What is the relationship between holomorphic maps and elliptic functions?

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Discussion Overview

The discussion revolves around the relationship between holomorphic maps and elliptic functions, specifically focusing on the properties of functions mapping from the complex plane modulo a lattice (C/(Z+iZ)) to itself. Participants explore the conditions under which these functions are doubly periodic and their implications for elliptic functions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses frustration in finding a holomorphic map from C/(Z+iZ) to itself and questions whether such a function must be doubly periodic and if all elliptic functions are meromorphic but not holomorphic.
  • Another participant suggests the identity function as a potential solution, prompting further discussion on its validity.
  • A different participant argues against the identity function, proposing the need for a function that satisfies f(0)=0, considering piecewise functions or rotations.
  • Another participant questions the mapping z-->2z as a valid function that maps Z+iZ into itself.
  • A participant acknowledges that since the function maps from Z+iZ into itself, it must be holomorphic and doubly periodic, expressing surprise at the simplicity of this condition.
  • One participant notes that for something 'interesting', elliptic functions or doubly periodic functions are necessary, while also acknowledging simpler functions exist.
  • A participant introduces the concept of group homomorphisms, suggesting that any group map from C to C that takes Z+iZ to itself should be considered.
  • Another participant describes a holomorphic map f:C/Z+iZ-->C/Z+iZ and derives properties indicating that such a map is periodic and linear, concluding that f must take the form f(z) = ax for some a in C.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of the functions in question, with no consensus reached on the specific forms or properties of the holomorphic maps or their relationship to elliptic functions. Multiple competing views remain regarding the conditions and characteristics of these functions.

Contextual Notes

Participants discuss the implications of periodicity and the nature of holomorphic versus elliptic functions, but the discussion includes unresolved assumptions about the definitions and properties of these functions.

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grrr, so annoyed, can't see the wood from the trees on this problem!
I'm trying to get a holomorphic map from C/(Z+iZ) -> C/(Z+iZ) where C=complex numbers and Z=integers.
Does this function have to be doubly periodic?
Are doubly periodic functions the same as elliptic functions?
Are all elliptic functions meromorpic but not holomorphic in which case I'm obviously not looking for an elliptic function!
Please Help
 
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what is wrong with the identity function?
 
It Can't be the Identity, must be something else with f(0)=0
I've been thinking of mayb a piecewise function involving the Weirestrass P function... or a rotation... I just can't see where I'm working in my head!
 
What's wrong with z-->2z? It just needs to be some function that maps Z+iZ into itself.
 
Ah, ok, sorry, I was looking for something that was doubly periodic, but since the function is going form Z+iZ into itself, that condition will automatically be satisfied?! And that is Holomorphic too.
It just seems too simple!
 
If you want something 'interesting' then you will need elliptic functions, or doubly periodic ones, for sure - but there are simple ones too.
 
i think these are actually all group homomorphisms, so think in those terms, i.e. any group map C-->C that takes Z+iZ to itself.

i fact the map C-->C is complex linear I believe.

An elliptic function is a holomorphic map from C/Z+iZ-->P where P is the projective line C U {pt}.

they form a field. the holomorphic maps from the torus to itself form a ring, and of course the units in that ring, the automorphisms of the torus, form a group. this group may be always as simple as Z/2Z/, Z/4Z, or z/6Z.
 
Last edited:
a holomorphic map f:C/Z+iZ-->C/Z+iZ, defines a holomorphic map g(z) =
f(z)-f(z+i) with values in the discrete set Z+iZ, hence g is constant.

then g' is zero, so f is periodic with period i, and simiklarly 1.

then f' is bounded hence constant, so f is linear and since f(0) = 0, f(z) = ax for some a in C.
 

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