On Tue, Feb 22, 2011 at 8:20 AM, christian schulze <xcr...@googlemail.com> wrote: > Hey guys, > > I just found out, how much Python fails on simple math. I checked a > simple equation for a friend. > > [code] >>>> from math import e as e >>>> from math import sqrt as sqrt >>>> 2*e*sqrt(3) - 2*e == 2*e*(sqrt(3) - 1) > False > [/code] > > So WTF? The equation is definitive equivalent. (See http://mathbin.net/59158) > > PS: > > #1: >>>> 2.0 * e * sqrt(3.0) - 2.0 * e > 3.9798408154464964 > > #2: >>>> 2.0 * e * (sqrt(3.0) -1.0) > 3.979840815446496 > > I was wondering what exactly is failing here. The math module? Python, > or the IEEE specifications? >
1 / 3 = 0.33333333333 1 / 3 * 3 = 0.333333333 * 3 = 0.999999999 != 1 OMG MATH IS BROKEN!!!!!!!!!!!!!!! Unless you're doing symbolic manipulation or have infinite precision, it's impossible to accurately represent most values. In fact, e is not really e, it's just the closest approximation to e we can get using 64 bits. So the exact amount it's off is a result of IEEE. The fact that it's off at all is a result of us not having infinite memory. -- http://mail.python.org/mailman/listinfo/python-list
