Math 202B: Applied Algebra II
Winter 2018

Instructor: Brendon Rhoades
Instructor's Email: bprhoades (at) math.ucsd.edu
Instructor's Office: 7250 APM
Instructor's Office Hours: By appointment (after class works well)
Lecture Time: 1:00-1:50pm MWF
Lecture Room: 5402 APM
TA: Dun Qiu
TA's Email: duqiu (at) ucsd.edu
TA's Office: E106 SDSC
Final Exam Time: Friday, 3/23/2018, 11:30am-2:29pm
Final Exam Room: 5292 APM

Lectures:

1/8: Section 1.1. The symmetric group S_n. One-line, two-line, cycle notation for permutations. Cycle type. Partitions. Number of permutations with a given cycle type. Conjugacy classes and centralizers. Conjugacy in S_n. The sign of a permutation. Section 1.2. Matrix representations of groups. Examples. Permutation matrices.
1/10: Section 1.2. More examples of matrix representations. Degree 1 representations of C_n over the complex numbers. Section 1.3. G-modules. Examples. Actions of groups on sets; the permutation representaions k[S]. The group algebra. The regular representation. Coset representations k[G/H]. Equivalence of finite-dimensional G-modules and matrix representations. Section 1.4. Submodules. Examples. Irreducibility.
1/12: Section 1.4. Submodules in terms of matrices. G-module homomorphisms. G-module homomorphisms/isomorphisms in terms of matrices. Kernel and image. Section 1.5. Module direct sum. Indecomposability. Complete reducibility. Maschke's Theorem.
1/17: Section 1.5. Matrix version of Maschke's Theorem. Section 1.6. Baby Schur's Lemma. Real Schur's Lemma. Failure of real Schur over R. Section 1.7. End(V) and Com(X). Matrix tensor product. Description of Com(X) as an algebra of matrices.
1/19: Section 1.8. Centers of algebras. Dimension of the center of Com(X). Tensor products of vector spaces. Operation within tensor products. Universal property of tensor products. Bases of tensor products. Induced linear maps between tensor products; connection to tensor products of matrices. If V is a G-module and W is an H-module, the G x H structure on V tensor W. Tensor products of matrix representations.
1/22: More multilinear constructions: symmetric and exterior powers. Section 1.8. Characters of representations/modules. Examples. Class functions.
1/24: G-invariant inner products. Unitary representations. Section 1.9. Inner product on class functions. Character Orthogonality of the First Kind. Corollaries: two G-modules V and W are isomorphic iff they have the same character. Formula for a character inner product with itself. Section 1.10. Decomposition of the group algebra C[G] into irreducible representations.
1/26: More on C[G]. The number of irreducible characters of G equals the number of conjugacy classes of G. Character tables. Character orthogonality of the second kind. Character tables of S_3, C_4, S_4.
1/29: Section 1.11. Representations of product groups G x H via tensor products. Section 1.12. Induction and restriction of modules. Induction and restriction of characters. Induction via tensor products.
1/31: The coset representation C[G/H] as an induced trivial representation. Frobenius reciprocity on class functions. The character table of D_7. Section 2.1. Partitions, tableaux, and tabloids. The tabloid module M^{lambda}.
2/2: Section 2.1. Young subgroups. The M^{lambda} as induced modules. Section 2.2. Dominance order on partitions. The Dominance Lemma. Section 2.3. The row and column groups R_T and C_T of a tableau T. Young antisymmetrizers kappa_T and polytabloids e_T. Definition of the modules S^{lambda}. Proof that S^{lambda} is closed under the action of S_n. Examples of S^{lambda} when lambda = (n) or (1^n).
2/5: Section 2.4. Inner product on M^{lambda}. Sign lemma. Antisymmetrizer version of Dominance Lemma. Submodule Theorem. The S^{lambda} are irreducible. If lambda and mu are different partitions of n, S^{lambda} and S^{mu} are non-isomorphic. Decomposition of M^{mu} into S^{lambda}'s. Section 2.5. Standard Young tableaux.
2/7: No class. Prof. Rhoades is in LA.
2/9: Section 2.5. Compositions. Dominance order on compositions. Dominance order on tabloids. Proof that the standard polytabloids are linearly independent. Section 2.6. Garnir elements.
2/12: Section 2.6. Proof that the standard polytabloids form a basis for S^{lambda}. Section 2.7. Young's Natural Representation. Section 2.8. Branching rule for symmetric groups. Branching rules for other towers of algebraic objects (e.g. Temperley-Lieb algebras).
2/14: Section 2.8. Proof of the branching rule for symmetric groups. Section 2.9-11. Semistandard tableaux: shape/content. Statement of Young's Rule. Special cases. 2/16: Section 4.1. Ordinary generating functions. Euler's formula. Odd = distinct theorem. Section 4.3. The monomial symmetric functions. The ring of symmetric functions. Power sum, elementary, and homogeneous symmetric functions.


Homework Assignments:

Homework 1, due 1/19/2018.
Homework 2, due 2/2/2018.
Homework 3, due 2/16/2018.