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Re: Throw the cat among the pigeons

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Op Tuesday 5 May 2015 20:45 CEST schreef Dave Angel:

> On 05/05/2015 12:18 PM, Cecil Westerhof wrote:
>
>>
>> Well, I did not write many tail recursive functions. But what
>> surprised me was that for large values the ‘tail recursive’ version
>> was more efficient as the iterative version. And that was with
>> myself implementing the tail recursion. I expect the code to be
>> more efficient when the compiler implements the tail recursion.
>>
>
>
> You've said that repeatedly, so I finally took a look at your
> webpage
>
> https://github.com/CecilWesterhof/PythonLibrary/blob/master/mathDecebal.py
>
> I didn't have your framework to call the code, so I just extracted
> some functions and did some testing.

I definitely need to take care of documentation.

It can be called with:
    python3 mathDecebal.py --factorial

The problem is that it will do correctness and speed test. I have to
split those in two different things. And use a different file for
both.

Maybe make a directory test and put a correctness_<function>.py and a
speed_<function>.py.



> I do see some differences,
> where the so-called tail_recursive functions are sometimes faster,
> but I did some investigating to try to determine why.
>
>
> I came up with the conclusion that sometimes the multiply operation
> takes longer than other times.  And in particular, i can see more
> variation between the two following loops than between your two
> functions.
>
>
> def factorial_iterative(x, simple=False):
> assert x >= 0
> result = 1
> j=2
> if not simple:
> for i in range(2, x + 1):
> result *= i
> j += 1
> else:
> for i in range(2, x + 1):
> result *= j
> j += 1
> pass
>
> return result
>
> When the "simple" is True, the function takes noticeably and
> consistently longer.  For example, it might take 116 instead of 109
> seconds.  For the same counts, your code took 111.
>
> I've looked at dis.dis(factorial_iterative), and can see no explicit
> reason for the difference.

I would say that a variable that is filled by a range is different as
a normal variable. Do not ask me why. ;-)

Even if you (general not personal you) think that the tail recursion
is a waist of time, this is an interesting result I think.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

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Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-02 16:20 +0200
  Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-03 17:12 +0200
    Re: Throw the cat among the pigeons Paul  Moore <p.f.moore@gmail.com> - 2015-05-05 08:47 -0700
      Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 18:18 +0200
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 14:45 -0400
          Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 21:42 +0200
            Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 12:57 +1000
              Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-06 14:03 +1000
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 14:30 -0600
        Re: Throw the cat among the pigeons Terry Reedy <tjreedy@udel.edu> - 2015-05-05 16:46 -0400
          Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 23:12 +0200
            Re: Throw the cat among the pigeons Terry Reedy <tjreedy@udel.edu> - 2015-05-05 19:22 -0400
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 17:00 -0400
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 15:23 -0600
          Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 11:27 +1000
            Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 23:58 -0600
              Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 17:08 +1000
                Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-06 10:17 -0600
                Re: Throw the cat among the pigeons Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-06 21:23 +0100
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 15:39 -0600
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 17:55 -0400
        Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 12:19 +1000
  Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 14:05 +1000
    Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 16:26 +1000
      Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 09:12 -0400
        Re: Throw the cat among the pigeons Dan Sommers <dan@tombstonezero.net> - 2015-05-07 03:16 +0000
      Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-06 23:55 +1000
      Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 10:22 -0400
      Re: Throw the cat among the pigeons Paul Rubin <no.email@nospam.invalid> - 2015-05-06 08:12 -0700
        Re: Throw the cat among the pigeons Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-05-06 17:36 +0200
          Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 16:23 -0400
            Re: Throw the cat among the pigeons Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-05-07 11:14 +0200
              Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-07 19:38 +1000
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-06 09:47 -0600
          Re: Throw the cat among the pigeons Paul Rubin <no.email@nospam.invalid> - 2015-05-06 10:24 -0700

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