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Apr
30
comment Formula for negative polylogarithms
Does this help? landsburg.com/query.pdf
Apr
26
awarded  Custodian
Apr
25
comment Encoding vectors of size $n$ in matrices which less than $2n$ rows
In view of the OP's evasive responses to further comments on Bob Terrell's answer, I will certainly not be changing my close vote.
Apr
25
comment Encoding vectors of size $n$ in matrices which less than $2n$ rows
@user90628 : I lost you at "It must be done".
Apr
25
comment Encoding vectors of size $n$ in matrices which less than $2n$ rows
This appears (from the response to my comment on Bob Terell's answer) to be a homework problem. I am downvoting and voting to close pending a more satisfactory response to that comment.
Apr
25
comment Encoding vectors of size $n$ in matrices which less than $2n$ rows
@user90628 : i don't understand this at all. What defines the problem? Why don't you want to change the way the product is computed?
Apr
25
comment Encoding vectors of size $n$ in matrices which less than $2n$ rows
@user90628 : Why can't you use the max operator?
Apr
16
comment Generalization of the fiber changing trick for principal bundles?
Locally, $E\approx B\times G$ so locally $E\times_GF\approx B\times (G\times_G F)$ .
Apr
16
awarded  Good Answer
Apr
3
awarded  Good Answer
Apr
1
awarded  Nice Answer
Apr
1
comment Examples of math hoaxes/interesting jokes published on April Fool's day?
@quid (and KConrad): My apologies. I'd quite overlooked the comment.
Apr
1
answered Examples of math hoaxes/interesting jokes published on April Fool's day?
Mar
9
comment Are submodules of free modules free?
Onay oremay ommentscay, easeplay.
Feb
17
comment Rings such that all quotients by prime ideals are PIDs?
@quid: Thanks! $\phantom{xxxxxxxxxxxxxx}$
Feb
17
comment Rings such that all quotients by prime ideals are PIDs?
What does one-and-a-half generated mean?
Feb
16
revised Source and context of $\frac{22}{7} - \pi = \int_0^1 (x-x^2)^4 dx/(1+x^2)$?
Changed $-1$ to $-2$. (I.e. corrected minor typo)
Feb
12
comment if 0→A→A⊕B→B→0 is an exact sequence of finitely generated modules over a commutative Noetherian ring, then the exact sequence does split
See my answer here: mathoverflow.net/questions/167701/…
Feb
8
comment Grothendieck, A Place to Begin
I mostly agree with Joe Silverman. You certainly need some commutative algebra first. But I'd start with Mumford's red book rather than Hartshorne. The first part is a very clear presentation of a (somewhat) more classical approach so you understand what schemes are intended to generalize, and the second part is a very clear presentation of scheme theory with emphasis on why it's the right generalization. There's no cohomology, but first things should come first.
Jan
28
comment If $A$ is the ring of continuous functions on a genus $g$ surface, can the genus of $X$ be seen by simple algebra in $A$?
Given the ring $A$, one recovers the space $X$ as the MaxSpec of $A$, and then you can compute the genus (or any other topological invariant) of $X$ any way you like --- for example, via Cech cohomology. The two steps --- going from $A$ to $X$ and going from $X$ to its genus --- are easily described, so it's easy to describe the composition. "Easily described" is not the same thing as "transparent", but I don't see a reason to expect transparency.