On 01/23/2015 01:30 PM, Nathaniel Smith wrote:
On Fri, Jan 23, 2015 at 12:40 AM, Chris Barker wrote:
So for reference, it looks like the differences from numpy are:
1) kwarg names: "tol" and "abs_tol" versus "atol", "rtol". Numpy's names seem fine to me, but if you want the longer ones then probably "rel_tol", "abs_tol" would be better?
Longer names are good for us non-maths folks. ;) rel_tol and abs_tol look good to me.
2) use of max() instead of + to combine the relative and absolute tolerance. I understand that you find the + conceptually offensive, but I'm not really sure why -- max() is maybe a bit better, but it seems like much of a muchness to me in practice. (Sure, like you say further down, the total error using + might end up being higher by a factor of two or so -- but either people are specifying the tolerances they want, in which case they can say what they mean either way, or else they're just accepting the defaults, in which case they don't care.) It might be worth switching to + just for compatibility.
That makes no sense to me. I'm not sure taking the max does either, though, as phrases like "you can be off by 5% or 30 units, whichever is [smaller | greater]" comes to mind.
One option would be to add a zero_tol argument, which is an absolute tolerance that is only applied if expected == 0.
Seems reasonable.
I'd strongly consider expanding the scope of this PEP a bit so that it's proposing both a relative/absolute-error-based function *and* a ULP-difference function. There was a plausible-looking one using struct posted in the other thread, it would cover a wider variety of cases, and having both functions next to each other in the docs would provide a good opportunity to explain why the differences and which might be preferred in which situation.
Also seems reasonable. So, in the interest of keeping things insane ;) how about this signature? def close_to(noi, target, min_tol, max_tol, rel_tol, zero_tol): """ returns True if noi is within tolerance of target noi: Number Of Interest - result of calulations target: the number we are trying to get min_tol: used with rel_tol to determine actual tolerance max_tol: used with rel_tol to determine actual tolerance zero_tol: an absolute tolerance if target == 0 (otherwise rel_tol is used an as zero_tol) """ -- ~Ethan~