WOLFRAM

gives the Klein invariant modular elliptic function TemplateBox[{tau}, KleinInvariantJ].

Details

  • Mathematical function, suitable for both symbolic and numerical manipulation.
  • The argument is the ratio of Weierstrass halfperiods .
  • KleinInvariantJ is given in terms of Weierstrass invariants by .
  • TemplateBox[{tau}, KleinInvariantJ] 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

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Basic Examples  (4)Summary of the most common use cases

Evaluate numerically:

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Plot over a subset of the reals:

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Plot over a subset of the complexes:

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Series expansion at the origin:

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Scope  (23)Survey of the scope of standard use cases

Numerical Evaluation  (5)

Evaluate numerically:

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Evaluate to high precision:

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

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Evaluate efficiently at high precision:

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KleinInvariantJ can be used with CenteredInterval objects:

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Compute average-case statistical intervals using Around:

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Specific Values  (2)

Values at fixed points:

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

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Visualization  (2)

Plot the real part of KleinInvariantJ:

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Plot the real part of J(τ) function:

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Plot the imaginary part of J(τ) function:

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Function Properties  (10)

Complex domain of KleinInvariantJ:

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KleinInvariantJ is a periodic function:

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KleinInvariantJ threads elementwise over lists:

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KleinInvariantJ is an analytic function on its domain of definition:

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It has no singularities or discontinuities there:

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Re(TemplateBox[{{x, +, ⅈ}}, KleinInvariantJ]) is neither nondecreasing nor nonincreasing:

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KleinInvariantJ is not injective over the complexes:

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Re(TemplateBox[{{x, +, ⅈ}}, KleinInvariantJ]) is not surjective:

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Re(TemplateBox[{{x, +, ⅈ}}, KleinInvariantJ]) is neither non-negative nor non-positive:

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Re(TemplateBox[{{x, +, ⅈ}}, KleinInvariantJ]) is neither convex nor concave:

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TraditionalForm formatting:

Differentiation  (2)

First derivative with respect to τ:

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The first and second derivatives with respect to τ:

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Plot the first and second derivatives with respect to τ:

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Series Expansions  (2)

Find the Taylor expansion using Series:

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Plots of the first three approximations around :

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Taylor expansion at a generic point:

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Applications  (7)Sample problems that can be solved with this function

Some modular properties of KleinInvariantJ are automatically applied:

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Verify a more complicated identity numerically:

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Find values at quadratic irrationals:

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

Form an overdetermined system of equations and solve it:

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This is the modular equation of order 2:

Solution of the Chazy equation :

Plot the solution:

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Plot the absolute value in the complex plane:

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Plot the imaginary part in the complex plane:

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Define the discriminant of the Weierstrass elliptic curve:

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

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Compare with the builtin function value:

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Properties & Relations  (2)Properties of the function, and connections to other functions

Find derivatives:

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Find a numerical root:

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Possible Issues  (2)Common pitfalls and unexpected behavior

Machine-precision input may be insufficient to give the correct answer:

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With exact input, the answer is correct:

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KleinInvariantJ remains unevaluated outside of its domain of analyticity:

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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).

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 ]}

@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 ]}

@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 ]}