F(t) - p = 0. We solve for t using newton's method.R/wei_series.R
qwei_series.RdQuantile function (inverse of the cdf).
By definition, the quantile p * 100% for a strictly monotonically increasing
cdf F is the value t that satisfies F(t) - p = 0.
We solve for t using newton's method.
qwei_series(p, shapes, scales, tol = 1e-05, t0 = 1)