bio  website  math.lsa.umich.edu/~speyer 

location  Ann Arbor  
age  34  
visits  member for  5 years, 1 month 
seen  3 hours ago  
stats  profile views  30,921 
Associate Professor of Mathematics at the University of Michigan. My research interests are in combinatorial algebraic geometry, particularly Schubert calculus, matroids and cluster algebras. I also enjoy thinking about number theory and computational mathematics.
1h

awarded  Nice Question 
6h

asked  A funny factorization of the Jacobian coming from the lines on the Fermat cubic 
7h

comment 
Powers of traces, integrals over spheres and class functions
Its probably worth explicitly pointing out that, if the eigenvalues of $A$ are $\lambda_1$, $\lambda_2$, ..., $\lambda_n$, then $\mathrm{Tr}((A \otimes A \otimes \cdots \otimes A) P_{sym})$ is $\sum_{k_1+\cdots+k_n=k,\ k_i \geq 0} \lambda_1^{k_1} \lambda_2^{k_2} \cdots \lambda_n^{k_n}$. 
7h

answered  Decidable theorem or result that is not weaker than Tarski's theorem 
1d

comment 
Powers of traces, integrals over spheres and class functions
I think your denominator on the $k=3$ expression should be $n^3+3n^2+2n=n(n+1)(n+2)$, not $3n(n+1)$. Up to the question of scaling, it looks like $\alpha_k(A)$ is the trace of $A$ acting on $\mathrm{Sym^k}(V)$. 
1d

comment 
Hirzebruch's motivation of the Todd class
@GHfromMO Thanks for the sign correction. Changed "inverse function theorem" to "holomorphic inverse function theorem". Rouche or the argument principle shows that $h$ exists, but how do you know it is differentiable, let alone holomorphic, if you cite those theorems? 
1d

revised 
Hirzebruch's motivation of the Todd class
deleted 27 characters in body 
1d

answered  Hirzebruch's motivation of the Todd class 
Nov 21 
answered  Can all $L^2$ holomorphic functions on a domain vanish at a particular point? 
Nov 21 
awarded  Nice Answer 
Nov 18 
awarded  Revival 
Nov 18 
revised 
What makes the Cartier operator “tick”?
added 2 characters in body 
Nov 18 
answered  What makes the Cartier operator “tick”? 
Nov 18 
awarded  Nice Answer 
Nov 17 
comment 
How many Pythagorean triples are there in which every member is triangular?
@JeremyRouse I don't want a tag as much as I want someone to ask the question: What is known about algorithms for finding/bounding integral points on K3 surfaces? 
Nov 15 
comment 
Trace map for sepeared morphism of nonsingular varieties
Do I understand correctly that the proof in Zannier would be correct if Zannier imposed that $X$ was nonsingular, not just normal? (And, therefore, Zannier's paper is a correct answer to the stated question.) 
Nov 15 
comment 
Trace map for sepeared morphism of nonsingular varieties
To spell out the counterexample in the paper a bit better, let $\mathrm{char(k)} \neq 0$, let $X' = \mathrm{Spec} k[u,v]$ and let $X = \mathrm{Spec} k[u^2, uv, v^2]$, with the obvious map. Then $Tr(u dv)$ should be $2 u dv$. We have $2 u dv = (u/v) d(v^2) = 2 d(uv)  (v/u) d(u^2)$, so $2 u dv$ is regular on the smooth part of $X$, but it isn't regular at the singular point. 
Nov 15 
awarded  Enlightened 
Nov 15 
awarded  Nice Answer 
Nov 13 
revised 
Two (other) rings…are they isomorphic?
added 627 characters in body 