Moments 1..m-1 vanish, pushing the bias to O(h^m). A
non-negative function cannot have a vanishing second moment, so
orders above 2 necessarily take NEGATIVE values – the density can
go negative and the distribution non-monotone. Acceptable for
quantiles, where the estimand is a location; not for a density to
be plotted.
Examples
morie_fauzi_order_m_kernel(c(0, 1, 2), m = 4)$K
#> [1] 0.59841342 0.24197072 -0.02699548
