Random: double gsl_ran_exppow(const gsl_rng * r, double a, double b)
This function returns a random variate from the exponential power distribution
with scale parameter a and exponent b. The distribution is,
for @c{$x \ge 0$}
@math{x >= 0}. For @math{b = 1} this reduces to the Laplace
distribution. For @math{b = 2} it has the same form as a gaussian
distribution, but with @c{$a = \sqrt{2} \sigma$}
@math{a = \sqrt{2} \sigma}.
Function: double gsl_ran_exppow_pdf(double x, double a, double b)
This function computes the probability density @math{p(x)} at x
for an exponential power distribution with scale parameter a
and exponent b, using the formula given above.