tailieunhanh - Bài giảng Lý thuyết tính toán: Chương 5 - PGS.TS. Phan Huy Khánh

Chương 5 của bài giảng Lý thuyết tính toán giới thiệu về hàm đệ quy. Chương này trình bày một số nội dung cơ bản như sau: Gödel's incompleteness theorem; zero, successor, projector functions; functional composition; primitive recursion; proving functions are primitive recursive, Ackermann's function. . | 3 Chương 5 Hàm đệ quy Lý thuyết tính toán Theory of Computation . Phan Huy Khánh khanhph@ Chương 5 Hàm đệ quy K Recursive Function Theory Godel s Incompleteness Theorem Zero Successor Projector Functions Functional Composition Primitive Recursion Proving Functions are Primitive Re -ri Ackermann s Function 2 32 3 Computation K Get N a set of Natural Numbers N 0 1 2 . K Building the functions on N For examples x y x y xy x2 y2 are computable functions 4 32 Complicated Functions Function is computable x y z K is complicated functions from the addition and multiplication function K is computable there is a sequence of operations of the addition and the multiplication Attention There are also many functions that are not composed from the basis functions Factorial function n n n-1 n-2 . 2 1 is computable there is a sequence of multiplication operations K The factorial function is not alone the composition of the addition and multiplication operations K The number of multiplication oprations depends on n 5 32 6 32 1 Recursivity Function is computable Factorial function is a recursive definition Why is computable 0 1 n 1 n 1 n Uses the recursivity to define some functions f n 1 is defined from f n Start at f 0 Basic primitive recursive functions Computation on the natural number N Primitive Recursive Function Any function built from the basic primitive recursive functions 7 32 8 32 Computable functions Godel s Incompleteness Theorem Basic set of Recursive primitive functions Primitive Recursive Functions Mechanism for composition of functions by combining previously-defined functions composition and or recursive definitions Clearly they are infinite in number Any interesting consistent system must be incomplete that is it must contain some unprovable propositions Hierarchy of Functions 1. Primitive-Recursive Functions 2. Recursive -recursive Functions 3. Interesting well-defined Functions but unprovable BB Function Some can have any arity unary binary . f ni n2

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