4,249 reputation
724
bio website cs.ox.ac.uk/people/…
location Oxford, United Kingdom
age 51
visits member for 4 years
seen 3 mins ago

Aug
30
revised On the positivity of matrices
added 285 characters in body
Aug
30
revised On the positivity of matrices
edited tags
Aug
30
revised On the positivity of matrices
added 204 characters in body
Aug
30
comment On the positivity of matrices
IIRC, the minimal size for counterexample is $n=5$.
Aug
30
comment On the positivity of matrices
This computational technique is called semi-definite programming.
Aug
30
answered On the positivity of matrices
Aug
30
reviewed Approve Is there an analog of the Barratt-Eccles construction for group-like E_∞-spaces and E_∞-ring spaces?
Aug
25
reviewed Approve Largest eigenvalue adjacency matrix-link deletion
Aug
25
answered Largest eigenvalue adjacency matrix-link deletion
Aug
25
comment Invariant planes of a nilpotent matrix with two Jordan blocks of size two
The 2-dimensional subspaces are parametrised by the points on a quadric $Q$ in $P^5$, via Plucker coordinates. You can write down how $N$ acts there, and take the fixed vectors of linear map which satisfy the quadratic relation defining $Q$. Thus you will have them parametrised by the intersection of $Q$ and the linear subspace of fixed points.
Aug
24
answered Real solutions for systems of monomial equations
Aug
24
comment Real solutions for systems of monomial equations
this is a particular case of a problem involving binomial ideals; the latter are quite well-studied, in the context of toric varieties.
Aug
18
comment How to prove a Proposition of Rouquier?
how can it be so that some statements in the text indicate that it's not clear how to prove some other statement in the same text?!
Aug
18
comment What is the minimal girth of a cayley graph for Alt(n) in which the girth relator is not a proper power?
6? Why? Why not 42? :)
Aug
18
comment What is the minimal girth of a cayley graph for Alt(n) in which the girth relator is not a proper power?
from topology point of view, you might want to disregard length 2 loops.
Aug
18
reviewed Approve Kaplansky's idempotent conjecture for Thompson's group F
Aug
13
comment Linkage between homotopy equivalence and identification of algorithms
this is called "univalent foundations of mathematics", see e.g. homotopytypetheory.org
Aug
8
answered Possible degrees of faithful projective representations of $\mathrm{PSL}(k,q)$ and $\mathrm{Sp}(2k,q)$ over complex numbers
Aug
8
comment Possible degrees of faithful projective representations of $\mathrm{PSL}(k,q)$ and $\mathrm{Sp}(2k,q)$ over complex numbers
The poster most probably doesn't have access to Magma. (well, the same computations can be done in GAP (gap-system.org), which is free...)
Aug
6
comment When polynomial GI implies polynomial (edge) colored GI?
other questions are harder :)