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 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.
--
DaveA
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