bio  website  

location  
age  
visits  member for  3 years 
seen  1 hour ago  
stats  profile views  314 
1h

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 WeylHeisenberg 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 selfadjoint 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). 