Strange behaviour of function zero points

Stefan shared this question 10 months ago
Answered

I tinkered with some zooming in a function and found a rather strange behaviour.


I entered my function, used asymptote to find them, used "zero points" to mark them. Check the "ok" screenshot.


All is great until I zoom in a good bit. Then suddenly the zero points multiply themselves and are clearly graphed outside the curve. This happens if I scoll into the zoom, or if i select "zoom 400%" several times. Check the other screenshot, suddenly there are lots and lots of points.


Geogebra crashed on me then and I reopened it and re-entered the whole thing. Then, when I zoomed in the same thing happened.


Is this a bug or some behaviour I do not yet understand?

Comments (7)

photo
1

Please post your files and info about the GeoGebra version you've used to create them and your OS.

photo
1

My geogebra version is 6.0.542.0-win

My windows version is 10.0.17763.737


Btw. I just made this file from scratch using the functions from my screenshots, so this issue is reproducible on my computer.

photo
1

Both the file you have created here and the one in the screenshot have quite odd parameters in the Roots command, since you set as start and end point the same value.

e.g. Roots(f, 0.4, 0.5) works fine.


What I don't understand is that reopening your file on v.6 the guess interval for roots changes.

For example I now have this /gAAAABJRU5ErkJggg==

photo
1

Recreating your file from scratch doesn't have any problem, even when zooming in a lot.

But I've used (0.4, 0.5) as guess interval for the roots.

Also with a wider decimal approximation, I have no issues. See the attached file.

I think that the problem in your file is that you set the guess interval for the roots as a single point, instead of an interval.

Anyway, I'm looping this post to the devs, so they can have a look at it.

photo
2

I see it now.

I missed the fact that you used "Special points"option to get the roots.

In this case, zooming changes automatically the guess interval for roots. All the points are recalculated at every zoom action.

photo
2

Thanks, we'll check if we can improve this

photo
1

Just a heads up, this may be more involved. I created the attached file by typing in function f, selecting "extreme points" and "zero points" from the menu above, and using the f' and f'' typed in command to create those graphs and did the same point operations on them from the button menu above.


Now, whenever you click a graphed function off and on again via its color point, geogebra will add a new set of points for extreme and zero for that function, no matter f, f' or f''.


This example does not involve zooming, so I suspect the cause of both problems is in some call to "extreme points" or "zero points" whenever a function is redrawn, either by switching it on and off, or by zooming.


This would also explain why Simona could not reproduce the problem at first - an experienced user well versed in geogebra will probably type in commands they know by heart instead of using the menu.

Then again, I am not a programmer, so this is just a hunch. ;)

photo
© 2020 International GeoGebra Institute