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Engineering LibreTexts

19.7: One More Example

  • Page ID
    16965
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

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    After factorial, the most common example of a recursively defined mathematical function is fibonacci, which has the following definition (see http://en.Wikipedia.org/wiki/Fibonacci_number):

    \[ fibonacci(0) = 0 \nonumber \]

    \[ fibonacci(1) = 1 \nonumber \]

    \[ fibonacci(n) = fibonacci(n-1) + fibonacci(n-2) \nonumber \]

    Translated into Python, it looks like this:

    def fibonacci (n):
        if n == 0:
            return 0
        elif  n == 1:
            return 1
        else:
            return fibonacci(n-1) + fibonacci(n-2)
    

    If you try to follow the flow of execution here, even for fairly small values of n, your head explodes. But according to the leap of faith, if you assume that the two recursive calls work correctly, then it is clear that you get the right result by adding them together.


    This page titled 19.7: One More Example is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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