bio | website | cs.ox.ac.uk/people/… |
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location | Oxford, United Kingdom | |
age | 51 | |
visits | member for | 4 years |
seen | 23 hours ago | |
stats | profile views | 1,830 |
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? |