CNiall schrieb:
I am very new to Python (I started learning it just yesterday), but I
have encountered a problem.
I want to make a simple script that calculates the n-th root of a given
number (e.g. 4th root of 625--obviously five, but it's just an example
:P), and because there is no nth-root function in Python I will do this
with something like x**(1/n).
However, with some, but not all, decimals, they do not seem to 'equal
themselves'. This is probably a bad way of expressing what I mean, so
I'll give an example:
>>> 0.5
0.5
>>> 0.25
0.25
>>> 0.125
0.125
>>> 0.2
0.20000000000000001
>>> 0.33
0.33000000000000002
As you can see, the last two decimals are very slightly inaccurate.
However, it appears that when n in 1/n is a power of two, the decimal
does not get 'thrown off'. How might I make Python recognise 0.2 as 0.2
and not 0.20000000000000001?
This discrepancy is very minor, but it makes the whole n-th root
calculator inaccurate. :\
Welcome to the wonderful world of IEEE754. Just because other languages
shield you from the gory details they still are there. Python chose to
not do that, instead showing the rounding errors introduced and making
the developer decide how to deal with these.
http://pyfaq.infogami.com/why-are-floating-point-calculations-so-inaccurate
Diez
--
http://mail.python.org/mailman/listinfo/python-list
