Hilbert空间中一些二阶线性微分—算子方程的Cauchy问题及其近似解

我们讨论Hilbert空间中的二阶线性微分—算子方程在初始条件下的Cauchy问题的近似解。设(V,(·,·)_v,K)(W,(·,·)_w,K)分别为数域K(C或K)上具有内积(·,·)_v、(·,·)_w的Hilbert空间简记为V、W,相应的范数为||·||_v、||·||_w。V’、W’分别为其对偶空     

分布参数与集中参数耦合系统的极点配置问题

设 H 是可分的 Hilbert 空间,A 是空间 H 中的线性算子,b∈H 是非零元.考察空间H 中的一阶发展方程描述的控制系统(dx)/(dt)=Ax+bu(t),x(0)=x_0,(1)这里 u(t) 是控制量,是一数值函数.考察反馈控制律u(t)=〈x(t),g〉,(2)这里 g∈H 是非零元,〈·,·〉是 H 上的内积.     

算子的ω-非负逼近

<正> 文中 H 为可析 Hilbert 空间,H 中内积为〈·,·〉,H 中向量的范数为‖·‖,(?)(H)为H 上线性有界算子全体,对任何 T∈(?)(H),‖T‖表示算子 T 的范数.记     

Hilbert空间中线性系统的一个镇定问题

<正> 本文考察复 Hilbert 空间(?)中的线性系统(?)(1)在反馈律Gu(t)=-sum from i=1 to v b_i〈(dy)/(dt),g_i〉 (2)下的镇定问题,其中〈·,·〉表(?)中内积,d·/dt 表矢值函数“·”的微商,u(t)为数值函数.假设:(A)算子 A 为正定自伴离散谱算子,谱分解式为     

Krein空间上算子的可定化性

从Hilbert空间(H,(·,·))上的一个有界自伴算子G可以导出不定内积[·,·]:=(G·,·),本文给出了由G所导出的Krein空间上的G-自伴、G-酉以及G-正常算子的可定化、强可定化和一致可定化性质以及这三种不同的可定化性之间的关系.     

算子非负逼近端点的几个问题

<正> H表示Hilbert空间,本文中的算子都是H上的有界线性算子,<·,·>表示H中元的内积,设P是有界线性算子,如果≥0,x∈H,则称P是非负算子.H上的非负算子集合记作S,设A是有界线性算子,如果存在P_o∈S,使     

Runge-Kutta方法的(■,p,q)代数稳定性

1.引言 设X是(实或复)Hilbert空间,〈·,·〉是其中的内积,||·||是从该内积导出的范数,D是X的某一无限子集,f:[0,+∞)×D→X是一给定映射。考虑初值问题:     

Generalized Semigroup on(V, H, a)

Let V and H be two Hilbert spaces satisfying the imbedding relation V\subset H. Let $[ - \mathscr{A}:V \to V''\]$ be the linear operator determined by a(u, v) = <\mathscr{A}u, v> for u, v\in V, where a(u, v) is a continuous sesquilinear form on V satisfying $a(u, u)+\lambda|u|_H^2\geq c||u||_V^2$ for u\in V and some \lambda \in R and c>0. In this paper it is proved that —\mathscr{A} is the generator of an analytic C_0-semigroup on V''. Furthermore, if b(u, v) is a continuous sesquilinear form on HxV and \mathscr{B}: H\rightarrow V, the linear operator determined by b(u, v) = (\mathscr{B}u, v) for u, v\in V, then —\mathscr{A}—mathscr{B} is also the generator of C_0-semigroup on V''. Also, similar results are proved on “inserted” spaces V_\theta(\theta \geq -1) which are determined by the spectrum system of \mathscr{A}.     

数值积分下四阶方程协调有限元解的L_∞估计

|u|_(m,Ω), ‖u‖_(m,Ω)(以下下标为Ω时略去),p=∞时采用通常的修正定义.H(?)(Ω)是C_0~∞(Ω)在模‖·‖(?)下的闭包,(·,·)表示L_2内积。另外,记‖u‖m, ,h=(sum from e ((‖u‖_m~p),p,e)p。 讨论下列四阶方程的有限元逼近问题:     

内积函数的表示

本文首先定义了内积函数,这个概念推广了内积的定义.然后定义了Hilbert空间（H,〈·,·〉）上由严格正算子A诱导的范数,这个范数与由〈·,·〉诱导的范数是等价的.进一步,证明了所有的内积函数与线性有界的严格正算子全体之间存在一一对应关系.     

The fundamental solution of the Keldysh type operator

In this paper we discuss the fundamental solution of the Keldysh type operator $ L_\alpha u \triangleq \frac{{\partial ^2 u}} {{\partial x^2 }} + y\frac{{\partial ^2 u}} {{\partial y^2 }} + \alpha \frac{{\partial u}} {{\partial y}} $ L_\alpha u \triangleq \frac{{\partial ^2 u}} {{\partial x^2 }} + y\frac{{\partial ^2 u}} {{\partial y^2 }} + \alpha \frac{{\partial u}} {{\partial y}} , which is a basic mixed type operator different from the Tricomi operator. The fundamental solution of the Keldysh type operator with $ \alpha > - \frac{1} {2} $ \alpha > - \frac{1} {2} is obtained. It is shown that the fundamental solution for such an operator generally has stronger singularity than that for the Tricomi operator. Particularly, the fundamental solution of the Keldysh type operator with $ \alpha < \frac{1} {2} $ \alpha < \frac{1} {2} has to be defined by using the finite part of divergent integrals in the theory of distributions.     

On solutions of almost hypoelliptic equations in weighted Sobolev spaces

It is proved that if P(D) is a regular, almost hypoelliptic operator and

On n-K Width of Certain Function Classes Defined by Linear Op erators in L2 Space

Let M(u) be an N-function, Lr(f, x) and Kr(f, x) are Bak operator and Kan-torovich operator, WM(Lr(f)) and WM(Kr(f)) are the Sobolev-Orlicz classes defined by Lr(f, x), Kr(f, x) and M(u). In this paper we give the asymptotic estimates of the n?K widths dn(WM(Lr(f)),L2[0,1]) and dn(WM(Kr(f)),L2[0,1]).     

两类四阶微分算子积的自伴性研究

利用算子理论及矩阵运算方法,讨论了由两类不同的对称微分算式D~((4))+D~((2))+q_1(t)和D~((4))+q_2(t)(D=d/dt,t∈I=[a,b])生成的微分算子的积算子的自伴性,获得了积算子是自伴算子的充分必要条件.     

INITIAL VALUE PROBLEMS FOR NONLINEAR DEGENERATE SYSTEMS OF FILTRATION TYPE

In this paper, the periodic boundary problem and the initial value problem for the nonlinear system of parabolic type $\[{u_t} = (grad\varphi (u))\]$ are studied, where $\[u = ({u_1}, \cdots ,{u_N})\]$ is an N-dimensional vector valued function, $\[\varphi (u)\]$ is a strict convex function of vector variable $\[u\]$, and its matrix of derivatives of second order is zero-definite at $\[u = 0\]$. This system is degenerate. The definition of the generalized solution of the problem: $\[u(x,t) \in {L_\infty }((0,T);{L_2}(R)),\]$, grad $\[\varphi (u) \in {L_\infty }((0,T);W_2^{(1)}(R)),\]$ and it satisfies appropriate integral relation. The existence and uniqueness of the generalized solution of the problem are proved. When N=1, the system is the commonly so-called degenerate partial differential equation of filtration type.     

Inequalities and Separation for a Biharmonic Laplace-Beltrami Differential Operator in a Hilbert Space Associated with the Existence and Uniqueness Theorem

In this paper, we have studied the separation for the biharmonic Laplace-Beltrami differential operator\begin{equation*}Au(x)=-\Delta \Delta u(x)+V(x)u(x),\end{equation*}for all $x\in R^{n}$, in the Hilbert space $H=L_{2}(R^{n},H_{1})$ with the operator potential $V(x)\in C^{1}(R^{n},L(H_{1}))$, where $L(H_{1})$ is the space of all bounded linear operators on the Hilbert space $H_{1}$, while $\Delta \Delta u$\ is the biharmonic differential operator and\begin{equation*}\Delta u{=-}\sum_{i,j=1}^{n}\frac{1}{\sqrt{\det g}}\frac{\partial }{{\partial x_{i}}}\left[ \sqrt{\det g}g^{-1}(x)\frac{\partial u}{{\partial x}_{j}}\right]\end{equation*}is the Laplace-Beltrami differential operator in $R^{n}$. Here $g(x)=(g_{ij}(x))$ is the Riemannian matrix, while $g^{-1}(x)$ is the inverse of the matrix $g(x)$. Moreover, we have studied the existence and uniqueness Theorem for the solution of the non-homogeneous biharmonic Laplace-Beltrami differential equation $Au=-\Delta \Delta u+V(x)u(x)=f(x)$ in the Hilbert space $H$ where $f(x)\in H$ as an application of the separation approach.     

Dynamical system with boundary control associated with a symmetric semibounded operator

Let L ₀ be a closed densely defined symmetric semibounded operator with nonzero defect indices in a separable Hilbert space $\mathcal H$ . It determines a Green system $\{{\mathcal H}, {\mathcal B}; L_0, \Gamma_1, \Gamma_2\}$ , where ${\mathcal B}$ is a Hilbert space, and the $\Gamma_i: {\mathcal H} \to \mathcal B$ are operators connected by the Green formula $$ (L_0^*u, v)_{\mathcal H}-(u,L_0^*v)_{\mathcal H} =(\Gamma_1 u, \Gamma_2 v)_{\mathcal B} - (\Gamma_2 u, \Gamma_1 v)_{\mathcal B}. $$ The boundary space $\mathcal B$ and the boundary operators Γ _i are chosen canonically in the framework of the Vishik theory. With the Green system one associates a dynamical system with boundary control (DSBC): $$ \begin{array}{lll} && u_{tt}+L_0^*u = 0, \quad u(t) \in {\mathcal H}, \quad t>0,\\ && u\big|_{t=0}=u_t\big|_{t=0}=0, \\ && \Gamma_1 u = f, \quad f(t) \in {\mathcal B},\quad t \geq 0. \end{array} $$ We show that this system is controllable if and only if the operator L ₀ is completely non-self-adjoint. A version of the notion of wave spectrum of L ₀ is introduced. It is a topological space determined by L ₀ and constructed from reachable sets of the DSBC. Bibliography: 15 titles.     

极限点型 Sturm-Liouville 算子乘积的自伴性

假设微分算式l(y)=-(py') qy,t∈[a,∞),满足lk(y)(k=1,2,3)均为极限点型,作者研究了由l(y)生成的两个微分算子Li(i=1,2)的乘积L2L1的自伴性问题并获得其自伴的充分必要条件．同时研究了由l(y)=-y" qy,t∈[a,∞),生成的三个微分算子Li(i=1,2,3)的乘积L3L2L1的自伴性问题．     

Boundary values of generalized solutions of a homogeneous sturm — Liouville equation in a space of vector functions

We consider a differential equation of the form ?y” + A²y=0, where A is a self-adjoint operator in a Hilbert space H. We show that each generalized solution of this equation inw _?m (0, b) (0 < b < ∞, m ≥ 0) has boundary values in the spaceH _?m?1/2, where H_J (?∞ ?m(0, b) is the space of continuous linear functionals on ?W_m(0, b), the completion of the space of infinitely differentiable vector functions with compact support with respect to the norm \(\left\| u \right\|_{W_m (0, b) = (\left\| u \right\|_{L_2 (H_{m,} (0, b))} + \left\| u \right\|_{L_2 (H, (0, b))}^{(m)} )} \) . It follows that each function u(t, x) which is harmonic in the strip G = [0, b] x (?∞, ∞) and which is in the space that is dual to ? ₂ ^m (G) has limiting values as t→0 and t→b in the space \(W_2^{ - m - {\raise0.7ex\hbox{\(1\)} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-0em}\!\lower0.7ex\hbox{\(2\)}}} ( - \infty ,\infty )\) .     

Discontinuous Sturm-Liouville problems involving an abstract linear operator

In this paper we introduce to consideration a new type boundary value problems consisting of an ``Sturm-Liouville" equation on two disjoint intervals as $$-p(x)y^{\prime \prime }+ q(x)y+\mathfrak{B}y|_{x} = \mu y , x\in [a,c)\cup(c,b]$$ together with two end-point conditions whose coefficients depend linearly on the eigenvalue parameter, and two supplementary so-called transmission conditions, involving linearly left-hand and right-hand values of the solution and its derivatives at point of interaction $x=c,$ where $\mathfrak{B}:L_{2}(a,c)\oplus L_{2}(c,b)\rightarrow L_{2}(a,c)\oplus L_{2}(c,b)$ is an abstract linear operator, non-selfadjoint in general. For self-adjoint realization of the pure differential part of the main problem we define ``alternative" inner products in Sobolev spaces, ``incorporating" with the boundary-transmission conditions. Then by suggesting an own approaches we establish such properties as topological isomorphism and coercive solvability of the corresponding nonhomogeneous problem and prove compactness of the resolvent operator in these Sobolev spaces. Finally, we prove that the spectrum of the considered eigenvalue problem is discrete and derive asymptotic formulas for the eigenvalues. Note that the obtained results are new even in the case when the equation is not involved an abstract linear operator $\mathfrak{B}.$