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The Lumenary
研究生一年级Geometry & Topology计划中

Algebraic geometry

Affine and projective varieties, the Zariski topology, coordinate rings, morphisms and rational maps, dimension, and a first look at sheaves and schemes.

math.geom.algebraic-geometry

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前置知识

46 项必需的前置知识(一直追溯到底)

你将学会

  • Pass between ideals and affine varieties using the Nullstellensatz.
  • Work with projective varieties, homogeneous coordinates and Bézout's theorem for plane curves.
  • Explain why schemes generalise varieties, using Spec of a ring and its structure sheaf.

定义

  • An affine algebraic set is the common zero set in kⁿ of a set of polynomials; a variety is often required in addition to be irreducible.
  • The Zariski topology has the algebraic sets as its closed sets.
  • Spec R, with the Zariski topology and its structure sheaf, is an affine scheme.

定理

  • Over an algebraically closed field, radical ideals of k[x₁, …, xₙ] correspond bijectively, reversing inclusion, to algebraic subsets of kⁿ.
  • Bézout: over an algebraically closed field, two projective plane curves of degrees d and e with no common component meet in exactly de points counted with multiplicity.
  • Over an algebraically closed field, the category of affine varieties is equivalent to the opposite of the category of finitely generated reduced k-algebras.

常见误解

  • Thinking the Zariski topology is Hausdorff; on any infinite irreducible variety it is not.
  • Treating a variety as just a set of points; its coordinate ring carries the structure.

可选发现

延伸阅读

  • Robin Hartshorne, Algebraic Geometry (1977)
  • David Cox, John Little and Donal O'Shea, Ideals, Varieties, and Algorithms
  • Igor R. Shafarevich, Basic Algebraic Geometry