[Numpy-discussion] floating point arithmetic issue

Guillaume Chérel guillaume.c.cherel@gmail....
Fri Jul 30 05:45:47 CDT 2010


  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?

Many thanks,
Guillaume


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