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

location  Ann Arbor  
age  34  
visits  member for  5 years, 5 months 
seen  12 hours ago  
stats  profile views  32,786 
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.
2d

awarded  Nice Answer 
2d

answered  Polyhedra containing hexagones only 
2d

comment 
Computing $\prod_p(\frac{p^21}{p^2+1})$ without the zeta function?
@VladimirDotsenko Yes it is. That's why I didn't wind up sending this anywhere. See testcase's answer below. 
Mar 27 
answered  Are there any Algebraic Geometry Theorems that were proved using Combinatorics? 
Mar 25 
accepted  Are there any natural differential operators besides $d$? 
Mar 25 
comment 
Are there any natural differential operators besides $d$?
Following links from your paper, the answer to the specific question I asked is Theorem 5.7 in "Natural vector bundles and natural differential operators" by Terng jstor.org/stable/2373910, and appears to have been proved around the same time by several Russian authors whom I haven't read yet. Thanks for the reference! I definitely appreciate your point about how the problem becomes different with only diffeomorphisms in the picture  and much harder. 
Mar 25 
comment 
Are there any natural differential operators besides $d$?
I'm reading the paper you linked now. It seemed to me that any natural linear operator would be the direct sum of its projections onto the Schur factors, so the Schur case does everything. But maybe it will be clear what I am missing after I finish reading the article you linked. 
Mar 25 
revised 
Are there any natural differential operators besides $d$?
added 5 characters in body 
Mar 25 
comment 
Are there any natural differential operators besides $d$?
A bigger problem for the specific formalism I set up is that vector fields are sections of the dual of $T^{\ast} X$, and dual is not a Schur functor (it is contravariant, not covariant!). This is why you have to restrict to diffeomorphisms when working with vector fields. 
Mar 25 
comment 
Are there any natural differential operators besides $d$?
@VladimirDotsenko Couldn't you make them arguments of one argument though, by thinking of them as a map from $(\mbox{vector fields}) \otimes (\mbox{whatever}) \to \mbox{whatever}$? Contractions don't obey Liebnitz in the sense I wrote, but there might be something you could build from Lie derivatives. 
Mar 25 
awarded  Nice Question 
Mar 24 
awarded  Good Answer 
Mar 22 
asked  Are there any natural differential operators besides $d$? 
Mar 13 
comment 
Is there a method to simultaneously blockdiagonalize a set of group matrices?
Wait, is this a group in characteristic zero? Then I would compute the center of this group algebra (linear algebra) and diagonalize the central elements (since they commute). 
Mar 13 
comment 
Is there a method to simultaneously blockdiagonalize a set of group matrices?
See math.stackexchange.com/a/185001/448 . If someone reading this knows a better place to point people than my answers, please do so! 
Mar 13 
comment 
Estimate self crossings of a curve parameterized by a trigonometric polynomial
Related (but also unanswered) mathoverflow.net/questions/90856 
Mar 12 
comment 
Examples of eventual counterexamples
Sorry, comment two earlier should read $\sqrt{(10^n+1) m}$, not $\sqrt{10^n+1}$. 
Mar 12 
comment 
Examples of eventual counterexamples
For example,$13^210^{39}+1$ and $384615384615384615384615384615384615385^2 = (147928994082840236686390532544378698225)*(10^{39}+1)$, reflecting that $5/13 = 0.384615\cdots$. 
Mar 12 
comment 
Examples of eventual counterexamples
@DavidMandellFreeman If $(10^n+1) m$ is square for $m<10^n$, then $10^n+1$ must have a square divisor, say $10^n+1 = s^2 t$ and $m = r^2 t$. Then $\sqrt{10^n+1} = rst \approx 10^n (r/s)$. So the RHS will look very close to a decimal expansion of $r/s$. The first nonsquarefree numbers of the form $10^n+1$ are $11^2  10^{11}+1$ and $7^2  10^{21}+1$. If you search further, I'm sure other denominators occur. 
Mar 12 
comment 
Two questions about discriminants of polynomials in Q[x]
@wishcow Oops! Fixed, thanks. 