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1.
For semi-continuous real functions we study different computability concepts defined via computability of epigraphs and hypographs. We call a real function f lower semi-computable of type one, if its open hypograph hypo(f) is recursively enumerably open in dom(f) × ?; we call f lower semi-computable of type two, if its closed epigraph Epi(f) is recursively enumerably closed in dom(f) × ?; we call f lower semi-computable of type three, if Epi(f) is recursively closed in dom(f) × ?. We show that type one and type two semi-computability are independent and that type three semi-computability plus effectively uniform continuity implies computability, which is false for type one and type two instead of type three. We show also that the integral of a type three semi-computable real function on a computable interval is not necessarily computable.  相似文献   

2.
We consider a box-constrained continuous global minimization problem. A new definition of filled function, namely that of globally concavized filled function, is proposed. A new two-parameter class of globally concavized filled functions A(x,k,p) is constructed, which has the same global minimizers as the problem on the solution domain if p is large enough. The minimization of A(x,k,p) can escape successfully from a previously converged local minimizer by taking increasing values of k. A dynamic globally concavized filled function method is designed based on these functions and the convergence property is proved. Numerical experiments on a set of standard testing functions show that the resulting method is competitive with some well-known global minimization methods. This research was supported partially by the NSFC under Grants 60773126 and 10301009, the NKBRSF of China under Grant 2006CB805900, and the Natural Science Foundation of Fujian province under Grant 2006J0030.  相似文献   

3.
We begin with the history of the discovery of computability in the 1930’s, the roles of Gödel, Church, and Turing, and the formalisms of recursive functions and Turing automatic machines (a-machines). To whom did Gödel credit the definition of a computable function? We present Turing’s notion [1939, §4] of an oracle machine (o-machine) and Post’s development of it in [1944, §11], [1948], and finally Kleene-Post [1954] into its present form.A number of topics arose from Turing functionals including continuous functionals on Cantor space and online computations. Almost all the results in theoretical computability use relative reducibility and o-machines rather than a-machines and most computing processes in the real world are potentially online or interactive. Therefore, we argue that Turing o-machines, relative computability, and online computing are the most important concepts in the subject, more so than Turing a-machines and standard computable functions since they are special cases of the former and are presented first only for pedagogical clarity to beginning students. At the end in §10–§13 we consider three displacements in computability theory, and the historical reasons they occurred. Several brief conclusions are drawn in §14.  相似文献   

4.
The filled function method is an effective approach to find the global minimizer. Two of the recently proposed filled functions are H(X) and L2(X). Although their numerical behavior is acceptable, they are not defined everywhere. This paper proposes a class of augmented filled functions with improved analyticity. Issues covered in the presented work include: theoretical properties, convergence analysis, geometric interpretation, algorithms, and numerical experiments. The overall performance of the new approach is comparable to the recently proposed ones.  相似文献   

5.
On countable structures computability is usually introduced via numberings. For uncountable structures whose cardinality does not exceed the cardinality of the continuum the same can be done via representations. Which representations are appropriate for doing real number computations? We show that with respect to computable equivalence there is one and only one equivalence class of representations of the real numbers which make the basic operations and the infinitary normed limit operator computable. This characterizes the real numbers in terms of the theory of effective algebras or computable structures, and is reflected by observations made in real number computer arithmetic. Demanding computability of the normed limit operator turns out to be essential: the basic operations without the normed limit operator can be made computable by more than one class of representations. We also give further evidence for the well-known non-appropriateness of the representation to some base b by proving that strictly less functions are computable with respect to these representations than with respect to a standard representation of the real numbers. Furthermore we consider basic constructions of representations and the countable substructure consisting of the computable elements of a represented, possibly uncountable structure. For countable structures we compare effectivity with respect to a numbering and effectivity with respect to a representation. Special attention is paid to the countable structure of the computable real numbers.  相似文献   

6.
This paper gives a new definition of a filled function, which eliminates certain drawbacks of the traditional definitions. Moreover, this paper proposes a quasi-filled function to improve the efficiency of numerical computation and overcomes some drawbacks of filled functions. Then, a new filled function method and a quasi-filled function method are presented for solving a class of global optimization problems. The global optimization approaches proposed in this paper will find a global minimum of original problem by implementing a local search scheme to the proposed filled function or quasi-filled function. Illustrative examples are provided to demonstrate the efficiency and reliability of the proposed scheme. This research was partially supported by Chongqing Municipal Education Commission under Grant 030809, and the Research Committee of The Hong Kong Polytechnic University. An erratum to this article is available at .  相似文献   

7.
We find the length of scales of computability potentials for n-element algebras. As a consequence, we find the length of the filter generated by the clone of a discriminant function in the lattice of clones of functions on an n-element set.  相似文献   

8.
For any class of operators which transform unary total functions in the set of natural numbers into functions of the same kind, we define what it means for a real function to be uniformly computable or conditionally computable with respect to this class. These two computability notions are natural generalizations of certain notions introduced in a previous paper co-authored by Andreas Weiermann and in another previous paper by the same authors, respectively. Under certain weak assumptions about the class in question, we show that conditional computability is preserved by substitution, that all conditionally computable real functions are locally uniformly computable, and that the ones with compact domains are uniformly computable. The introduced notions have some similarity with the uniform computability and its non-uniform extension considered by Katrin Tent and Martin Ziegler, however, there are also essential differences between the conditional computability and the non-uniform computability in question.  相似文献   

9.
The filled function method is considered as an efficient method to find the global minimum of multidimensional functions. A number of filled functions were proposed recently, most of which have one or two adjustable parameters. However, there is no efficient criterion to choose the parameter appropriately. In this paper, we propose a filled function without parameter. And this function includes neither exponential terms nor logarithmic terms so it is superior to the traditional ones. Theories of the filled function are investigated. And an algorithm which does not compute gradients during minimizing the filled function is presented. Moreover, the numerical experiments demonstrate the efficiency of the proposed filled function.  相似文献   

10.
非线性整数规划问题是一类复杂的优化问题,填充函数算法是求解整数规划问题的一类有效方法.构造一个新的单参数填充函数,分析并证明了其填充性质;然后,基于该填充函数并结合离散最速下降法提出了一种新的填充函数算法;最后,采用新算法对6个测试函数进行数值实验,结果表明该算法具有良好的计算效果,是有效可行的.  相似文献   

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