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Re: Fibonacci series recursion error

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On Mon, May 2, 2011 at 3:50 PM, harrismh777 <harrismh777@charter.net> wrote:
> Thomas Rachel wrote:
>>>
>>> ... because each recursion level 'return' calls fib() twice, and each of
>>> those calls fib() twice, and you get the point...
>>
>> yes - but they are called one after the other, so the "twice" call
>> counts only for execution speed, not for recursion depth.
>
>>>> def fib(n):
>>>>     if n == 1:
>>>>         return(n)
>>>>     else:
>>>>         return (fib(n-1)+fib(n-2))
>
> They *are not* called one after the other in the sense that there is ever
> only one level of recursion with each call (not at all). Take a closer look.
> Each call to fib() forces a double head, and each of those forces another
> double head (now four), and so on...

The branching factor has nothing to do with the maximum stack depth.
If you don't believe me, consider this little script:

import inspect
def maxstack(n):
    if n <= 0:
        return len(inspect.stack())
    else:
        return max(maxstack(n-1), maxstack(n-2))
print maxstack(15)

This prints "17".

Now consider this script, which is similar but singly-recursive:

import inspect
def maxstack(n):
    if n <= 0:
        return len(inspect.stack())
    else:
        return maxstack(n-1)
print maxstack(15)

This also prints "17".  Note: they're the same.

>  the recursion depth exception of the
> OP testifies against your theory.

The OP's recursion depth exception was because a malformed base case
made the recursion infinite.  It had nothing to do with the branching
factor.

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Fibonacci series recursion error lalit <opposite800@gmail.com> - 2011-04-29 20:22 -0700
  Re: Fibonacci series recursion error Gary Herron <gherron@islandtraining.com> - 2011-04-29 20:41 -0700
  Re: Fibonacci series recursion error Jason Friedman <jason@powerpull.net> - 2011-04-30 03:57 +0000
  Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-04-29 23:45 -0500
    Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-04-29 23:51 -0500
      Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-04-30 00:31 -0500
        Re: Fibonacci series recursion error Peter Otten <__peter__@web.de> - 2011-04-30 08:14 +0200
          Re: Fibonacci series recursion error rusi <rustompmody@gmail.com> - 2011-05-02 00:08 -0700
    Re: Fibonacci series recursion error Hans Georg Schaathun <hg@schaathun.net> - 2011-04-30 06:50 +0100
    Re: Fibonacci series recursion error Paul Rudin <paul.nospam@rudin.co.uk> - 2011-04-30 06:43 +0100
  Re: Fibonacci series recursion error Ian Kelly <ian.g.kelly@gmail.com> - 2011-04-29 23:27 -0600
    Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-04-30 00:35 -0500
      Re: Fibonacci series recursion error Peter Otten <__peter__@web.de> - 2011-04-30 08:32 +0200
        Re: Fibonacci series recursion error Chris Angelico <rosuav@gmail.com> - 2011-04-30 16:37 +1000
      Re: Fibonacci series recursion error Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-04-30 11:37 +0200
        Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-05-02 16:50 -0500
          Re: Fibonacci series recursion error Chris Angelico <rosuav@gmail.com> - 2011-05-03 08:17 +1000
            Re: Fibonacci series recursion error harrismh777 <harrismh777@charter.net> - 2011-05-03 12:10 -0500
              Re: Fibonacci series recursion error Chris Angelico <rosuav@gmail.com> - 2011-05-04 07:41 +1000
              Re: Fibonacci series recursion error Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-03 16:31 -0600
              Re: Fibonacci series recursion error Chris Angelico <rosuav@gmail.com> - 2011-05-04 09:09 +1000
          Re: Fibonacci series recursion error Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-02 16:22 -0600
          Re: Fibonacci series recursion error Chris Angelico <rosuav@gmail.com> - 2011-05-03 08:42 +1000
          Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-02 18:48 -0700
            Re: Recursion or iteration (was Fibonacci series recursion error) Chris Angelico <rosuav@gmail.com> - 2011-05-03 12:13 +1000
            Re: Recursion or iteration (was Fibonacci series recursion error) Chris Angelico <rosuav@gmail.com> - 2011-05-03 15:29 +1000
              Re: Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-03 00:52 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Dave Angel <davea@ieee.org> - 2011-05-03 06:32 -0400
                Re: Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-03 03:51 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Chris Angelico <rosuav@gmail.com> - 2011-05-03 21:04 +1000
                Re: Recursion or iteration (was Fibonacci series recursion error) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-03 12:49 +0000
                Re: Recursion or iteration (was Fibonacci series recursion error) Chris Angelico <rosuav@gmail.com> - 2011-05-03 23:02 +1000
                Re: Recursion or iteration (was Fibonacci series recursion error) Hans Mulder <hansmu@xs4all.nl> - 2011-05-12 00:06 +0200
                Re: Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-13 04:11 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-13 07:55 -0600
                Re: Recursion or iteration (was Fibonacci series recursion error) Hans Mulder <hansmu@xs4all.nl> - 2011-05-13 21:46 +0200
                Re: Recursion or iteration (was Fibonacci series recursion error) Mark Dickinson <dickinsm@gmail.com> - 2011-05-13 14:48 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-14 10:24 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-14 15:19 -0600
                Re: Recursion or iteration (was Fibonacci series recursion error) rusi <rustompmody@gmail.com> - 2011-05-14 20:32 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Mark Dickinson <dickinsm@gmail.com> - 2011-05-15 12:20 -0700
                Re: Recursion or iteration (was Fibonacci series recursion error) Mark Dickinson <dickinsm@gmail.com> - 2011-05-15 12:29 -0700
            Re: Recursion or iteration (was Fibonacci series recursion error) Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-02 23:46 -0600

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