0> + <NUM_LIT>*x) if x*(<NUM_LIT:1.0>-x) else <NUM_LIT:0><EOL>for x in interval]<EOL>l,c,u = [x[<NUM_LIT:1>] for x in node.numdate_rate_variation]<EOL>return np.array([c + x*np.abs(y-c) for x,y in zip(nsig, (l,u))])<EOL><DEDENT>else:<EOL><INDENT>return None<EOL><DEDENT>
use previously calculated variation of the rate to estimate
        the uncertainty in a particular numdate due to rate variation.

        Parameters
        ----------
        node : PhyloTree.Clade
            node for which the confidence interval is to be calculated
        interval : tuple, optional
            Array of length two, or tuple, defining the bounds of the confidence interval