These functions provide information about the two-sided power distribution
with location parameter equal to m and shape equal to
s: density, cumulative distribution, quantiles, and
random generation.
The two-sided power distribution has density
$$
f(y) = s(\frac{y}{m})^{s-1}, y<=m$$
$$
f(y) =s(\frac{1-y}{1-m})^{s-1}, y>=m$$
where \(\mu\) is the location parameter of the distribution and
\(\sigma\) is the shape, and \(0<y<1\).
For \(\sigma=1\), this is the uniform distribution and for
\(\sigma=2\), it is the triangular distribution.