Algebraic varieties

Definition

Algebraic varieties are geometric objects defined as the solution sets of polynomial equations over a given field. They can be classified as affine or projective, depending on whether they reside in affine space or projective space. This concept serves as a bridge between algebra and geometry, allowing for the study of their properties through both algebraic and topological means.

5 Must Know Facts For Your Next Test

1. Algebraic varieties can be classified into two main types: affine varieties, which are defined by polynomial equations in an affine space, and projective varieties, which are defined in projective space using homogeneous polynomials.
2. The solutions of polynomial equations define the points of an algebraic variety, and the structure of these varieties can be studied using coordinate rings derived from those polynomial equations.
3. The Zariski topology is a specific topology used on algebraic varieties where closed sets correspond to the vanishing sets of collections of polynomials.
4. Every algebraic variety can be given the structure of a ringed space, where the stalks at each point correspond to local rings of functions defined on that variety.
5. The study of algebraic varieties includes various dimensions, where the dimension of a variety corresponds to the number of independent variables needed to describe it locally.

Review Questions

• How do affine and projective varieties differ in terms of their definitions and properties?
  • Affine varieties are defined as the solution sets of polynomial equations within an affine space, where the focus is on local coordinates and real-number solutions. In contrast, projective varieties are defined using homogeneous polynomials in projective space, which allows for the consideration of points at infinity. This distinction influences their geometric properties and how they interact with concepts like intersection theory and dimension.
• Discuss how the Zariski topology contributes to our understanding of algebraic varieties and their geometric properties.
  • The Zariski topology provides a way to study algebraic varieties by defining closed sets based on the vanishing loci of polynomial equations. This unique topology allows for the examination of properties like irreducibility and dimension within the context of algebraic geometry. By using this topology, mathematicians can gain insight into the relationships between different varieties and how they can be transformed or intersected.
• Evaluate the role of sheaves in connecting algebraic varieties with ringed spaces and how this impacts their study.
  • Sheaves play a crucial role in bridging algebraic varieties with ringed spaces by allowing local data to be systematically organized. In this framework, each open set of an algebraic variety can be associated with a sheaf of functions, facilitating the study of local properties and global behaviors simultaneously. This connection enhances our understanding of morphisms between varieties and opens pathways to deeper concepts like cohomology and deformation theory, thus enriching the overall landscape of algebraic geometry.

Related terms

Polynomial ring: A ring formed from polynomials with coefficients in a given field, which is fundamental in defining algebraic varieties.

Sheaf:

A tool that associates data to open sets of a topological space, providing a framework to study algebraic varieties in a more structured manner.

Schemes: Generalizations of algebraic varieties that allow for more flexibility by incorporating nilpotent elements, enabling a broader approach to algebraic geometry.