Yibo Gao

Online Learning Seminar in Algebraic Combinatorics.

Fall 2025

We will be reading Speyer's survey for the first half of the semester, followed by some research talks for the second half of the semester.

• Topic: Richardson varieties.
• Time: Friday 9am Beijing time (Thursday 9pm EST).
• Tencent Meeting: 354-6294-8983.
• Recordings: please click on the title below.

Date	Speaker	Topic
Sep 19	Mingzhi Yang	Background on Richardson varieties. Note.
Sep 26	Yiming Chen	Positroids. Note.
Oct 10	Weihong Xu	Bott-Samelson varieties and brick varieties. Note.
Oct 17	Yuhan Jiang	The Deodhar decomposition. Note.
Oct 24	Yuchen Zhu	Total positivity. Note.
Oct 31	Tao Gui	Cohomology rings of Bott-Samelson varieties. Note.
Nov 7	Shiliang Gao	The Plücker algebra. Note.
Nov 14	Hai Zhu	Plabic graphs.
Nov 21	Ming Yao	Bumpless pipe dream fragments -- equivariant geometry of clans.
Nov 28	Rui Xiong	Topology of totally nonnegative flag vaireties.
Dec 5	Neil J. Fan	Cluster structure on the Grassmannian.

Spring 2025

Rui Xiong will be the main lecturer for this semester, partially following his notes.

• Topic: Macdonald Theory.
• Time: Thursday 9am Beijing time (Wednesday 8pm EST).
• Tencent Meeting: 623-4026-3282.
• Recordings: please click on the title below.

Date	Speaker	Topic
Feb 20	Rui Xiong	Hall-Littlewood polynomials, definitions and examples. Note.
Feb 27	Rui Xiong	Applications of Hall-Littlewood polynomials (1). Note.
March 6	Rui Xiong	Applications of Hall-Littlewood polynomials (2). Note.
March 13	Hai Zhu	Combinatorial formula for Kostka-Foulkes polynomials. Note.
March 20	Rui Xiong	Macdonald polynomials, definition and examples (1). Note.
March 27	Rui Xiong	Macdonald polynomials, definition and examples (2). Note.
April 3	Ming Yao	Plethysm, quasi-symmetric functions and superization. Note.
April 10	Rui Xiong	Applications of Macdonald polynomials. Note.
April 17	Dun Qiu	LLT polynomials. Note.
April 24	Peter L. Guo	A combinatorial formula for Macdonald polynomial. Note.