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Jan
5 |
revised |
Is there a version of Robertson-Seymour's graph minor theorem known to apply to signed graphs?
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Jan
5 |
comment |
Is there a version of Robertson-Seymour's graph minor theorem known to apply to signed graphs?
Exactly. @Tony, many thanks for your clarifications and answer. |
Jan
3 |
accepted | Is there a version of Robertson-Seymour's graph minor theorem known to apply to signed graphs? |
Jan
2 |
asked | Is there a version of Robertson-Seymour's graph minor theorem known to apply to signed graphs? |
Jul
10 |
revised |
Convergence rate of iterated nonlinear equations?
fixed small format error |
Jun
19 |
comment |
Reference request for: inverse of a non-singular M-matrix has all elements non-negative?
Fan 1958, Theorem 5' in "Topological proofs for certain theorems on matrices with non-negative elements..." is now the earliest reference I can find. |
Jun
19 |
comment |
Reference request for: inverse of a non-singular M-matrix has all elements non-negative?
Thanks Dmitry. Looking there and the refs given, Fiedler and Ptak 1962 provide a proof without referencing an earlier result, though earlier work by Ostrowski, Fan, Koteljansku and Minkowski are mentioned, and I imagine one of those probably proved this result earlier. |
Jun
19 |
comment |
Reference request for: inverse of a non-singular M-matrix has all elements non-negative?
Sorry, you're right, now fixed. As you say, it's an old topic. The result may be found in several places but I'd like to reference the original result if possible. |
Jun
19 |
revised |
Reference request for: inverse of a non-singular M-matrix has all elements non-negative?
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Jun
18 |
asked | Reference request for: inverse of a non-singular M-matrix has all elements non-negative? |
May
25 |
comment |
Perturbed linear system, particular form
Hi Frederico, I was not familiar with the term but from reading Wikipedia en.wikipedia.org/wiki/Stieltjes_matrix yes - sorry, I have added the important point that we may assume A is positive definite, hence is a Stieltjes matrix (and hence an M-matrix). Are relevant results known for such? Thanks for any help. |
May
25 |
revised |
Perturbed linear system, particular form
clarification |
May
25 |
revised |
Perturbed linear system, particular form
Minor correction |
May
25 |
revised |
Perturbed linear system, particular form
added 7 characters in body |
May
25 |
revised |
Perturbed linear system, particular form
added 29 characters in body |
May
25 |
revised |
Perturbed linear system, particular form
added 45 characters in body |
May
25 |
asked | Perturbed linear system, particular form |
May
24 |
awarded | Tumbleweed |
Jun
19 |
accepted | Lower bound for sum of square root of the degrees of a connected graph |
Jun
10 |
comment |
Lower bound for sum of square root of the degrees of a connected graph
Thanks Gjergji, that's very helpful! Still I wonder if $\left( \sum_{i=1}^n \sqrt d_i \right)^2 \geq kmn$ for some $k$ for all connected simple graphs? Note that for a star graph, which we might suspect is extreme, $k=1$ works. |