2010/7/30 Guillaume Chérel <guillaume.c.che...@gmail.com>: > > Hello, > > I ran into a difficulty with floating point arithmetic in python. Namely > that: > > >>> 0.001 + 1 - 1 > 0.00099999999999988987 > > And, as a consequence, in python: > > >>> 0.001 + 1 - 1 == 0.001 > False > > In more details, my problem is that I have a fonction which needs to > compute (a + b - c) % a. And for b == c, you would expect the result to > be 0 whatever the value of a. But it isn't... > > >>> (0.001 + 1 - 1) % 0.001 > 0.00099999999999988987 > > Is there any way to solve this?
One simple way is to put brackets round the integer subtraction, >>> 0.001 + 1 - 1 == 0.001 False >>> 0.001 + (1 - 1) == 0.001 True However, in general comparing floating point numbers is tricky and a complex issue in numerical computing. This is not a Python or NumPy specific problem ;) Peter _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
