Arnold Neumaier
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 Jun 28 comment Generalization of De Rham cohomology for spinor fields There is an answer at physicsoverflow.org/32072 May 10 comment rigorous treatment of infinitesimal reparametrizations some answers are at physicsoverflow.org/30865 Apr 24 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?? Apr 24 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. Dec 2 comment classical solutions of PDE with mixed boundary conditions Thanks. These and especially their reference to Azzam and Kreyszig are very useful! Nov 13 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. Nov 9 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. Nov 7 comment Spectrum of a Block Matrix What is your motivation for this conjecture? Nov 6 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. Jul 28 comment recovering a representation from its character @JackSchmidt: Thanks. At the moment, this is more than enough for the finite case. Jul 28 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. Jul 21 comment Intertwiner in german? google books says that it is not avialable to me for viewing. Could you please give the page number? Jul 18 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.) Jul 18 comment Intertwiner in german? @AsafKaragila: Milne forgot to add explanatory notes to the 11th tip. German is not a bad languague for expressing mathematics. Jul 18 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? Jul 6 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. May 24 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.... Mar 22 comment Special solution of Helmholtz equation Thanks. This construction is good enough for me. Mar 21 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?