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comment How to solve such an optimization problem
@peng : If the optimal values of $x_i$ take only K different values, then these values are the Fekete points, because then all non zero terms in the sum are maximized.
Aug
19
awarded  Yearling
Aug
1
comment Finite subgroups (lattices) in the large N limit of SU(N)
A larger finite subgroup than the Weyl-Heisenberg group is its normalizer, see e.g. arxiv.org/abs/1003.3591v2 .
Jul
2
awarded  Curious
Jun
12
comment Method to Generate Random Mutually Orthogonal Unitary Matrices
What exactly is the probability measure you want to simulate ?
Jun
11
comment Computing $\int_0^T e^{itA}Be^{-itA} dt$ without an infinite series
Why so complicated ? Simply diagonalize A, as mentioned by Christian Remling.
May
25
awarded  Editor
May
25
revised Is this functional maximized by SU(2) coherent states?
added 6 characters in body
May
25
asked Is this functional maximized by SU(2) coherent states?
May
22
comment eigenvalues of product of many symmetric positive definite matrices
if d is even then all eigenvalues might be negative : According to the theorem of Ballantine (projecteuclid.org/download/pdf_1/euclid.pjm/1102991595) we can write minus identity as a product of positive definite real matrices, since it has positive determinant.
May
22
comment eigenvalues of product of many symmetric positive definite matrices
Wurlitzer : to "negative definite" : Not true, e.g. for x = 2, there is 1 positive and 1 negative eigenvalue, so its neither positive nor negative definite.
May
20
comment Absolute value inequality for complex numbers
@Deane Yang : Doesn't work because for the 3 distinct third roots of unity also equality holds.
May
20
comment Absolute value inequality for complex numbers
If we choose the third roots of unity for a,b,c then equality holds.
May
18
comment Solvability of a Fredholm system in $L^2$
@fedja : So the answer is yes : all eigenfunctions with non zero eigenvalue of the integral operator restricted to the subspace of odd functions are solutions.
Apr
1
comment A.C. spectrum of the non additive perturbation BAB of a self-adjoint operator A where B is strictly positive
Is this related to anderson localisation ?
Mar
6
answered Does positivity preserve compactness?
Dec
3
comment Fixed point theorems and equiangular lines
@Peter: Can you formulate the conjecture as a fixed point problem ?
Nov
1
comment What is entropy, really?
@Marek : The entropy of a black holes is not zero. Instead it is much greater than the entropy of the star that collapsed to the black hole.
Nov
1
comment What is entropy, really?
Entropy measures our ignorance : It is the logarithm of the phase space volume of macroscopically indistinguishable states. See Roger Penrose, The road to reality, chapter 27.3 .
Oct
16
comment Set of physical states of FQHE on closed Riemann surface = ?
to "set of possible states of that physical system" : That's just the Hilbert space of the quantum system. Furthermore there is no phase transition in FQHE / IQHE (in contrast to superconductivity).