带一个形状参数的有理三次三角Bézier曲线

构造了带一个形状参数的有理三次三角Bézier曲线,它不但具有传统三次有理Bézier曲线的几何性质,而且比传统有理Bézier曲线具有更灵活的形状调整能力.讨论了两段有理三次三角Bézier曲线的G~1和C~2拼接条件,并给出了这类曲线的应用.     

一类含参数均匀三角样条插值曲线

基于一类C3连续的三角样条基函数,首先分别构造了含参数α的C2和C3连续的三角样条插值曲线,然后通过在基函数中引入参数λ,构造了含两个参数α,λ的形状可调控插值曲线,通过α,λ的不同取值,可得到一类有较好保凸和保单调效果的插值曲线,最后用图例验证了理论的有效性和正确性.     

三角域上带两个形状参数的Bézier曲面的扩展

给出了三角域上带双参数λ1,λ2的类三次Bernstein基函数,它是三角域上三次Bernstein基函数的扩展.分析了该组基的性质并定义了三角域上带有两个形状参数λ1,λ2的类三次Bernstein-Bézier(B-B)参数曲面.该基函数及参数曲面分别具有与三次Bernstein基函数及三次B-B参数曲面类似的性质.当λ1,λ2取特殊的值时,可分别得到三次Bernstein基函数及三次B-B参数曲面以及参考文献中所定义的类三次Bernstein基函数及类三次B-B参数曲面.由实例可知,通过改变形状参数的取值,可以调整曲面的形状.     

二次带形状参数双曲B样条曲线

在空间Ω_5=span{1,sinh t,cosh t,sinh 2t,cosh 2t}上给出了二次带形状参数双曲B样条的基函数.由这组基组成的二次双曲B样条曲线是C~1连续的,同时具有很多与二次B样条曲线类似的性质和几何结构,并且可以精确表示双曲线.在控制多边形固定的情况下,可以通过调节形状参数的大小来进一步调整曲线的形状.     

二次样条的一种推广

在样条函数的讨论中,除了通常的多项式样条,T-样条等外,[1,2,3]分别讨论了更为一般的样条,本文考虑二次样条的一种推广,二次多项式样条是满足一定光滑性条件的分段二次多项式.设Δ:0=x_0相似文献   

与给定多边形相切的一类含参数三角样条曲线

基于一类与给定多边形相切的三角样条曲线,通过在基函数中引入形状参数λ,在保持原曲线的光滑性及其他基本性质不变的条件下,构造出一类能自由调控曲线形态的含参数三角样条曲线,并结合图例讨论了其相关性质.     

一类可调的插值向量样条——PB 样条曲线

在几何外形的计算机辅助设计中,已有的用于插值的三次样条曲线一般都是整体构造,计算上表现为需要求解一个三对角方程组,不易于局部修改.本文利用轴向任意的抛物线调配的方法,构造了一种可控制的空间插值三次参数样条——PB 样条曲线.它的特点是几何不变,构造局部,计算简单不需要迭代反解,保凸性能较好,局部修改方便,并可拓广到曲面的插值中去.文中分析了它的几何性质和保凸条件,得出了光顺性定理,并提出了调整参量 λ_i 进行局部修改消除多余拐点和控制形状的方法.根据本文的算法编制的程序 NNP 用于构造曲线取得了良好的效果.     

Bézier曲面片光滑连接的几何条件

曲面造型是计算几何领域中一个重要的研究方向,它在汽车、造船、航空、模具等行业的外形设计和制造中有着广泛的应用,目前还在发展之中.Bézier 曲面和 B 样条曲面是当前曲面造型的两大主要方法,各有长处,互相补充.B 样条曲面具有连续性高,整体配置顶点的优点.Bézier 曲面则有装配灵活、适应性强的优点.我们将矩形域和三角域两种 Bézier 曲面片混合造型,几乎可以构造出任意形状的曲面,而这对 B 样条曲面说来则     

一类四次有理插值样条的点控制

构造了一种有理四次插值样条,其分子为四次多项式分母为二次多项式.该有理插值样条是有界的、保单调且C~2连续的,仅带有一个调节参数δ_i.研究了有理四次插值样条的性质,同时给出了相应的函数值控制、导数值控制方法,这种方法的优点在于能够根据实际设计需要简单地选取适宜的参数,达到对曲线的形状进行局部调控的目的.     

C^3连续的保形插值三角样本曲线

本给出了构造保形插值曲线的三角样条方法，即在每两个型值点之间构造两段三次参数三角样条曲线。所构造的插值曲线是局部的，保形的和C^3连续的而且曲线的形状可由参数调节。     

离散型p次Dirichlet型第一特征值

设μ=(μ_i)_i≥0为Z_+上的测度且p 1,考虑下述离散型p次Dirichlet型D_p(f)=Σ_(i=0)~∞μ_ib_i(f_i-f_(i+1))(f_i~(p-1)-f_(i+1)~(p-1)),f≥0,其中(b_i)_(i≥0)为Z_+上的正序列.本文旨在给出空间L~p(μ)上p次Dirichlet型D_p(f)所对应的第一特征值λ_(0,p)=inf{D_p(f):‖f‖_p=1,f非负且具有紧支撑}的上下界精细估计.     

加权Bloch空间上复合算子的线性组合

设λi(i= 1,..,N)是一列非0的数,D是一维复平面C的开单位圆盘,φi (i = 1,...,N)是D的解析自映射,本文研究了定义在加权Bloch空间上复合算子线性组合∑Ni=1λiCψi的紧致性.     

Projective Dirichlet boundary condition with applications to a geometric problem

Given a domain Ω ? R~n, let λ 0 be an eigenvalue of the elliptic operator L :=Σ!(i,j)~n =1?/?xi(a~(ij0 ?/?xj) on Ω for Dirichlet condition. For a function f ∈ L~2(Ω), it is known that the linear resonance equation Lu + λu = f in Ω with Dirichlet boundary condition is not always solvable.We give a new boundary condition P_λ(u|? Ω) = g, called to be pro jective Dirichlet condition, such that the linear resonance equation always admits a unique solution u being orthogonal to all of the eigenfunctions corresponding to λ which satisfies ||u||2,2 ≤ C(||f ||_2 +|| g||_(2,2)) under suitable regularity assumptions on ?Ω and L, where C is a constant depends only on n, Ω, and L. More a priori estimates,such as W~(2,p)-estimates and the C~(2,α)-estimates etc., are given also. This boundary condition can be viewed as a generalization of the Dirichlet condition to resonance equations and shows its advantage when applying to nonlinear resonance equations. In particular, this enables us to find the new indicatrices with vanishing mean(Cartan) torsion in Minkowski geometry. It is known that the geometry of indicatries is the foundation of Finsler geometry.     

幂次为2,3,4,5的素变量非线性型的整数部分

考虑了一个混合幂次为2,3,4,5的素变量非线性型的整数部分表示无穷多素数的问题.运用Davenport-Heilbronn方法证明了:如果λ_1,λ_2,λ_3,λ_4是正实数,至少有一个λ_i/λ_j(1≤ij≤4)是无理数,那么存在无穷多素数p_1,p_2,p_3,p_4,p,使得[λ_1p_1~2+λ_2p_2~3+λ_3p_3~4+λ_4p_4~5]=p.     

Multiple Positive Solutions for a Nonlinear Elliptic Equation Involving Hardy–Sobolev–Maz'ya Term

In this paper, we study the existence and nonexistence of multiple positive solutions for the following problem involving Hardy–Sobolev–Maz'ya term:-Δu- λu/|y|2=|u|pt-1u/|y|t+ μf(x), x ∈Ω,where Ω is a bounded domain in RN(N ≥ 2), 0 ∈Ω, x =(y, z) ∈ Rk× RN-kand pt =N +2-2t N-2(0 ≤ t ≤2). For f(x) ∈ C1(Ω)\{0}, we show that there exists a constant μ* 0 such that the problem possessesat least two positive solutions if μ∈(0, μ*) and at least one positive solution if μ = μ*. Furthermore,there are no positive solutions if μ∈(μ*, +∞).     

Universal C*-algebras defined by completely bounded unital homomorphisms

Suppose A is a unital C*-algebra and r 1.In this paper,we define a unital C*-algebra C_(cb)*(A,r) and a completely bounded unital homomorphism α_r:A → C_(cb)*(A,r)with the property that C_(cb)*(A,r)=C*(α_r(A))and,for every unital C*-algebra B and every unital completely bounded homomorphism φ:A→ B,there is a(unique)unital *-homomorphism π:C_(cb)*(A,r)→B such thatφ=πoα_r.We prove that,if A is generated by a normal set {t_λ:λ∈Λ},then C_(cb)*(A,r)is generated by the set {α_r(t_λ):λ∈Λ}.By proving an equation of the norms of elements in a dense subset of C_(cb)*(A,r)we obtain that,if Β is a unital C*-algebra that can be embedded into A,then C_(cb)*(B,r)can be naturally embedded into C(cb)*(A,r).We give characterizations of C_(cb)*(A,r)for some special situations and we conclude that C_(cb)*(A,r)will be "nice" when dim(A)≤ 2 and "quite complicated" when dim(A)≥ 3.We give a characterization of the relation between K-groups of A and K-groups of C_(cb)*(A,r).We also define and study some analogous of C_(cb)*(A,r).     

On Graph-Lagrangians and clique numbers of 3-uniform hypergraphs

The paper explores the connection of Graph-Lagrangians and its maximum cliques for 3-uniform hypergraphs.Motzkin and Straus showed that the Graph-Lagrangian of a graph is the Graph-Lagrangian of its maximum cliques.This connection provided a new proof of Turán classical result on the Turán density of complete graphs.Since then,Graph-Lagrangian has become a useful tool in extremal problems for hypergraphs.Peng and Zhao attempted to explore the relationship between the Graph-Lagrangian of a hypergraph and the order of its maximum cliques for hypergraphs when the number of edges is in certain range.They showed that if G is a 3-uniform graph with m edges containing a clique of order t-1,then λ(G)=λ([t-1]~((3))) provided (t-13)≤m≤(t-13)+_(t-22).They also conjectured:If G is an r-uniform graph with m edges not containing a clique of order t-1,then λ(G)λ([t-1]~((r))) provided (t-1r)≤ m ≤(t-1r)+(t-2r-1).It has been shown that to verify this conjecture for 3-uniform graphs,it is sufficient to verify the conjecture for left-compressed 3-uniform graphs with m=t-13+t-22.Regarding this conjecture,we show: If G is a left-compressed 3-uniform graph on the vertex set [t] with m edges and |[t-1]~((3))\E(G)|=p,then λ(G)λ([t-1]~((3))) provided m=(t-13)+(t-22) and t≥17p/2+11.     

核范数和谱范数下广义Sylvester方程最小二乘问题的有效算法

本文从数值角度讨论Schatten q-范数下的广义Sylvester方程约束最小二乘问题min x∈s‖N∑i=1A_iXB_i—C‖_q,其中S为闭凸约束集合,Schatten q-范数定义为‖M‖_q~q=∑_(i=1)~nσ_i~q(M),其中σ_i(M)为M∈R~(n×n)的奇异值.该问题的几类特殊情形在图像处理、控制论等领域有广泛的应用.q=2即Frobenius范数下该问题已被充分研究,故本文着重讨论q=1,+∞,即核范数和谱范数下该问题的数值求解.采用的数值方法是非精确标准容易执行的部分非精确交替方向法,并结合奇异值阈值算法,Moreau-Yosida正则化算法,谱投影算法和LSQR算法等求解相应子问题.给出算法的收敛性证明,并用数值算例验证其高效可行性.     

形状可调的C~2连续三次三角Hermite插值样条

基于函数空间{1,sint,cost,sin~2t,sin~3t,cos~3t}构造了一种形状可调的三次三角Hermite插值样条.该样条不仅具有带参数的Hermite型插值样条的主要特性,而且在插值节点为等距时可自动满足C2连续,其形状还可通过所带的参数进行调节.在适当条件下,该样条对应的Ferguson曲线可精确表示工程中一些常见的曲线.