Frattini子群循环的有限$p$-群中的非交换集和极大Abel子群

设G是一个群,X是G的一个子集,若对于任意x,y∈X且x≠y,都有xy≠yx,则称X是G的一个非交换集.进一步,如果对于G中的任意其它非交换子集Y,都有|X|≥|Y|,那么称X是G的一个极大非交换集.文中确定了Frattini子群循环的有限p-群中极大非交换集和极大Abel子群的势.     

强向量拟均衡问题解的存在性(英文)

设X是一个实的Hausdorff拓扑向量空间,Y是一个实的局部凸向量空间,C是Y中的闭凸锥,K（?）X是一个紧子集.F:X×X→Y是一个双向量函数,G:K→2K是一个集合值映射.我们考虑下面的强拟均衡问题:存在x∈G（x）,使得对任意的y∈G（x）,成立F（x,y）∈C.本文证明了当F是半连续时,上述问题解的存在性结论.     

强向量拟均衡问题的存在性

设X是一个实的Hausdorff拓扑向量空间,Y是一个实的局部凸向量空间,C是Y中的闭凸锥,K X是一个紧子集.FX×X→Y是一个双向量函数,GK→2K是一个集合值映射.我们考虑下面的强拟均衡问题存在x∈G(x),使得对任意的y∈G(x),成立F(x,y)∈C.本文证明了当F是半连续时,上述问题解的存在性结论.     

L4(4)的非交换图刻画

令G是一个有限非交换群.如下定义群G的非交换图▽(G):其顶点集是G\Z(G),任意两个顶点x和y相连的充要条件是[x,y]≠1.2006年, Abdollahi A.,Akbari S.和Maimani H.R.提出了如下猜想:若群G满足条件▽(G)≌▽(M),其中M是有限非交换单群,则G≌M.尽管该猜想对于具有非连通素图的有限单群以及交错群A10足成立的,但是人们仍不知道它对于除A10外的具有连通素图的有限单群是否成立.该文证明了上述猜想对于射影特殊线性单群L4(4)也是成立的.     

3-连通3-正则图中的可序子集

图G的k元点集X={x1,x2,…,xk}被称为G的k-可序子集,如果X的任意排列都按序排在G的某个圈上.称G是k-可序图,如果G的每一个k元子集都是G的k-可序子集.称G为k-可序Hamilton图,如果X的任意排列都位于G的Hamilton圈上.研究了3-连通3-正则图的可序子集的存在性问题.     

有效极点的一个存在性定理

设 Y,∧ 均是 R~m 中的非空集合,称 x∈Y 为 Y 的一个有效点,如不存在 y∈Y,y≠x使 x∈y+∧.记 Y 的有效点集为 E(Y,∧).称 x∈Y 为 Y 的一个极点,如不存在 y∈Y,z∈Y,y≠z 使 x∈(y,z).记 Y 的极点集为 Y_e。记 Y 的有效极点集为 E_Y=Y_e∩E(Y,∧).Yu,L.P.在[1]中说明,若∧是凸锥,Y 是紧多面凸集,那么如果 E(Y,∧)≠φ,则Y 必有有效极点,即 E_Y≠φ.显然这个结论是线性多目标规划单纯形法的理论基础.     

求最佳Lagrange型插值逼近的一种方法

设W是紧空间,两点x,y间的距离用ρ(x,y)表示,对于W的任一紧子集Y,用C(Y)表示Y上的实(或复)连续函数空间。对任意g∈C(Y),定义‖g‖=sup{|g(x)|:x∈Y}。 设X是W的紧子集,Z是X的有限子集。又设F是连续依赖于参数A的逼近函数,A在实(或复)n维空间的一个非空闭子集P内取值,且对一切A∈P,均有     

关于K凹向量值函数的一类极值问题

本文讨论凸集的极值点与K凹向量值函数的一类极值问题之间的关系. 定义1 对于集合C中的点x,若有x=λy+(1-λ)z,其中0<λ<1,y,z∈C,就有x=y=z,则称x为C的极值点.C的所有极值点组成的集合记为extC. 定义2 设X,Y是实拓扑局部凸空间,Ω为X的非空紧凸子集,K为Y中的具有非     

线性目标函数下的 greedy-结构

有限集合E的一个子集类■2~E,如果对任意的 Y∈■及 X■Y,总有 X∈■,我们则称(E,■)为一独立系统.1971年 J.Edmonds 指出,独立系统(E,■)对任意线性目标函数其greedy基恒为最优基的充分必要条件是■满足交换公理,即对任意的 X,Y∈■,及|Y|>|X|,则存在 y∈Y\X,使 X∪{y}∈■.这时(E,■)是一拟阵.     

有向路和有向圈的控制集数

1引言设G=(V,E)为无向图．子集D (?)V(G)是无向图G的控制集,如果对于任意的y,∈V(G)-D,都存在x∈D,使xy∈E(G)．G的控制集D是G的分裂控制集,如果G中由V(G)-D导出的子图G〈V(G)-D〉是不连通的．G的一个控制集D是G的一个强(弱)控制集,若dG(x)≥d_G(y)(d_G(x)≤d_G(y)),其中d_G(x)表示G中与点x关联的边数．对于有向图H=(V,A),子集D(?)V(H)称为H的控制集,如果对于任意的y∈     

Determining a Rotation of a Tetrahedron from a Projection

The following problem, arising from medical imaging, is addressed: Suppose that T is a known tetrahedron in ?³ with centroid at the origin. Also known is the orthogonal projection U of the vertices of the image ?T of T under an unknown rotation ? about the origin. Under what circumstances can ? be determined from T and U?     

On a mapping of a projective space into a sphere

We obtain an exact estimate for the minimum multiplicity of a continuous finite-to-one mapping of a projective space into a sphere for all dimensions. For finite-to-one mappings of a projective space into a Euclidean space, we obtain an exact estimate for this multiplicity for n = 2, 3. For n ≥ 4, we prove that this estimate does not exceed 4. Several open questions are formulated.     

Calculating a function of a matrix with a real spectrum

Let T be a square matrix with a real spectrum, and let f be an analytic function. The problem of the approximate calculation of f(T) is discussed. Applying the Schur triangular decomposition and the reordering, one can assume that T is triangular and its diagonal entries t_ii are arranged in increasing order. To avoid calculations using the differences t_ii ? t_jj with close (including equal) t_ii and t_jj, it is proposed to represent T in a block form and calculate the two main block diagonals using interpolating polynomials. The rest of the f(T) entries can be calculated using the Parlett recurrence algorithm. It is also proposed to perform some scalar operations (such as the building of interpolating polynomials) with an enlarged number of significant decimal digits.

     

Evolution to a steady state for a rarefied gas flowing from a tank into a vacuum through a plane channel

A kinetic equation (S-model) is used to solve the nonstationary problem of a monatomic rarefied gas flowing from a tank of infinite capacity into a vacuum through a long plane channel. Initially, the gas is at rest and is separated from the vacuum by a barrier. The temperature of the channel walls is kept constant. The flow is found to evolve to a steady state. The time required for reaching a steady state is examined depending on the channel length and the degree of gas rarefaction. The kinetic equation is solved numerically by applying a conservative explicit finite-difference scheme that is firstorder accurate in time and second-order accurate in space. An approximate law is proposed for the asymptotic behavior of the solution at long times when the evolution to a steady state becomes a diffusion process.     

Torsional Oscillations of a Punch on a Layer Bonded to a Half-Space Containing a Cylindrical Cavity

A previously published algorithm [9] is implemented in application to the Reissner–Sagoci problem for a layer bonded to a half-space containing a cylindrical cavity. The influence of the mechanical and geometrical parameters of the layer and the half-space on the amplitude-frequency response curves of the punch oscillations is analyzed. Practical applications of the results are proposed for ensuring the seismic isolation of buildings on the investigated foundation in the presence of dynamic torsional excitations.     

Symmetry-based solution of a model for a combination of a risky investment and a riskless investment

Benth and Karlsen [F.E. Benth, K.H. Karlsen, A note on Merton's portfolio selection problem for the Schwartz mean-reversion model, Stoch. Anal. Appl. 23 (2005) 687-704] treated a problem of the optimisation of the selection of a portfolio based upon the Schwartz mean-reversion model. The resulting Hamilton-Jacobi-Bellman equation in 1+2 dimensions is quite nonlinear. The solution obtained by Benth and Karlsen was very ingenious. We provide a solution of the problem based on the application of the Lie theory of continuous groups to the partial differential equation and its associated boundary and terminal conditions.