This function returns a random variate from the Weibull distribution. The distribution function is,
for \(x \geq 0\).
This function computes the probability density \(p(x)\) at \(x\) for a Weibull distribution with scale a and exponent b, using the formula given above.
These functions compute the cumulative distribution functions \(P(x), Q(x)\) and their inverses for the Weibull distribution with scale a and exponent b.