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Nov
30
revised bounding the sum of the entries of the inverse of a 0-1 matrix away from 1?
typos fixed: n->1
Nov
30
comment bounding the sum of the entries of the inverse of a 0-1 matrix away from 1?
Suvrit's suggestion is about the Frobenius norm. The conjecture he states there does not imply mine: indeed, $A^{-1}$ can have negative entries.
Nov
30
comment bounding the sum of the entries of the inverse of a 0-1 matrix away from 1?
@Gerhard, more precisely, the conjecture does not say that always $a\geq 1$. It only says that if $a\geq$ then...
Nov
30
comment bounding the sum of the entries of the inverse of a 0-1 matrix away from 1?
I don't understand this answer. Elkies shows that it is possible that $a$ is exponentially big. I am asking whether $a-1$ can be positive, but exponentially small.
Nov
30
awarded  Enthusiast
Nov
30
asked bounding the sum of the entries of the inverse of a 0-1 matrix away from 1?
Nov
27
comment Graphs with a unique transmission value
@Gordon: you mean strongly regular, I think.
Nov
26
comment theta series of neighbours
welcome to mathoverflow :)
Nov
26
revised theta series of neighbours
typos fixed
Nov
26
awarded  Yearling
Nov
25
accepted lines through A_n reflection arrangement and permutations
Nov
25
comment lines through A_n reflection arrangement and permutations
Thanks, great, that's precisely what we are looking for! (One needs to embed $\ell$ in a plane and obtain an arrangement of lines.) It even answers a more general question than the original.
Nov
25
revised lines through A_n reflection arrangement and permutations
updated and made more precise to address the criticism
Nov
24
comment lines through A_n reflection arrangement and permutations
The question I am struggling a bit to formulate, as I see from responses, is about a combinatorial order being realizable by a geometric construction...
Nov
24
revised lines through A_n reflection arrangement and permutations
rectifucation
Nov
24
comment lines through A_n reflection arrangement and permutations
I don't understand the comment. My $c_t$ is already selected, it is far from $c_0$ in the sense that $\ell$ has to cross all the hyperplanes of the arrangement. E.g. for $n=3$ the cell $c_t$ can chosen to correspond to $\sigma(c_t)=(13)$, where the cell $c_0$, with $\sigma(c_0)=()$, is bounded by hyperplanes $H_{12}$ and $H_{23}$. Actually, if I am not mistaken, one can assume in general that $\sigma(c_t)=(1,n)(2,n-1)(3,n-2)...(i+1,n-i)...$
Nov
24
comment lines through A_n reflection arrangement and permutations
It looks as if you stripped too much. Indeed, your permutation equals (), the trivial permutation, as you can see by multiplying these (2,3)(1,2)(3,0)(2,0)(1,3)(1,0) out. Surely this has nothing to do with being able to get from () to a permutation which is far from it in the combinatorial sense, e.g. in terms of the distance in the Cayley graph of $S_n$ on transpositions.
Nov
24
asked lines through A_n reflection arrangement and permutations
Nov
21
comment A certain type of Quadratic Constrained Quadratic Programming Problem (QCQP)
e.g. if you have BLAS and LAPACK on your system then you can easily use CSDP: coin-or.org/projects/Csdp.xml
Nov
21
comment A certain type of Quadratic Constrained Quadratic Programming Problem (QCQP)
well, if your RT system has an floating point processor, and you can compile C code for it, then you can get some open source SDP solver and use it, why not?