Abstract Recursion and Intrinsic Complexity
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Unfold/Fold Transformations and Loop Optimization of Logic Programs
Unfold/Fold Transformations and Loop Optimization of Logic Programs Saumya K. Debray Department of Computer Science The University of Arizona Tucson, AZ 85721 Abstract: Programs typically spend much of their execution time in loops. This makes the generation of ef®cient code for loops essential for good performance. Loop optimization of logic programming languages is complicated by the fact that such languages lack the iterative constructs of traditional languages, and instead use recursion to express loops. In this paper, we examine the application of unfold/fold transformations to three kinds of loop optimization for logic programming languages: recur- sion removal, loop fusion and code motion out of loops. We describe simple unfold/fold transformation sequences for these optimizations that can be automated relatively easily. In the process, we show that the properties of uni®cation and logical variables can sometimes be used to generalize, from traditional languages, the conditions under which these optimizations may be carried out. Our experience suggests that such source-level transformations may be used as an effective tool for the optimization of logic pro- grams. 1. Introduction The focus of this paper is on the static optimization of logic programs. Speci®cally, we investigate loop optimization of logic programs. Since programs typically spend most of their time in loops, the generation of ef®cient code for loops is essential for good performance. In the context of logic programming languages, the situation is complicated by the fact that iterative constructs, such as for or while, are unavailable. Loops are usually expressed using recursive procedures, and loop optimizations have be considered within the general framework of inter- procedural optimization. -
6.5 the Recursion Theorem
6.5. THE RECURSION THEOREM 417 6.5 The Recursion Theorem The recursion Theorem, due to Kleene, is a fundamental result in recursion theory. Theorem 6.5.1 (Recursion Theorem, Version 1 )Letϕ0,ϕ1,... be any ac- ceptable indexing of the partial recursive functions. For every total recursive function f, there is some n such that ϕn = ϕf(n). The recursion Theorem can be strengthened as follows. Theorem 6.5.2 (Recursion Theorem, Version 2 )Letϕ0,ϕ1,... be any ac- ceptable indexing of the partial recursive functions. There is a total recursive function h such that for all x ∈ N,ifϕx is total, then ϕϕx(h(x)) = ϕh(x). 418 CHAPTER 6. ELEMENTARY RECURSIVE FUNCTION THEORY A third version of the recursion Theorem is given below. Theorem 6.5.3 (Recursion Theorem, Version 3 ) For all n ≥ 1, there is a total recursive function h of n +1 arguments, such that for all x ∈ N,ifϕx is a total recursive function of n +1arguments, then ϕϕx(h(x,x1,...,xn),x1,...,xn) = ϕh(x,x1,...,xn), for all x1,...,xn ∈ N. As a first application of the recursion theorem, we can show that there is an index n such that ϕn is the constant function with output n. Loosely speaking, ϕn prints its own name. Let f be the recursive function such that f(x, y)=x for all x, y ∈ N. 6.5. THE RECURSION THEOREM 419 By the s-m-n Theorem, there is a recursive function g such that ϕg(x)(y)=f(x, y)=x for all x, y ∈ N. -
April 22 7.1 Recursion Theorem
CSE 431 Theory of Computation Spring 2014 Lecture 7: April 22 Lecturer: James R. Lee Scribe: Eric Lei Disclaimer: These notes have not been subjected to the usual scrutiny reserved for formal publications. They may be distributed outside this class only with the permission of the Instructor. An interesting question about Turing machines is whether they can reproduce themselves. A Turing machine cannot be be defined in terms of itself, but can it still somehow print its own source code? The answer to this question is yes, as we will see in the recursion theorem. Afterward we will see some applications of this result. 7.1 Recursion Theorem Our end goal is to have a Turing machine that prints its own source code and operates on it. Last lecture we proved the existence of a Turing machine called SELF that ignores its input and prints its source code. We construct a similar proof for the recursion theorem. We will also need the following lemma proved last lecture. ∗ ∗ Lemma 7.1 There exists a computable function q :Σ ! Σ such that q(w) = hPwi, where Pw is a Turing machine that prints w and hats. Theorem 7.2 (Recursion theorem) Let T be a Turing machine that computes a function t :Σ∗ × Σ∗ ! Σ∗. There exists a Turing machine R that computes a function r :Σ∗ ! Σ∗, where for every w, r(w) = t(hRi; w): The theorem says that for an arbitrary computable function t, there is a Turing machine R that computes t on hRi and some input. Proof: We construct a Turing Machine R in three parts, A, B, and T , where T is given by the statement of the theorem. -
A Right-To-Left Type System for Value Recursion
1 A right-to-left type system for value recursion 61 2 62 3 63 4 Alban Reynaud Gabriel Scherer Jeremy Yallop 64 5 ENS Lyon, France INRIA, France University of Cambridge, UK 65 6 66 1 Introduction Seeking to address these problems, we designed and imple- 7 67 mented a new check for recursive definition safety based ona 8 In OCaml recursive functions are defined using the let rec opera- 68 novel static analysis, formulated as a simple type system (which we 9 tor, as in the following definition of factorial: 69 have proved sound with respect to an existing operational seman- 10 let rec fac x = if x = 0 then 1 70 tics [Nordlander et al. 2008]), and implemented as part of OCaml’s 11 else x * (fac (x - 1)) 71 type-checking phase. Our check was merged into the OCaml distri- 12 Beside functions, let rec can define recursive values, such as 72 bution in August 2018. 13 an infinite list ones where every element is 1: 73 Moving the check from the middle end to the type checker re- 14 74 let rec ones = 1 :: ones stores the desirable property that compilation of well-typed programs 15 75 Note that this “infinite” list is actually cyclic, and consists of asingle does not go wrong. This property is convenient for tools that reuse 16 76 cons-cell referencing itself. OCaml’s type-checker without performing compilation, such as 17 77 However, not all recursive definitions can be computed. The MetaOCaml [Kiselyov 2014] (which type-checks quoted code) and 18 78 following definition is justly rejected by the compiler: Merlin [Bour et al. -
The Logic of Recursive Equations Author(S): A
The Logic of Recursive Equations Author(s): A. J. C. Hurkens, Monica McArthur, Yiannis N. Moschovakis, Lawrence S. Moss, Glen T. Whitney Source: The Journal of Symbolic Logic, Vol. 63, No. 2 (Jun., 1998), pp. 451-478 Published by: Association for Symbolic Logic Stable URL: http://www.jstor.org/stable/2586843 . Accessed: 19/09/2011 22:53 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Association for Symbolic Logic is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Symbolic Logic. http://www.jstor.org THE JOURNAL OF SYMBOLIC LOGIC Volume 63, Number 2, June 1998 THE LOGIC OF RECURSIVE EQUATIONS A. J. C. HURKENS, MONICA McARTHUR, YIANNIS N. MOSCHOVAKIS, LAWRENCE S. MOSS, AND GLEN T. WHITNEY Abstract. We study logical systems for reasoning about equations involving recursive definitions. In particular, we are interested in "propositional" fragments of the functional language of recursion FLR [18, 17], i.e., without the value passing or abstraction allowed in FLR. The 'pure," propositional fragment FLRo turns out to coincide with the iteration theories of [1]. Our main focus here concerns the sharp contrast between the simple class of valid identities and the very complex consequence relation over several natural classes of models. -
Fractal Curves and Complexity
Perception & Psychophysics 1987, 42 (4), 365-370 Fractal curves and complexity JAMES E. CUTI'ING and JEFFREY J. GARVIN Cornell University, Ithaca, New York Fractal curves were generated on square initiators and rated in terms of complexity by eight viewers. The stimuli differed in fractional dimension, recursion, and number of segments in their generators. Across six stimulus sets, recursion accounted for most of the variance in complexity judgments, but among stimuli with the most recursive depth, fractal dimension was a respect able predictor. Six variables from previous psychophysical literature known to effect complexity judgments were compared with these fractal variables: symmetry, moments of spatial distribu tion, angular variance, number of sides, P2/A, and Leeuwenberg codes. The latter three provided reliable predictive value and were highly correlated with recursive depth, fractal dimension, and number of segments in the generator, respectively. Thus, the measures from the previous litera ture and those of fractal parameters provide equal predictive value in judgments of these stimuli. Fractals are mathematicalobjectsthat have recently cap determine the fractional dimension by dividing the loga tured the imaginations of artists, computer graphics en rithm of the number of unit lengths in the generator by gineers, and psychologists. Synthesized and popularized the logarithm of the number of unit lengths across the ini by Mandelbrot (1977, 1983), with ever-widening appeal tiator. Since there are five segments in this generator and (e.g., Peitgen & Richter, 1986), fractals have many curi three unit lengths across the initiator, the fractionaldimen ous and fascinating properties. Consider four. sion is log(5)/log(3), or about 1.47. -
I Want to Start My Story in Germany, in 1877, with a Mathematician Named Georg Cantor
LISTENING - Ron Eglash is talking about his project http://www.ted.com/talks/ 1) Do you understand these words? iteration mission scale altar mound recursion crinkle 2) Listen and answer the questions. 1. What did Georg Cantor discover? What were the consequences for him? 2. What did von Koch do? 3. What did Benoit Mandelbrot realize? 4. Why should we look at our hand? 5. What did Ron get a scholarship for? 6. In what situation did Ron use the phrase “I am a mathematician and I would like to stand on your roof.” ? 7. What is special about the royal palace? 8. What do the rings in a village in southern Zambia represent? 3)Listen for the second time and decide whether the statements are true or false. 1. Cantor realized that he had a set whose number of elements was equal to infinity. 2. When he was released from a hospital, he lost his faith in God. 3. We can use whatever seed shape we like to start with. 4. Mathematicians of the 19th century did not understand the concept of iteration and infinity. 5. Ron mentions lungs, kidney, ferns, and acacia trees to demonstrate fractals in nature. 6. The chief was very surprised when Ron wanted to see his village. 7. Termites do not create conscious fractals when building their mounds. 8. The tiny village inside the larger village is for very old people. I want to start my story in Germany, in 1877, with a mathematician named Georg Cantor. And Cantor decided he was going to take a line and erase the middle third of the line, and take those two resulting lines and bring them back into the same process, a recursive process. -
Lab 8: Recursion and Fractals
Lab 8: Recursion and Fractals In this lab you’ll get practice creating fractals with recursion. You will create a class that has will draw (at least) two types of fractals. Once completed, submit your .java file via Moodle. To make grading easier, please set up your class so that both fractals are drawn automatically when the constructor is executed. Create a Sierpinski triangle Step 1: In your class’s constructor, ask the user how large a canvas s/he wants. Step 2: Write a method drawTriangle that draws a triangle on the screen. This method will take the x,y coordinates of three points as well as the color of the triangle. For now, start with Step 3: In a method createSierpinski, determine the largest triangle that can fit on the canvas (given the canvas’s dimensions supplied by the user). Step 4: Create a method findMiddlePoints. This is the recursive method. It will take three sets of x,y coordinates for the outer triangle. (The first time the method is called, it will be called with the coordinates determined by the createSierpinski method.) The base case of the method will be determined by the minimum size triangle that can be displayed. The recursive case will be to calculate the three midpoints, defined by the three inputs. Then, by using the six coordinates (3 passed in and 3 calculated), the method will recur on the three interior triangles. Once these recursive calls have finished, use drawTriangle to draw the triangle defined by the three original inputs to the method. -
Functional Programming (ML)
Functional Programming CSE 215, Foundations of Computer Science Stony Brook University http://www.cs.stonybrook.edu/~cse215 Functional Programming Function evaluation is the basic concept for a programming paradigm that has been implemented in functional programming languages. The language ML (“Meta Language”) was originally introduced in the 1970’s as part of a theorem proving system, and was intended for describing and implementing proof strategies. Standard ML of New Jersey (SML) is an implementation of ML. The basic mode of computation in SML is the use of the definition and application of functions. 2 (c) Paul Fodor (CS Stony Brook) Install Standard ML Download from: http://www.smlnj.org Start Standard ML: Type ''sml'' from the shell (run command line in Windows) Exit Standard ML: Ctrl-Z under Windows Ctrl-D under Unix/Mac 3 (c) Paul Fodor (CS Stony Brook) Standard ML The basic cycle of SML activity has three parts: read input from the user, evaluate it, print the computed value (or an error message). 4 (c) Paul Fodor (CS Stony Brook) First SML example SML prompt: - Simple example: - 3; val it = 3 : int The first line contains the SML prompt, followed by an expression typed in by the user and ended by a semicolon. The second line is SML’s response, indicating the value of the input expression and its type. 5 (c) Paul Fodor (CS Stony Brook) Interacting with SML SML has a number of built-in operators and data types. it provides the standard arithmetic operators - 3+2; val it = 5 : int The Boolean values true and false are available, as are logical operators such as not (negation), andalso (conjunction), and orelse (disjunction). -
Generating Mutually Recursive Definitions
Generating Mutually Recursive Definitions Jeremy Yallop Oleg Kiselyov University of Cambridge, UK Tohoku University, Japan [email protected] [email protected] Abstract let rec s = function A :: r ! s r j B :: r ! t r j [] ! true and t = function A :: r ! s r j B :: r ! u r j [] ! false Many functional programs — state machines (Krishnamurthi and u = function A :: r ! t r j B :: r ! u r j [] ! false 2006), top-down and bottom-up parsers (Hutton and Meijer 1996; Hinze and Paterson 2003), evaluators (Abelson et al. 1984), GUI where each function s, t, and u realizes a recognizer, taking a list of initialization graphs (Syme 2006), &c. — are conveniently ex- A and B symbols and returning a boolean. However, the program pressed as groups of mutually recursive bindings. One therefore that builds such a group from a description of an arbitrary state expects program generators, such as those written in MetaOCaml, machine cannot be expressed in MetaOCaml. to be able to build programs with mutual recursion. The limited support for generating mutual recursion is a con- Unfortunately, currently MetaOCaml can only build recursive sequence of expression-based quotation: brackets enclose expres- groups whose size is hard-coded in the generating program. The sions, and splices insert expressions into expressions — but a group general case requires something other than quotation, and seem- of bindings is not an expression. There is a second difficulty: gen- ingly weakens static guarantees on the resulting code. We describe erating recursive definitions with ‘backward’ and ‘forward’ refer- the challenges and propose a new language construct for assuredly ences seemingly requires unrestricted, Lisp-like gensym, which de- generating binding groups of arbitrary size – illustrating with a col- feats MetaOCaml’s static guarantees. -
Τα Cellular Automata Στο Σχεδιασμό
τα cellular automata στο σχεδιασμό μια προσέγγιση στις αναδρομικές σχεδιαστικές διαδικασίες Ηρώ Δημητρίου επιβλέπων Σωκράτης Γιαννούδης 2 Πολυτεχνείο Κρήτης Τμήμα Αρχιτεκτόνων Μηχανικών ερευνητική εργασία Ηρώ Δημητρίου επιβλέπων καθηγητής Σωκράτης Γιαννούδης Τα Cellular Automata στο σχεδιασμό μια προσέγγιση στις αναδρομικές σχεδιαστικές διαδικασίες Χανιά, Μάιος 2013 Chaos and Order - Carlo Allarde περιεχόμενα 0001. εισαγωγή 7 0010. χάος και πολυπλοκότητα 13 a. μια ιστορική αναδρομή στο χάος: Henri Poincare - Edward Lorenz 17 b. το χάος 22 c. η πολυπλοκότητα 23 d. αυτοοργάνωση και emergence 29 0011. cellular automata 31 0100. τα cellular automata στο σχεδιασμό 39 a. τα CA στην στην αρχιτεκτονική: Paul Coates 45 b. η φιλοσοφική προσέγγιση της διεπιστημονικότητας του σχεδιασμού 57 c. προσομοίωση της αστικής ανάπτυξης μέσω CA 61 d. η περίπτωση της Changsha 63 0101. συμπεράσματα 71 βιβλιογραφία 77 1. Metamorphosis II - M.C.Escher 6 0001. εισαγωγή Η επιστήμη εξακολουθεί να είναι η εξ αποκαλύψεως προφητική περιγραφή του κόσμου, όπως αυτός φαίνεται από ένα θεϊκό ή δαιμονικό σημείο αναφοράς. Ilya Prigogine 7 0001. 8 0001. Στοιχεία της τρέχουσας αρχιτεκτονικής θεωρίας και μεθοδολογίας προτείνουν μια εναλλακτική λύση στις πάγιες αρχιτεκτονικές μεθοδολογίες και σε ορισμένες περιπτώσεις υιοθετούν πτυχές του νέου τρόπου της κατανόησής μας για την επιστήμη. Αυτά τα στοιχεία εμπίπτουν σε τρεις κατηγορίες. Πρώτον, μεθοδολογίες που προτείνουν μια εναλλακτική λύση για τη γραμμικότητα και την αιτιοκρατία της παραδοσιακής αρχιτεκτονικής σχεδιαστικής διαδικασίας και θίγουν τον κεντρικό έλεγχο του αρχιτέκτονα, δεύτερον, η πρόταση μιας μεθοδολογίας με βάση την προσομοίωση της αυτο-οργάνωσης στην ανάπτυξη και εξέλιξη των φυσικών συστημάτων και τρίτον, σε ορισμένες περιπτώσεις, συναρτήσει των δύο προηγούμενων, είναι μεθοδολογίες οι οποίες πειραματίζονται με την αναδυόμενη μορφή σε εικονικά περιβάλλοντα. -
Recursion Theory Notes, Fall 2011 0.1 Introduction
Recursion Theory Notes, Fall 2011 Lecturer: Lou van den Dries 0.1 Introduction Recursion theory (or: theory of computability) is a branch of mathematical logic studying the notion of computability from a rather theoretical point of view. This includes giving a lot of attention to what is not computable, or what is computable relative to any given, not necessarily computable, function. The subject is interesting on philosophical-scientific grounds because of the Church- Turing Thesis and its role in computer science, and because of the intriguing concept of Kolmogorov complexity. This course tries to keep touch with how recursion theory actually impacts mathematics and computer science. This impact is small, but it does exist. Accordingly, the first chapter of the course covers the basics: primitive recur- sion, partial recursive functions and the Church-Turing Thesis, arithmetization and the theorems of Kleene, the halting problem and Rice's theorem, recur- sively enumerable sets, selections and reductions, recursive inseparability, and index systems. (Turing machines are briefly discussed, but the arithmetization is based on a numerical coding of combinators.) The second chapter is devoted to the remarkable negative solution (but with positive aspects) of Hilbert's 10th Problem. This uses only the most basic notions of recursion theory, plus some elementary number theory that is worth knowing in any case; the coding aspects of natural numbers are combined here ingeniously with the arithmetic of the semiring of natural numbers. The last chapter is on Kolmogorov complexity, where concepts of recursion theory are used to define and study notions of randomness and information content.