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location Oxford, United Kingdom
age 51
visits member for 4 years, 4 months
seen 7 hours ago

Jan
30
comment How was Christoffel a 'whimsical eccentric'?
'die Theorie der Formen' probably meant algebraic geometry
Jan
25
comment Cholesky decomposition of a positive semi-definite
how about ldl ?
Jan
22
comment Binomial Identity
see e.g. the book "A=B": math.upenn.edu/~wilf/AeqB.html
Jan
22
comment A determinant problem with symmetric PSD matrices
it is not advised to use lower case letters to denote matrices, especially if you use $I$ to denote the identity matrix, unless you want to confuse readers...
Jan
22
comment Cholesky decomposition of a positive semi-definite
en.m.wikipedia.org/wiki/Cholesky_decomposition has a proof that yes, indeed, it is correct, a p.s.d. R will have a Cholesky decomposition.
Jan
21
comment A determinant problem with symmetric PSD matrices
$v_i v_i^H$ is of rank 1, i.e. all its eigenvalues except one are 0.
Jan
21
comment Cholesky decomposition of a positive semi-definite
Do you mean to ask why R has a Cholesky decomposition if and only if R is positive semidefinite?
Jan
20
comment Cholesky decomposition of a positive semi-definite
"that how a positive semi-definite be done for Cholesky decomposition"??? What do you mean? English, please...
Jan
3
comment Can you efficiently solve a system of quadratic multivariate polynomials?
it is well-known that one can find representatives of connected components of real algebraic sets in $\mathbb{R}^n$ encoded by degree $d$ polynomials in $O(d)^{O(n)}$ ring operations. And $n$ in the exponent is not avoidable, generally speaking, unless P=NP.
Jan
3
answered Can you efficiently solve a system of quadratic multivariate polynomials?
Jan
1
answered Teaching homology via everyday examples
Dec
7
comment Fubini for distributions which are not measures?
Do you mean to say we should look at the pushforward of $\Phi$ being a restriction to a sufficiently long interval in the subspace orthogonal to the (conjectural) support of $\mu$, and get a distribution with finite support?
Dec
6
comment Fubini for distributions which are not measures?
Well, $F(u,v)$ is defined as above. It's an attempt to push a (combinatorial) setup which under some assumption was giving us measures, and everything was easy. Now we are trying to extend it further, and have this weirdness...
Dec
6
revised Fubini for distributions which are not measures?
positive is not the right term here
Dec
6
asked Fubini for distributions which are not measures?
Nov
29
comment About large z behavior of hypergeometric function $_2F_1(1/2,1/2,1;z)$
Did you try looking at standard sources on asymptotic expansions of integrals? It's probably doable by some standard technique.
Nov
26
awarded  Yearling
Oct
29
awarded  Popular Question
Oct
11
comment How close to platonic can a non-platonic planar graph be?
You get quite a bit of constraints from Euler formula $v-e+f=2$: your graph is regular, i.e. $2e=vk$, and the $f-1$ faces are $\ell$-gonal, while the remaining face is $\ell'$-gonal. So this gives $2e=(f-1)\ell+\ell'$. Finally, don't forget topology, which forbids $\ell$ greater than 5...
Oct
2
awarded  Caucus