lecture25

# lecture25 - Lecture 25 Recursive Definitions Announcement...

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Lecture 25 Recursive Definitions

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Announcement Quiz on Friday Chapters: three (excluding 3.7 and 3.8) and four (including 4.1, 4.2, 4.3) But of course you should know basic definitions from earlier chapters (e.g. sets, functions, etc.)
Recursive Functions We can define a function recursively by specifying: Basis: the value of the function at the smallest element of the domain. E.g.: f(0) = 1 Recursive step: A rule for finding the value of the function at an integer from its values at smaller integers E.g: f(n+1) = 2*f(n) Many common functions can be defined recursively.

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Examples F(n) = n! recursively: F(0) = 1 F(n) = n*F(n-1) F(n) = 1 + 2 + … + n F(1) = 1 F(n+1) = (n+1) + F(n)
Fibonacci Numbers F(0) = 0 F(1) = 1 F(n) = F(n-1) + F(n-2) 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Fibonacci Numbers

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Let = (1+ 5)/2 = 1.61803… For n 3, F(n) > n-2 Proof by induction. Hint for the inductive step:
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## This note was uploaded on 10/21/2011 for the course CSCI 2011 taught by Professor Staff during the Spring '08 term at Minnesota.

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lecture25 - Lecture 25 Recursive Definitions Announcement...

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