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We describe the orbit space of the action of the group Sp(2)Sp(1) on the real Grassmann manifolds Grk(H2) in terms of certain quaternionic matrices of Moore rank not larger than 2. We then give a complete classification of valuations on the quaternionic plane H2 which are invariant under the action of the group Sp(2)Sp(1). 相似文献
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It is well-known that an Rn-valued random vector (X1,X2,?,Xn) is comonotonic if and only if (X1,X2,?,Xn) and (Q1(U),Q2(U),?,Qn(U)) coincide in distribution, for any random variable U uniformly distributed on the unit interval (0,1), where Qk(⋅) are the quantile functions of Xk, k=1,2,?,n. It is natural to ask whether (X1,X2,?,Xn) and (Q1(U),Q2(U),?,Qn(U)) can coincide almost surely for some special U. In this paper, we give a positive answer to this question by construction. We then apply this result to a general behavioral investment model with a law-invariant preference measure and develop a universal framework to link the problem to its quantile formulation. We show that any optimal investment output should be anti-comonotonic with the market pricing kernel. Unlike previous studies, our approach avoids making the assumption that the pricing kernel is atomless, and consequently, we overcome one of the major difficulties encountered when one considers behavioral economic equilibrium models in which the pricing kernel is a yet-to-be-determined unknown random variable. The method is applicable to general models such as risk sharing model. 相似文献
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Given n independent standard normal random variables, it is well known that their maxima Mn can be normalized such that their distribution converges to the Gumbel law. In a remarkable study, Hall proved that the Kolmogorov distance dn between the normalized Mn and its associated limit distribution is less than 3/log?n. In the present study, we propose a different set of norming constants that allow this upper bound to be decreased with dn≤C(m)/log?n for n≥m≥5. Furthermore, the function C(m) is computed explicitly, which satisfies C(m)≤1 and limm→∞?C(m)=1/3. As a consequence, some new and effective norming constants are provided using the asymptotic expansion of a Lambert W type function. 相似文献
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Let G be a simple connected graph of order n with degree sequence d1,d2,…,dn in non-increasing order. The signless Laplacian spectral radius ρ(Q(G)) of G is the largest eigenvalue of its signless Laplacian matrix Q(G). In this paper, we give a sharp upper bound on the signless Laplacian spectral radius ρ(Q(G)) in terms of di, which improves and generalizes some known results. 相似文献
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Let F be an infinite field with characteristic not equal to two. For a graph G=(V,E) with V={1,…,n}, let S(G;F) be the set of all symmetric n×n matrices A=[ai,j] over F with ai,j≠0, i≠j if and only if ij∈E. We show that if G is the complement of a partial k -tree and m?k+2, then for all nonsingular symmetric m×m matrices K over F, there exists an m×n matrix U such that UTKU∈S(G;F). As a corollary we obtain that, if k+2?m?n and G is the complement of a partial k-tree, then for any two nonnegative integers p and q with p+q=m, there exists a matrix in S(G;R) with p positive and q negative eigenvalues. 相似文献
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Let f:M→N be a smooth area decreasing map between two Riemannian manifolds (M,gM) and (N,gN). Under weak and natural assumptions on the curvatures of (M,gM) and (N,gN), we prove that the mean curvature flow provides a smooth homotopy of f to a constant map. 相似文献
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We study the problem of propagation of analytic regularity for semi-linear symmetric hyperbolic systems. We adopt a global perspective and we prove that if the initial datum extends to a holomorphic function in a strip of radius (= width) ε0, the same happens for the solution u(t,⋅) for a certain radius ε(t), as long as the solution exists. Our focus is on precise lower bounds on the spatial radius of analyticity ε(t) as t grows. 相似文献
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Let S(Gσ) be the skew adjacency matrix of the oriented graph Gσ of order n and λ1,λ2,…,λn be all eigenvalues of S(Gσ). The skew spectral radius ρs(Gσ) of Gσ is defined as max{|λ1|,|λ2|,…,|λn|}. In this paper, we investigate oriented graphs whose skew spectral radii do not exceed 2. 相似文献
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Direct substitution xk+1=g(xk) generally represents iterative techniques for locating a root z of a nonlinear equation f(x). At the solution, f(z)=0 and g(z)=z. Efforts continue worldwide both to improve old iterators and create new ones. This is a study of convergence acceleration by generating secondary solvers through the transformation gm(x)=(g(x)-m(x)x)/(1-m(x)) or, equivalently, through partial substitution gmps(x)=x+G(x)(g-x), G(x)=1/(1-m(x)). As a matter of fact, gm(x)≡gmps(x) is the point of intersection of a linearised g with the g=x line. Aitken's and Wegstein's accelerators are special cases of gm. Simple geometry suggests that m(x)=(g′(x)+g′(z))/2 is a good approximation for the ideal slope of the linearised g . Indeed, this renders a third-order gm. The pertinent asymptotic error constant has been determined. The theoretical background covers a critical review of several partial substitution variants of the well-known Newton's method, including third-order Halley's and Chebyshev's solvers. The new technique is illustrated using first-, second-, and third-order primaries. A flexible algorithm is added to facilitate applications to any solver. The transformed Newton's method is identical to Halley's. The use of m(x)=(g′(x)+g′(z))/2 thus obviates the requirement for the second derivative of f(x). Comparison and combination with Halley's and Chebyshev's solvers are provided. Numerical results are from the square root and cube root examples. 相似文献
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Let (R,m,K) be a regular local ring containing a field k such that either char k=0 or char k=p and tr-deg K/Fp?1. Let g1,…,gt be regular parameters of R which are linearly independent modulo m2. Let A=Rg1?gt[Y1,…,Ym,f1(l1)−1,…,fn(ln)−1], where fi(T)∈k[T] and li=ai1Y1+?+aimYm with (ai1,…,aim)∈km−(0). Then every projective A-module of rank ?t is free. Laurent polynomial case fi(li)=Yi of this result is due to Popescu. 相似文献
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Consider in a real Hilbert space H the Cauchy problem (P0): u′(t)+Au(t)+Bu(t)=f(t), 0≤t≤T; u(0)=u0, where −A is the infinitesimal generator of a C0-semigroup of contractions, B is a nonlinear monotone operator, and f is a given H-valued function. Inspired by the excellent book on singular perturbations by J.L. Lions, we associate with problem (P0) the following regularization (Pε): −εu″(t)+u′(t)+Au(t)+Bu(t)=f(t), 0≤t≤T; u(0)=u0, u′(T)=uT, where ε>0 is a small parameter. We investigate existence, uniqueness and higher regularity for problem (Pε). Then we establish asymptotic expansions of order zero, and of order one, for the solution of (Pε). Problem (Pε) turns out to be regularly perturbed of order zero, and singularly perturbed of order one, with respect to the norm of C([0,T];H). However, the boundary layer of order one is not visible through the norm of L2(0,T;H). 相似文献