David White
Reputation
Next privilege 10,000 Rep.
Access moderator tools
 14h comment Pullback-stable model of fibrewise suspension of fibrations (in simplicial sets, or similar setting) It seems the answer for sSet is here in the comments. The key point is to use the Sing(|-|) adjunction to Top, where all objects are fibrant. The same trick should work for simplicial presheaves with the projective model structure, since fibrancy is detected levelwise. Peter, I think you should write an answer of your own using the comments and then if someone does better give them the bounty. Otherwise give yourself the bounty (if you can). I can't see how to do this in general. Sep 30 comment Given k, what is the minimum n such that n choose n/2 is greater than k? Okay, I wrote out an argument using Newton's method. I was going to post it as an answer, but I guess people felt the question was too elementary. I have to say: it was not too elementary to me, and I'm a pretty active mathematician. In fact, I think this is exactly what MO is supposed to be for. Anyway, thanks Igor for your answer and the pointer to Newton's method, and thanks GH for suggesting the target to approximate. Sep 29 reviewed Approve Dimension of subalgebras of a matrix algebra Sep 29 comment Given k, what is the minimum n such that n choose n/2 is greater than k? Thanks for the answer. I just skimmed through that paper and while it seems to have great asymptotics for ${2n \choose n}$, I could not seem to find much about the inverse of this function (i.e. a bound on $k$ above). Can you see how to use these asymptotics to derive a bound like the one in GH's comment above? Thanks again. Sep 29 comment Given k, what is the minimum n such that n choose n/2 is greater than k? @GHfromMO: could you give a reference for that or sketch an argument? That is probably the answer I'm looking for, but it doesn't appear in either the wikipedia article or Igor's answer Sep 29 comment Given k, what is the minimum n such that n choose n/2 is greater than k? @Boris: Thanks, I'll check that out. Thanks GH for the even more explicit answer. I'm actually kind of happy that there is no exact formula, since I wasted a fair bit of time today trying to find one. Sep 29 comment Given k, what is the minimum n such that n choose n/2 is greater than k? My question might be related to this one here, but again I can't seem to read off a formula from that: mathoverflow.net/questions/132263. At the very least, it seems the question could be reformulated to be about blocks in a maximal packing Sep 29 asked Given k, what is the minimum n such that n choose n/2 is greater than k? Sep 29 revised Pullback-stable model of fibrewise suspension of fibrations (in simplicial sets, or similar setting) edited title Sep 28 comment Basic questions about simplicial commutative rings I don't know of a reference that discusses this. I looked in Weibel's book on homological algebra, but no luck. I checked Hirschhorn too but couldn't find it. At this point, if it's not in Goerss-Schemmerhorn then I'd probably go back to Quillen, or chapter 8 of Jardine's local homotopy theory, or maybe one of the Dwyer-Kan papers. Due to teaching and a visitor to our department I probably won't have a chance to respond again till next weekend, but maybe the references here will help. Sep 28 awarded Nice Answer Sep 26 awarded Necromancer Sep 25 revised Basic questions about simplicial commutative rings deleted 1 character in body Sep 25 reviewed No Action Needed Intertwiners and Clebsch-Gordan coefficients Sep 25 revised Basic questions about simplicial commutative rings added 41 characters in body Sep 25 answered Basic questions about simplicial commutative rings Sep 23 reviewed Approve Integers in Boxes Problem Sep 22 comment Rectifying the definition of a closed category Does this MO thread help? mathoverflow.net/questions/21382/… Sep 21 comment Iterated Homotopy Quotient @Fernando: I don't think it's what Jon means, but your question reminded me of recent work of Farjoun and collaborators. Perhaps those papers can be used to define a good topological notion of the relationship between a group and a normal subgroup. Sep 21 comment What are examples when the equality of some invariants is good enough in algebraic topology? I like the new title much better.