[Numpy-discussion] Dealing with roundoff error

Mike Sarahan msarahan@gmail....
Sat Mar 27 18:38:27 CDT 2010


Hi all,

I have run into some roundoff problems trying to line up some
experimental spectra.  The x coordinates are given in intervals of 0.1
units.  I read the data in from a text file using np.loadtxt().

I think Robert's post here explains why the problem exists:
http://mail.scipy.org/pipermail/numpy-discussion/2007-June/028133.html

However, even linspace shows roundoff error:

a=np.linspace(0.0,10.0,endpoint=False)
b=np.linspace(0.1,10.1,endpoint=False)
np.sum(a[1:]==b[:-1])  # Gives me 72, no 100

What is the best way to deal with it?  Multiply the intervals by 10,
then convert them to ints?

Thanks,
Mike


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