This function returns a random variate from the Laplace distribution with width a. The distribution is,
for \(-\infty < x < \infty\).
This function computes the probability density \(p(x)\) at \(x\) for a Laplace distribution with width a, using the formula given above.
These functions compute the cumulative distribution functions \(P(x), Q(x)\) and their inverses for the Laplace distribution with width a.