…
►Suppose that the invariants
,
, are given, for example in the differential equation (
23.3.10) or via coefficients of an elliptic curve (§
23.20(ii)).
…
►
(a)
In the general case, given by , we compute the roots ,
, , say, of the cubic equation ; see
§1.11(iii). These roots are necessarily distinct and represent ,
, in some order.
If and are real, and the discriminant is positive, that is ,
then , , can be identified via
(23.5.1), and , obtained from (23.6.16).
If , or and are not both real, then we label , , so
that the triangle with vertices , , is positively
oriented and is its longest side (chosen arbitrarily if
there is more than one). In particular, if , , are
collinear, then we label them so that is on the line segment
. In consequence, ,
satisfy
(with strict inequality unless
, , are collinear); also , .
Finally, on taking the principal square roots of and we obtain
values for and that lie in the 1st and 4th quadrants, respectively,
and , are given by
23.22.1
where denotes the arithmetic-geometric mean (see §§19.8(i) and
22.20(ii)). This process yields 2 possible pairs
(, ), corresponding to the 2 possible choices of the
square root.
►
(b)
If , then
23.22.2
There are 4 possible pairs (, ), corresponding to the
4 rotations of a square lattice. The lemniscatic case occurs when and
.
►
(c)
If , then
23.22.3
There are 6 possible pairs (, ), corresponding to the
6 rotations of a lattice of equilateral triangles. The equianharmonic case
occurs when and .
…
►Assume
and
.
…
…
►be a nonlinear second-order differential equation in which
is a rational function of
and
, and is
locally analytic in
, that is, analytic except for isolated singularities in
.
…
►in which
,
,
,
, and
are locally analytic functions.
…
►where
,
,
are constants,
,
,
are functions of
, with
…
►where
,
,
,
are constants,
,
,
,
are functions of
, with
…
►then as
,
satisfies
with
,
,
,
,
.
…
…
►
9.12.21
►If
or
, and
is the modified Bessel function (§
10.25(ii)), then
►
9.12.22
,
…
►
9.12.24
►where the integration contour separates the poles of
from those of
.
…
…
►If
and
are nonzero real or complex numbers such that
, then the set of points
, with
, constitutes a
lattice
with
and
lattice generators.
…
►then
,
are generators, as are
,
.
…where
are integers, then
,
are generators of
iff
…
►For
, the function
satisfies
…More generally, if
,
,
, and
, then
…
…
►
denotes the number of partitions of
into parts with difference at least
3, except that multiples of
3 must differ by at least 6.
…The set
is denoted by
.
…
►where the sum is over nonnegative integer values of
for which
.
…
►Note that
, with strict inequality for
.
It is known that for
,
, with strict inequality for
sufficiently large, provided that
, or
; see
Yee (2004).
…
…
►In the following formulas for the coefficients
,
,
, and
,
,
are the constants defined in §
9.7(i), and
,
are the polynomials in
of degree
defined in §
10.41(ii).
…
►In formulas (
10.20.10)–(
10.20.13) replace
,
,
, and
by
,
,
, and
, respectively.
►Note: Another way of arranging the above formulas for the coefficients
, and
would be by analogy with (
12.10.42) and (
12.10.46).
…
►Each of the coefficients
,
,
, and
,
, is real and infinitely differentiable on the interval
.
…
►The equations of the curved boundaries
and
in the
-plane are given parametrically by
…
…
►is
in cycle notation.
…In consequence, (
26.13.2) can also be written as
.
…
►The
derangement number,
, is the number of elements of
with no fixed points:
…
►For the example (
26.13.2), this decomposition is given by
…
►Again, for the example (
26.13.2) a minimal decomposition into adjacent transpositions is given by
:
.
…
►
9.2.3
►
9.2.4
►
9.2.5
►
9.2.6
…
►
, where
is any nontrivial solution of (
9.2.1).
…