ModularLambda gives the modular lambda elliptic function .
Mathematical function (see Section A.3.10).
ModularLambda is defined only in the upper half of the complex plane. It is not defined for real .
The argument is the ratio of Weierstrass half-periods .
ModularLambda gives the parameter for elliptic functions in terms of according to .
ModularLambda is related to EllipticTheta by where the nome is given by .
is invariant under any combination of the modular transformations and .
See Section 3.2.11 for a discussion of argument conventions for elliptic functions.
See The Mathematica Book: Section 3.2.11.
See also: DedekindEta, KleinInvariantJ, WeierstrassHalfPeriods.