Deterministic evaluation and holonomic structure for moderate sample sizes
Determine, for each fixed sample size n, the order of a linear differential equation with polynomial coefficients satisfied by the Jarque–Bera density f_{JB_n}(x), and determine whether this equation is ever of hypergeometric (first-order recurrence) type, thereby enabling deterministic evaluation of the distribution function by the holonomic gradient method.
References
Determine the order of the equation as a function of $n$ and whether it is ever of hypergeometric (first-order recurrence) type.
For $n\ge6$ the minimum set ${S_n=0,K_n=3}$ has positive dimension, so the stationary points are no longer isolated, and the remaining stationary points have not been classified. For the joint density the classification is open beyond the cases treated here: for $n=4$ the singularities are inverse-square-root at the edges of the support, and for $n=5$ the density jumps at the boundary and is logarithmic along interior curves (Section~\ref{sec:n5}).