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991.
A. Schrijver 《Combinatorica》1989,9(4):375-384
LetG be an eulerian graph embedded on the Klein bottle. Then the maximum number of pairwise edge-disjoint orientation-reversing circuits inG is equal to the minimum number of edges intersecting all orientation-reversing circuits. This generalizes a theorem of Lins for the projective plane. As consequences we derive results on disjoint paths in planar graphs, including theorems of Okamura and of Okamura and Seymour. 相似文献
992.
Minimal varieties of residuated lattices 总被引:2,自引:0,他引:2
Nikolaos Galatos 《Algebra Universalis》2005,52(2-3):215-239
In this paper we investigate the atomic level in the lattice of subvarieties of residuated lattices. In particular, we give infinitely many commutative atoms and construct continuum many non-commutative, representable atoms that satisfy the idempotent law; this answers Problem 8.6 of [12]. Moreover, we show that there are only two commutative idempotent atoms and only two cancellative atoms. Finally, we study the connections with the subvariety lattice of residuated bounded-lattices. We modify the construction mentioned above to obtain a continuum of idempotent, representable minimal varieties of residuated bounded-lattices and illustrate how the existing construction provides continuum many covers of the variety generated by the three-element non-integral residuated bounded-lattice.In Celebration of the Sixtieth Birthday of Ralph N. McKenzieReceived August 1, 2003; accepted in final form April 27, 2004. 相似文献
993.
We provide a rigorous discussion of the dipole field model which significantly improves previous treatments and clarifies the general mathematical properties of the model as a prototype of four-dimensional QFT with confining infrared singularity. By exploiting the Krein-Hilbert structure associated with the local and covariant quantization of the model, we can characterize, in a simple way, the possible physical interpretation, prove that the breaking of spacetime translation is inevitable in the physical space (mechanisms of confinement), identify a nontrivial physical vacuum sector, and discuss the breaking of symmetries and the existence and role of translationally invariant field operators, etc. 相似文献
994.
Ioannis K. Argyros 《BIT Numerical Mathematics》1990,30(1):92-100
New error bounds for the modified secant method are provided. We show that our error estimates are better than the ones already existing in the literature, under similar assumptions. 相似文献
995.
Summary In this paper we consider a class of regularization methods for a discretized version of an operator equation (which includes the case that the problem is ill-posed) with approximately given right-hand side. We propose an a priori- as well as an a posteriori parameter choice method which is similar to the discrepancy principle of Ivanov-Morozov. From results on fractional powers of selfadjoint operators we obtain convergence rates, which are (in many cases) the same for both parameter choices. 相似文献
996.
V. Totik 《Aequationes Mathematicae》1990,39(2-3):261-263
Summary We give a negative answer to a conjecture of Gy. Petruska. 相似文献
997.
Summary The topic of iterative substructuring methods, and more generally domain decomposition methods, has been extensively studied over the past few years, and the topic is well advanced with respect to first and second order elliptic problems. However, relatively little work has been done on more general constrained least squares problems (or equivalent formulations) involving equilibrium equations such as those arising, for example, in realistic structural analysis applications. The potential is good for effective use of iterative algorithms on these problems, but such methods are still far from being competitive with direct methods in industrial codes. The purpose of this paper is to investigate an order reducing, preconditioned conjugate gradient method proposed by Barlow, Nichols and Plemmons for solving problems of this type. The relationships between this method and nullspace methods, such as the force method for structures and the dual variable method for fluids, are examined. Convergence properties are discussed in relation to recent optimality results for Varga's theory ofp-cyclic SOR. We suggest a mixed approach for solving equilibrium equations, consisting of both direct reduction in the substructures and the conjugate gradient iterative algorithm to complete the computations.Dedicated to R. S. Varga on the occasion of his 60th birthdayResearch completed while pursuing graduate studies sponsored by the Department of Mathematical Sciences, US Air Force Academy, CO, and funded by the Air Force Institute of Technology, WPAFB, OHResearch supported by the Air Force under grant no. AFOSR-88-0285 and by the National Science Foundation under grant no. DMS-89-02121 相似文献
998.
Let p be a prime number and let G be a finitely generated group that is residually a finite p-group. We prove that if G satisfies a positive law on all elements of the form [a,b][c,d]i, a,b,c,d∈G and i?0, then the entire derived subgroup G′ satisfies a positive law. In fact, G′ is an extension of a nilpotent group by a locally finite group of finite exponent. 相似文献
999.
Masao Ishikawa 《Journal of Combinatorial Theory, Series A》2006,113(1):113-155
The initial purpose of the present paper is to provide a combinatorial proof of the minor summation formula of Pfaffians in [Ishikawa, Wakayama, Minor summation formula of Pfaffians, Linear and Multilinear Algebra 39 (1995) 285-305] based on the lattice path method. The second aim is to study applications of the minor summation formula for obtaining several identities. Especially, a simple proof of Kawanaka's formula concerning a q-series identity involving the Schur functions [Kawanaka, A q-series identity involving Schur functions and related topics, Osaka J. Math. 36 (1999) 157-176] and of the identity in [Kawanaka, A q-Cauchy identity involving Schur functions and imprimitive complex reflection groups, Osaka J. Math. 38 (2001) 775-810] which is regarded as a determinant version of the previous one are given. 相似文献
1000.
Angela Desai 《Indagationes Mathematicae》2006,17(3):353-359
We prove that any ?d shift of finite type with positive topological entropy has a family of subsystems of finite type whose entropies are dense in the interval from zero to the entropy of the original shift. We show a similar result for ?d sofic shifts, and also show every ?d sofic shift can be covered by a ?d shift of finite type arbitrarily close in entropy. 相似文献