[Numpy-discussion] commutative allclose
Tom Johnson
tjhnson@gmail....
Thu Apr 10 14:56:44 CDT 2008
Should allclose() be commutative, so as to prevent the following:
>>> x = 1.00001001
>>> allclose(x,1), allclose(1,x)
(False, True)
There is some discussion here which provides two possible solutions:
http://www.boost.org/doc/libs/1_35_0/libs/test/doc/components/test_tools/floating_point_comparison.html
Notice, the discussion states that their solutions are not
transitive---nevertheless, I think commutativity is a worthwhile
improvement. Also, they mention that rtol * abs(y) can cause
underflow issues. Thus, they implement,
|x-y|/|y| <= rtol AND(OR) |x-y|/|x| <= rtol
without an atol option, rather than
|x-y| <= atol + rtol* |y|
Naively, it seems like atol is attempting to correct this very issue.
So do we really need atol?
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