KleinInvariantJ
✖
KleinInvariantJ
Details

- Mathematical function, suitable for both symbolic and numerical manipulation.
- The argument
is the ratio of Weierstrass half‐periods
.
- KleinInvariantJ is given in terms of Weierstrass invariants by
.
is invariant under any combination of the modular transformations
and
.
- For certain special arguments, KleinInvariantJ automatically evaluates to exact values.
- KleinInvariantJ can be evaluated to arbitrary numerical precision.
- KleinInvariantJ can be used with CenteredInterval objects. »
- KleinInvariantJ automatically threads over lists.
Examples
open allclose allBasic Examples (4)Summary of the most common use cases

https://wolfram.com/xid/0k8a40838oxfl-ckejc9

Plot over a subset of the reals:

https://wolfram.com/xid/0k8a40838oxfl-no8at3

Plot over a subset of the complexes:

https://wolfram.com/xid/0k8a40838oxfl-dz7y0w

Series expansion at the origin:

https://wolfram.com/xid/0k8a40838oxfl-f65ufv

Scope (23)Survey of the scope of standard use cases
Numerical Evaluation (5)

https://wolfram.com/xid/0k8a40838oxfl-l274ju


https://wolfram.com/xid/0k8a40838oxfl-cksbl4


https://wolfram.com/xid/0k8a40838oxfl-b0wt9

The precision of the output tracks the precision of the input:

https://wolfram.com/xid/0k8a40838oxfl-y7k4a

Evaluate efficiently at high precision:

https://wolfram.com/xid/0k8a40838oxfl-di5gcr


https://wolfram.com/xid/0k8a40838oxfl-bq2c6r

KleinInvariantJ can be used with CenteredInterval objects:

https://wolfram.com/xid/0k8a40838oxfl-cmdnbi

Compute average-case statistical intervals using Around:

https://wolfram.com/xid/0k8a40838oxfl-cw18bq

Specific Values (2)

https://wolfram.com/xid/0k8a40838oxfl-cgkwdk


https://wolfram.com/xid/0k8a40838oxfl-g3uy25

Find the first positive maximum of the real part of KleinInvariantJ:

https://wolfram.com/xid/0k8a40838oxfl-f2hrld


https://wolfram.com/xid/0k8a40838oxfl-kjeo7

Visualization (2)
Plot the real part of KleinInvariantJ:

https://wolfram.com/xid/0k8a40838oxfl-b1j98m

Plot the real part of J(τ) function:

https://wolfram.com/xid/0k8a40838oxfl-kgd8nu

Plot the imaginary part of J(τ) function:

https://wolfram.com/xid/0k8a40838oxfl-dn1q3j

Function Properties (10)
Complex domain of KleinInvariantJ:

https://wolfram.com/xid/0k8a40838oxfl-cl7ele

KleinInvariantJ is a periodic function:

https://wolfram.com/xid/0k8a40838oxfl-rs6ggw

KleinInvariantJ threads elementwise over lists:

https://wolfram.com/xid/0k8a40838oxfl-l3y8sq

KleinInvariantJ is an analytic function on its domain of definition:

https://wolfram.com/xid/0k8a40838oxfl-tcco7w

It has no singularities or discontinuities there:

https://wolfram.com/xid/0k8a40838oxfl-mdtl3h


https://wolfram.com/xid/0k8a40838oxfl-zm16u

is neither nondecreasing nor nonincreasing:

https://wolfram.com/xid/0k8a40838oxfl-nlz7s

KleinInvariantJ is not injective over the complexes:

https://wolfram.com/xid/0k8a40838oxfl-l8bif1


https://wolfram.com/xid/0k8a40838oxfl-cxk3a6


https://wolfram.com/xid/0k8a40838oxfl-frlnsr

is neither non-negative nor non-positive:

https://wolfram.com/xid/0k8a40838oxfl-84dui

is neither convex nor concave:

https://wolfram.com/xid/0k8a40838oxfl-8kku21

TraditionalForm formatting:

https://wolfram.com/xid/0k8a40838oxfl-pempl

Differentiation (2)
First derivative with respect to τ:

https://wolfram.com/xid/0k8a40838oxfl-krpoah

The first and second derivatives with respect to τ:

https://wolfram.com/xid/0k8a40838oxfl-z33jv

Plot the first and second derivatives with respect to τ:

https://wolfram.com/xid/0k8a40838oxfl-fxwmfc

Series Expansions (2)
Find the Taylor expansion using Series:

https://wolfram.com/xid/0k8a40838oxfl-ewr1h8

Plots of the first three approximations around :

https://wolfram.com/xid/0k8a40838oxfl-binhar

Taylor expansion at a generic point:

https://wolfram.com/xid/0k8a40838oxfl-jwxla7

Applications (7)Sample problems that can be solved with this function
Some modular properties of KleinInvariantJ are automatically applied:

https://wolfram.com/xid/0k8a40838oxfl-w4a81

Verify a more complicated identity numerically:

https://wolfram.com/xid/0k8a40838oxfl-cf3t3e

Find values at quadratic irrationals:

https://wolfram.com/xid/0k8a40838oxfl-d0k7yw


https://wolfram.com/xid/0k8a40838oxfl-gdgjqo

KleinInvariantJ is a modular function. Make an ansatz for a modular equation:

https://wolfram.com/xid/0k8a40838oxfl-eoyrpk

Form an overdetermined system of equations and solve it:

https://wolfram.com/xid/0k8a40838oxfl-cbq49u

https://wolfram.com/xid/0k8a40838oxfl-e4brb


This is the modular equation of order 2:

https://wolfram.com/xid/0k8a40838oxfl-b2rpai

Solution of the Chazy equation :

https://wolfram.com/xid/0k8a40838oxfl-dycq1m

https://wolfram.com/xid/0k8a40838oxfl-g872su

Plot the absolute value in the complex plane:

https://wolfram.com/xid/0k8a40838oxfl-fc47ot

Plot the imaginary part in the complex plane:

https://wolfram.com/xid/0k8a40838oxfl-jn2576

Define the discriminant of the Weierstrass elliptic curve:

https://wolfram.com/xid/0k8a40838oxfl-bxz1na

It can be computed as the ratio of a power of invariant and the discriminant:

https://wolfram.com/xid/0k8a40838oxfl-m7mjw

https://wolfram.com/xid/0k8a40838oxfl-mjpanl

Compare with the built‐in function value:

https://wolfram.com/xid/0k8a40838oxfl-cm8vjo

Properties & Relations (2)Properties of the function, and connections to other functions
Possible Issues (2)Common pitfalls and unexpected behavior
Machine-precision input may be insufficient to give the correct answer:

https://wolfram.com/xid/0k8a40838oxfl-d2vmya

With exact input, the answer is correct:

https://wolfram.com/xid/0k8a40838oxfl-ez22mu

KleinInvariantJ remains unevaluated outside of its domain of analyticity:

https://wolfram.com/xid/0k8a40838oxfl-ibrfdg


https://wolfram.com/xid/0k8a40838oxfl-eq2fvz

Wolfram Research (1996), KleinInvariantJ, Wolfram Language function, https://reference.wolfram.com/language/ref/KleinInvariantJ.html (updated 2021).
Text
Wolfram Research (1996), KleinInvariantJ, Wolfram Language function, https://reference.wolfram.com/language/ref/KleinInvariantJ.html (updated 2021).
Wolfram Research (1996), KleinInvariantJ, Wolfram Language function, https://reference.wolfram.com/language/ref/KleinInvariantJ.html (updated 2021).
CMS
Wolfram Language. 1996. "KleinInvariantJ." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2021. https://reference.wolfram.com/language/ref/KleinInvariantJ.html.
Wolfram Language. 1996. "KleinInvariantJ." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2021. https://reference.wolfram.com/language/ref/KleinInvariantJ.html.
APA
Wolfram Language. (1996). KleinInvariantJ. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/KleinInvariantJ.html
Wolfram Language. (1996). KleinInvariantJ. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/KleinInvariantJ.html
BibTeX
@misc{reference.wolfram_2025_kleininvariantj, author="Wolfram Research", title="{KleinInvariantJ}", year="2021", howpublished="\url{https://reference.wolfram.com/language/ref/KleinInvariantJ.html}", note=[Accessed: 08-June-2025
]}
BibLaTeX
@online{reference.wolfram_2025_kleininvariantj, organization={Wolfram Research}, title={KleinInvariantJ}, year={2021}, url={https://reference.wolfram.com/language/ref/KleinInvariantJ.html}, note=[Accessed: 08-June-2025
]}