'returns interpolated quantiles, similar to ppf or isf
uses Rbf to interpolate critical values as function of `prob` and `n`
Parameters
prob : array_like
probabilities corresponding to the definition of table columns
n : int or float
sample size, second parameter of the table
Returns
ppf : array_like
critical values with same shape as prob, returns nan for arguments
that are outside of the table bounds'

def crit3(self, prob, n):

    prob = np.asarray(prob)
    alpha = self.alpha
    cond_ilow = (prob > alpha[0])
    cond_ihigh = (prob < alpha[(-1)])
    cond_interior = np.logical_or(cond_ilow, cond_ihigh)
    if (prob.size == 1):
        if cond_interior:
            return self.polyrbf(n, prob)
        else:
            return np.nan
    quantile = (np.nan * np.ones(prob.shape))
    quantile[cond_interior] = self.polyrbf(n, prob[cond_interior])
    return quantile
