GeneralizedInverseGaussianPDF

auto pdf = new GeneralizedInverseGaussianPDF!double(3, 2, 1);
auto x = pdf(0.1);
assert(x.isNormal);

import scid.calculus : integrate;
auto result = pdf.integrate(-double.infinity, double.infinity);
assert(fabs(result.value - 1) < result.error);