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Mar
18
comment Graphs cospectral with Cayley graphs
regarding circulants, the first obvious case to try is the graphs with Paley graph parameters (29,14,6,7) on 29 vertices. If anyone cares, these graphs are given here maths.gla.ac.uk/~es/SRGs/29-14-6-7 (converting them into Sage-readable format would be great...)
Mar
18
revised Graphs cospectral with Cayley graphs
english
Mar
18
comment Graphs cospectral with Cayley graphs
no, I don't, I just don't know how to see an example quickly. While for the example I provide it is trivial.
Mar
18
answered Graphs cospectral with Cayley graphs
Mar
10
comment spectrum of Hadamard matrices
in general, one cannot hope for a very nice answer, as one can multiply $H$ by an arbitrary $\pm 1$-permutation matrix, this does not break Hadamard property, but does change eigenvalues.
Mar
10
revised spectrum of Hadamard matrices
improved the answer, more proved
Mar
10
comment spectrum of Hadamard matrices
well, see my edit...
Mar
10
revised spectrum of Hadamard matrices
improved the answer
Mar
10
reviewed Approve An inequality with spherical triangles
Mar
10
answered spectrum of Hadamard matrices
Mar
9
comment What does “game theory” cover and how should it be called?
Historically, game theory has its roots in economics, and that's the area you call "narrow" for some reason. en.wikipedia.org/wiki/Theory_of_Games_and_Economic_Behavior was published in 1944, and most of the topics you mention in the beginning of your question have little to do with this area, it's simply something quite different.
Mar
9
comment Simplicity of $A_n.$
compute the character table, and see that only the trivial character has a kernel.
Mar
8
answered Relationship of Weisfeiler-Lehman algorithm to weak isomorphism of coherent algebras
Mar
5
comment when is the independence number of a graph equals the clique cover number
fort such graphs computing $\alpha(G)$ will be easy, as it's Lovasz $\theta(G)$ (or of the complement of $G$, depending upon its definition.
Mar
5
comment a sum of ratios of quadratic forms
are your $y_k$ and $x_k$ constants vectors? If yes, it's not clear why you cannot rewrite your $f$ as a ratio of 2 polynomials in $A$. If no, why does $f$ depend on $A$ alone?
Mar
5
comment Real square roots of symmetric matrices
Do you need $S$ real, or $S^2$ real suffices?
Mar
3
comment Hypergeometric function asymptotics
wait, isn't your function a polynomial of degree $n-1$? For small $x$ only linear term matters...
Mar
3
comment Hypergeometric function asymptotics
typically one would take an integral representation of the function, and use a method for integral asymptotics. E.g. if you use Euler integral representation for $_2 F_1(c-a,...;x)$ you'd expand the term $(1-xt)^{-c+a}$ into a series and take the biggest terms to get an asymptotic expansion by integration.
Mar
3
comment Corresponding analogy for local compactness in algebraic geometry?
in real algebraic geometry, the analog of compactness is usually closedness+boundedness...
Feb
25
comment More general than semidefinite program?
speaking about complexity, for SDPs in general is it not known, and so one has to tread carefully here.