Math 669: Cluster algebras
Winter 2018
Course meets: Tuesday and Thursday 1:10-2:30 in 3866 East Hall.
Instructor:
Sergey Fomin, 4868 East Hall, 764-6297,
fomin@umich.edu
Course homepage: http://www.math.lsa.umich.edu/~fomin/669w18.html
Level: introductory graduate.
Prerequisites: none (for graduate students).
Synopsis:
Cluster
algebras
are a class of commutative rings constructed via a recursive
combinatorial process of "seed mutations." They arise in a variety
of algebraic and geometric contexts including representation theory
of Lie groups, Teichmüller theory, discrete integrable systems,
classical invariant theory, and quiver representations. This course
will provide an elementary introduction to the basic notions and
results of the theory of cluster algebras, and present some of its
most accessible applications. Combinatorial aspects will be
emphasized throughout. No special background in commutative algebra,
representation theory, or combinatorics is required.
Main reference:
Additional references:
Helpful links:
Lecture topics:
- Motivating examples: Grassmannians of planes, basic affine
spaces.
[Slides]
- Quiver mutations. Examples: triangulations, wiring diagrams.
[Sections 2.1-2.4]
- Plabic graphs. [arXiv:1711.10598, Section 7]
- Mutation equivalence [Section 2.6]. Triangulated surfaces
[arXiv:math/0608367, Sections 2, 4].
- Finite mutation type [arXiv:0811.1703].
Restriction and freezing for quivers [Sections 4.1-4.2].
- Matrix mutations [Sections 2.7-2.8].
- Folding and unfolding [Section 4.4].
- Cluster algebras of geometric type [Section 3.1].
- Cluster algebras of rank 2 [Section 3.2]. The Laurent Phenomenon
(easy cases).
- The Laurent Phenomenon [Section 3.3].
- Somos sequences [Section 3.4]. Y-patterns [Section 3.5].
- Point configurations on a projective line.
The pentagram map [Section 3.5].
- Tropical semifields [Section 3.6].
Rescaling [Section 4.3].
- Seed patterns of finite type. Rank 2 [Section 5.1].
Cartan matrices and Dynkin diagrams [Section 5.2].
- Finite type classification (statement) [Section 5.2]. Seed patterns of
type A_{n} [Section 5.3].
- Seed patterns of type D_{n} [Section 5.4].
- Seed patterns of types B_{n} and
C_{n} [Section 5.5].
Seed patterns of exceptional types
[Sections 5.6-5.7].
- Guest lecture #1 by D. Thurston: Cluster algebras from
surfaces: hyperbolic geometry.
- Guest lecture #2 by D. Thurston: Cluster algebras from
surfaces: representation theory.
- Cluster algebras from surfaces: recapitulation.
Seed patterns of finite type: enumeration [Sections 5.8-5.9].
- 2-finite exchange matrices. Quasi-Cartan companions [Sections
5.10-5.11]. Cluster structures in commutative rings.
- The Starfish Lemma.
- Cluster structures for base affine spaces.
- Cluster structures in C[SL_{k}].
Cluster structures in Grassmannians.
- Zamolodchikov periodicity
(type A_{k}×A_{l}).
Cluster structures in rings of invariants.
- Guest lecture #3 by A. Leaf:
Cluster algebras and dimer models.