LocusEquation doesn't work for circle under affine transformation

m93a shared this problem 3 years ago
Not a Problem

I created a affine transformation defined by an axis, a point A and its image A'. Then I added a pre-image circle, defined a point X on it and then constructed its image X'. When I use


  1. Locus[X',X]

it works fine and I get a fine ellipse, but when I do


  1. LocusEquation[X',X]

GeoGebra freezes for some time, then it either crashes or gives me a nonsense parabola or something.


I'm using GeoGebra 5.0.355.0-3D.

Comments (10)

photo
1

Sorry, your file doesn't seem to be available. Try reattaching without a <space> in the filename

photo
1

Does this work?

photo
2

locus equation allows only geometric objects; not numbers, Axis, etc

change the xAxis with another line created with free points like in attached file

are you sure that the transformation is affine? if yes then there is a bug in locus equation because the locus must be an ellipse (no cubic)

photo
1

now the attached gives error

I do not know why

photo
photo
2

the bug is the same bug of this old post

https://help.geogebra.org/t...

in this case the line AA' is in the locusequation (more thickness shows)

I think the right answer must be d in attached

photo
1

the attached files dissapear

sometimes I spend three or four times for opening (FF)

photo
photo
1

I'm positive, it is an axial affinity. Here you can see the construction I've used. Although this construction is quite common in Czech and Slovak descriptive geometry classes, it seems that the rest of the world doesn't use it much. Weird...


You're right, using line instead of axis partially fixes the problem – however axes are lines and should be treated like ones! What bothers me more is that the redundant line makes it (almost) impossible to use tangents and all the other conic stuff.

photo
1

why do you think impossible to use tangents?

see k in attached

you can not to use aXis because locusequation uses only your geometric objects and the aXis is not created by you

photo
1

Ok, when using custom lines instead of axes, it kinda works, but are you sure this can question be marked as not a problem? Wouldn't it be better to actually fix it and make LocusEquation treat axes as lines? Or at least document this behavior?

And it's impossible to use tangents because if there's a huge straight thing sticking out of your hyperbola, the Tangent function obviously gives a bit different answers then if the hyperbola would be... you know, just a hyperbola.

photo
1

Have you read through all the documentation?


http://wiki.geogebra.org/en...

© 2021 International GeoGebra Institute