Arnold Neumaier
Reputation
606
Top tag
Next privilege 1,000 Rep.
Create tags
3 14
Impact
~7k people reached

 Apr24 comment Why do Integer Relation Algorithms (e.g. PSLQ) not solve the subset sum problem? @pyramids: 1000 x+ 1001 y = 1 has inifintely many integer solutions but no 0,1 solutions. But even if an equation has a 0,1 solution, why do you expect that an algorithm for finding one of the infinitely many integer solutions should always produce the 01 solution eceot in rare cases?? Apr24 comment Why do Integer Relation Algorithms (e.g. PSLQ) not solve the subset sum problem? @pyramids: An algorithm for solving the integer constrained problem in polynomial time will just find some integer relation. This is very unlikely to be a (0,1) solution (which might not even exist). It cannot get stuck since it is not based on enumerating near solutions. Dec2 comment classical solutions of PDE with mixed boundary conditions Thanks. These and especially their reference to Azzam and Kreyszig are very useful! Nov13 comment Eigenvalues of a bipartite graph @Shahab: It implies that $k|x|=A|x|$. For if this fails then there is strict inequality in at least one component, and multiplication by $u^T>0$ gives a strict inequality, contradiction. Nov9 comment Spectrum of a Block Matrix @Timothy: intuitively: Draw a graph of the corresponding quadratic functions and you'll see where the inequalities hold. - formally: complete the squares, take square roots, and discard the signs not compatible with the case. Nov7 comment Spectrum of a Block Matrix What is your motivation for this conjecture? Nov6 comment Number of local maxima of a function @EwanDelanoy: $F(x)=c$ is the quotient of two polynomials of degree $2k$. So my original $2k-1$ was one off. I corrected the mistake. Jul28 comment recovering a representation from its character @JackSchmidt: Thanks. At the moment, this is more than enough for the finite case. Jul28 comment recovering a representation from its character @JackSchmidt: I am actually not interested in a computer program but in the conceptual ideas behind such an algorithm. So a reference to the original papers would be a useful answer. Jul24 comment Weyl's unitarity trick @QiaochuYuan: At Wikipedia, there is an explicit reference to a paper by Hurwitz but none to Weyl, though his name is mentioned. Jul21 comment Intertwiner in german? google books says that it is not avialable to me for viewing. Could you please give the page number? Jul18 comment Intertwiner in german? It is not enough to find possible translations; since the concept is old one also needs references for actual usage in this context. (Verschlingung sounds more like braiding, which has a very different meaning in group theory.) Jul18 comment Intertwiner in german? @AsafKaragila: Milne forgot to add explanatory notes to the 11th tip. German is not a bad languague for expressing mathematics. Jul18 comment Intertwiner in german? I had done just that before posting the question, but I would have liked to have a single word translation rather than 9 syllables. - Would the term ''äquivariante Abbildung'' also be appropriate for intertwiners between representations of an algebra? Jul6 comment Infinite-dimensional translation-invariant measure I am interested in an infinite-dimensional space with a definite inner product but not necessarily closed in the corresponding topology. Thus it need not be a Hilbert space. May24 comment classical solutions of PDE with mixed boundary conditions Thanks. I hadn't realize before that the pure Neumann case is in Gilbarg/Trudinger which I generally know quite well. I still hope to get info on the mixed case from somewhere.... Mar22 comment Special solution of Helmholtz equation Thanks. This construction is good enough for me. Mar21 comment Special solution of Helmholtz equation But doesn't the differential equation have to hold only in the interior? Wouldn't your statment just mean that the second derivative cannot be continous at the corners?