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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