On Jan 13, 2015, at 6:58 PM, Ron Adam
wrote: maybe we could specify an absolute tolerance near zero, and a relative tolerance elsewhere, both at once. Tricky to document, even if possible.
Doesn't this problem come up at any boundary comparison, and not just zero?
Zero is special because you lose the ability to use a relative tolerance. Everything is huge compared to zero.
So isn't the issue about any n distance from any floating point number that is less than 1 ulp?
I'm still a bit fuzzy on Ulps, but it seems the goal here is to define a tolerance larger than an ulp. This is for the use case where we expect multiple rounding errors -- many more than one ulp, That's why I think the use case for ulp comparisons is more about assessment of accuracy of algorithms than "did I introduce a big old bug?" or, "is this computed value close enough to what I measured?" -Chris