What is the Definition of an Affine Hypersurface?

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Discussion Overview

The discussion revolves around the definition of an affine hypersurface, exploring both algebraic and geometric perspectives. Participants seek clarity on the concept, particularly in the context of algebraic geometry and its implications in various dimensions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks for a definition of an affine hypersurface, expressing uncertainty.
  • Another participant suggests that a hypersurface is the set of zero points of a polynomial, providing a mathematical representation.
  • A different participant defines an affine hypersurface as a flat hypersurface, noting that in higher dimensions, it corresponds to a hyper-plane.
  • One participant requests more context to better understand the question posed.
  • A later reply clarifies that in algebraic geometry, an affine hypersurface does not need to be defined by a linear polynomial and can be described as a closed subset of codimension 1 in an affine space.
  • This geometric definition emphasizes that an affine hypersurface is generated by a single polynomial, with some participants noting the distinction between irreducible sets and hyperplanes.

Areas of Agreement / Disagreement

Participants express varying definitions and understandings of affine hypersurfaces, indicating that multiple competing views remain without a consensus on a singular definition.

Contextual Notes

There are limitations regarding the assumptions made about the polynomial's properties and the definitions of terms like "irreducible" and "affine space," which may affect the clarity of the discussion.

Ms Mrmr
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what is affine hypersurface :(

Hi all >>
:blushing:

please i want answer about defnition of affine hypersurface ??

thank u :smile:
 
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If I'm not mistaken, then a hypersurface is simply the set of zero points of a polynomial. Thus if P is a polynomial, then the hypersurface defined by P is

\{(x_1,...,x_n)\in k^n~\vert~P(x_1,...,x_n)=0\}

Is this what you meant??
 


An "affine" hypersurface is a flat hypersurface. In one-dimension, that is line, in two-dimensions, it is a plane, in higher dimensions, a hyper-plane. That means that the polynomial, P, that micromass refers to as defining a hypersurface is linear.
 


More context for the question would be nice.
 


micromass thank u but I want the geometry definitoin for affine hypersurface :smile:


HallsofIvy thank u , ur definition is good but pleas i want More detailed about it . :shy:


Hurkyl , sorry , i tierd to explanation my question but i am not speak good english :smile:


thank u all
 


In algebraic geometry an affine hypersurface is excactly what micromass said. There are no restrictions on the polynomial in this context, which means it doesn't need to be linear.

A geometric definition of a affine hypersurface in algebraic geometry could be "a closed subset of codimension 1 of an affine space". (an affine space is normally k^n, where k is algebraically closed field in the zariski-topology, or some subset of this if you want more generality) In other words it is a closed subset of an affine space with dimension one less than the affine space itself. Intuitively you can imagine a 2-dimensional surface (such as a plane, a sphere, a plane intersecting a sphere etc.. in euclidean 3-space). This means it is generated by a single polynomial. Sometimes a hypersurface refers to such an irreducible set (which is what I've seen, but I will not insist on this), which means that the generating polynomial needs to be irreducible.

Hypersurfaces generated by a linear polynomial are generally called hyperplanes (and specifically lines if the dimension is 1).
 
Last edited:


Jarle thank you very much :smile:
 

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