On Sun, Jul 5, 2020 at 8:57 PM Steven D'Aprano <st...@pearwood.info> wrote:
> On Sun, Jul 05, 2020 at 12:15:27PM -0400, David Mertz wrote: > > This is a digression, but does anyone have a nice example IN PYTHON of > > arriving at a NaN without going through infinity. I think Julia is right > > and Python is wrong about '0/0', but as things are, that's not an > example. > > I wouldn't expect one in Python, I think there is an unofficial policy > of ensuring that Python builtins and the math library will not return > NANs unless passed a NAN, or at least an INF, rather they will raise. > > > > >>> 1e1000-1e1000 > > > nan > is just a funny way of writing INF - INF :-) > The standard library *does* seem to have taken pains to avoid "finite nans." It kinda weakens your case about worrying about doing clamp() right in the face of NaNs :-). I recognize there are funny ways of writing infinity. But since Python really doesn't quite follow IEEE-754 on 0/0, or math.fmod(x, 0.), or a few other places it might arise in "natural" operations (i.e. it's easy not to notice that your 'y' has become zero. It also looks like the trig functions are pruned to those that don't have undefined values for numbers I can type in. I can *type* `math.tan(math.pi/2)`, of course. But math.pi is a little bit smaller than the actual pi, so I just get a big number for an answer. But I cannot try the hypothetical: >>> math.cot(0) nan For what we actually have: >>> math.tan(math.pi/2) 1.633123935319537e+16 One ULP more: >> math.tan(np.nextafter(math.pi/2, np.inf)) -6218431163823738.0 -- The dead increasingly dominate and strangle both the living and the not-yet born. Vampiric capital and undead corporate persons abuse the lives and control the thoughts of homo faber. Ideas, once born, become abortifacients against new conceptions.
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