拉格朗日正则化方法与线性规划原—对偶算法的研究
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摘要
本论文主要对拉格朗日正则化方法和线性规划原-对偶算法进行了研究,其中,前者是一种特殊的光滑化方法,为本文线性规划原-对偶内点和非内点算法的建立提供了基础。
     极大熵方法是解有限极大极小问题的一种有效光滑化法,它通过在极大极小问题的拉格朗日函数上引进Shannon信息熵作正则项,给出一致逼近极大值函数的光滑函数。因该函数所具有的优良性质,使其在求解各类优化问题中得到了广泛的应用。
     本文从两个方面发展了这种熵正则化方法,即将其从极大极小问题推广到一般不等式约束优化问题上和用一般函数代替熵函数作正则项,建立新的正则化方法。为了克服不可微正齐次函数δ(·|R_-~m)给约束优化问题的等价无约束形式求解带来的困难,我们将其目标函数M(x)重新用一个以经典拉格朗日函数为目标的锥优化问题来表示。当将熵函数作为正则项加到拉格朗日函数上,我们得到了逐点逼近于M(x)的光滑函数。经证明,该函数即为指数罚函数。在此基础上,通过用一般可分离乘子函数代替熵函数作正则项,建立了一种新型正则化方法,即拉格朗日正则化法。该方法不仅提供了统一光滑不可微函数M(x)和δ(·|R_-~m)的办法,而且还给出了一种构造罚函数的统一框架,由此将罚函数与经典拉格朗日函数从对偶空间的角度联系在一起。
     本文上篇共含四章,主要进行拉格朗日正则化法的研究。第一章为绪论,简单描述了熵正则化方法与罚函数法的研究现状;第二章,针对有限极大极小问题,通过研究熵正则化方法与指数(乘子)罚函数方法之间的关系,揭示熵正则方法的数学本质;第三章将极大熵方法推广到一般不等式约束优化问题上,建立了拉格朗日正则化方法;第四章利用第三章建立的拉格朗日正则化方法,给出一种构造罚函数的统一框架,并通过具体的罚和障碍函数例子加以说明。
     本文下篇集中建立求解线性规划的有效原-对偶算法。在各种内点法里,最
    
    成功的也是最为有效的当属原一对偶路径跟踪算法.但现有的算法几乎都是基于
    标准摄动方程组,即标准线性规划对数障碍问题的卜K-T系统,建立起来的。
    本文从三个不同的角度来改造此摄动方程组,并建立相应的原一对偶路径跟踪内
    点和非内点算法。
     经过对标准中心化方程Xs二户。实施代数等价变换,我们得到了一个新的扰
    动K一K一T方程组,并针对具体的幕变换,由此摄动方程组给出了彭积明等人在缩
    减大步算法的复杂性界限时所使用的牛顿方程。在这一事实和彭等人的出色结果
    激发下,我们利用一个特殊的代数变换一对数变换,建立一个不可行大步原一对偶
    路径跟踪内点算法。该算法在遵循中心路径的同时,沿着原一对偶嫡函数的最速
    下降方向达到线性规划的原一对偶解集。另外,基于min一Inax本身所具有的“均
    化”作用,我们定义了一个新的邻近度量函数,并以其最优性条件作为中心化方
    程。其目的是在摄动方程本身建立一种自调节机制,以使牛顿方向能够根据上一
    次迭代点的信息在各个互补对之间作出自适应的调整。前述的两种方法是针对扰
    动K一K一T系统进行的,而本文的另一种方法是采用NCP函数,直接将标准线性规
    划K一K一T条件化为一个不含内点约束的等价方程组,以此改造标准摄动方程组。
     下篇由后四章组成。第五章简单回顾了线性规划及内点法,并重点介绍了原
    一对偶路径跟踪内点算法。第六章研究了对标准中心化方程实施代数等价变换的
    作用,并特别就对数变换情形,建立一个不可行大步原一对偶路径跟踪内点算法,
    同时给出其收敛性及复杂性界限分析。第七章,通过构造一个新的邻近度量函数,
    提出一个具有自调节功能的原一对偶路径跟踪内点算法,并将其与线性规划软件
    LIPSOL和彭等人的M。IPM进行数值比较,证实了该算法的有效性;第八章,基
    于NCP函数及其光滑函数,建立求解线性规划的非内点原一对偶路径跟踪算法,
    并给出相应的全局及局部收敛性分析。
This dissertation is devoted to studying Lagrangian regularization approach and primal-dual algorithms for linear programming, of which the former is a kind of special smoothing methods that provide a basis for developing the primal-dual interior point and non-interior point algorithms for linear programming.
    Maximum Entropy Method is an effective smoothing one for the finite min-max problem, which, by adding Shannon's informational entropy as a regularizing term to the Lagrangian function of min-max problem, yields a smooth function that uniformly approaches the non-smooth max-valued function. Due to the excellent properties of this smooth function, this method is extensively applied to many kinds of optimization problems.
    In this thesis, we extend the entropy regularization method in two ways: from the min-max problem to general inequality constrained optimization problems and from the entropy function to more general functions. To circumvent the non-differentiable
    difficulty caused by the positive homogeneously function that is involved in an equivalent unconstrained formulation
    for general inequality constrained optimization problems, we turn to the classical Lagrangian function and redefine M (x) by a conic optimization problem with the
    Lagrangian as the objective function. When adding an entropy function as regularizing term to the Lagrangian function, we obtain a smooth approximate function for M(x) , which turns out to be the exponential penalty function.
    Furthermore, when replacing the entropy function by a general separate multiplier function, we develop a new regularization approach, referred to as Lagrangian regularization approach. This approach does not only provide a unified smoothing
    technique for the non-differentiable M(x) and but also offers a unified
    
    
    
    framework for constructing penalty functions, whereby building a bridge between the penalty functions and the classical Lagrangian.
    The first part of this dissertation is composed of four chapters, concentrating on the study for Lagrangian regularization approach. The first chapter is the introduction for the entropy regularization method and penalty function method. The second chapter reveals the mathematical essence of entropy regularization method for the finite min-max problem, through exploring the relationship between entropy regularization method and exponential penalty function method. The third chapter extends Maximum Entropy Method to a general inequality constrained optimization problem and establishes the Lagrangian regularization approach. The fourth chapter presents a unified framework for constructing penalty functions by virtue of the Lagrangian regularization approach, and illustrates it by some specific penalty and barrier function examples.
    The second part of this dissertation is committed to developing the effective primal-dual path following algorithms for linear programming. Among various types of interior point methods, the so-called primal-dual path following algorithm is the most successful and effective one. However, the existing algorithms are almost based on the standard perturbed system, namely the K-K-T system of logarithmic barrier problem for standard linear programming. In this thesis, we modify the perturbed system from three different angles and develop the corresponding primal-dual path following interior point and non-interior point algorithms.
    By making algebraically equivalent transformation for the standard centering equation Xs=μe, we obtain a new system of perturbed K-K-T equations and, for
    specific power transformation, recover the Newton equations that are recently used by J. M. Peng et al to show a lower polynomial complexity bound for large-update algorithm. Motivated by this fact and Peng's promising result, we utilize a special algebraic transformation, namely logarithmic transformation, to establish a non-infeasible long-step primal-dual path following algorithm. This algorithm arrives at the primal-dual solution set along the steepest descent direction of primal-dual
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