…
►where
is a simple closed contour described in the positive rotational sense such that
and its interior lie in the domain of analyticity of
, and
is interior
to
.
Taking
to be a circle of radius
centered at
, we obtain
…
►
First-Order
…
►
Second-Order
…
►
Fourth-Order
…
…
►for all
sufficiently large, where
and
are independent of
, then the sequence is said
to have
convergence of the
th
order.
…
…
►This is useful when
satisfies a second-
order linear differential equation because of the ease of computing
.
…
►Consider
and
.
We have
and
.
…
…
►Having now directly connected computation of the quadrature abscissas and weights
to the moments, what follows uses these for a Stieltjes–Perron
inversion to regain
.
…
►The question is then: how is this possible given only
, rather than
itself?
often converges
to smooth results for
off the real axis for
at a distance greater than the pole spacing of the
, this may then be followed by
approximate numerical analytic continuation via fitting
to lower
order continued fractions (either Padé, see §
3.11(iv), or pointwise continued fraction approximants, see
Schlessinger (1968, Appendix)),
to
and evaluating these on the real axis in regions of higher pole density that those of the approximating function.
Results of low (
to
decimal digits) precision for
are easily obtained for
to
.
…
►Interpolation of the midpoints of the jumps followed by differentiation with
respect to
yields a Stieltjes–Perron inversion
to obtain
to a precision of
decimal digits for
.
…
►Further,
exponential convergence in
, via the Derivative Rule, rather than the power-law convergence of the histogram methods, is found for the inversion of Gegenbauer, Attractive, as well as Repulsive, Coulomb–Pollaczek, and Hermite weights and zeros
to approximate
for these OP systems on
and
respectively,
Reinhardt (2018), and
Reinhardt (2021b),
Reinhardt (2021a).
…
…
►When
,
has a string of complex zeros that approaches the ray
as
, and a conjugate string.
…
►Numerical calculations in this case show that
corresponds
to the
th zero on the string; compare §
7.13(ii).
…
►For example, let the
th real zeros of
and
, counted in descending
order away from the point
, be denoted by
and
,
respectively.
…as
(
)
,
fixed.
…where
is the function inverse
to
, defined by (
12.10.39) (see also (
12.10.41)), and
…