(x-1)/(x+1)

[carlosmintfan]

Hi @mauriciopoppe, thank you for this library! Would like to share this amazing, but probably buggy representation of (x-1)/(x-1):

What's that?! Very funny. Beautiful, super interesting, this design! But I think it comes out of a bug? I think the solution line should always be y = 1, not getting bold between 0.3 (or so) and 1 already and turning into two lines that then flow at 0.99 into infinity, then come back and get one line on the right again? Wow, this is awesome. But if we want to represent the function correctly, the solution should always be y = 1, only at exactly x = 1 there is no solution, but on plotters like graph.equation.io that's invisible.

Is this some fascinating intrinsic of your interval-arithmetic math?

Somewhat the opposite is happening when plotting tan(x). Then graph.equation.io prints vertical lines where the tangent is undefined, your plotter is “cleaner” and doesn't! How is that?

[mauriciopoppe]

Yes, this is indeed because of interval arithmetic. I've been collecting all the issues related with how interval arithmetic works and its quirks (you found one!). The reason is that there's error carried during interval division. I'm planning on writing a more detailed example in the docs or my blog soon, in the meantime, please change your datum to the following:

{  fn: '(x-1)/(x-1)', graphType: 'polyline' }

[carlosmintfan]

Thank you! Now there‘s a line at y = 1, but when then moving my fingers around on the canvas (on a touchscreen) on https://mauriciopoppe.github.io/function-plot/, I get the Codesandbox Error Overlay: TypeError: The provided value is non-finite.
Can you reproduce this?
Lol. But I don’t need a quick workaround, I’m not using this in any production project, just experimenting!

[carlosmintfan]

The original issue looks like being exactly the same one as #232 (which shouldn’t have been closed lol)