Intersect for hyperbola and arc switches variables

Memorial shared this problem 3 years ago

When using Intersect[] for a circular arc and a hyperbola, the points of intersection change to new variables with relatively minor movements of the arc defining points. I speculate this has something to do with the way that points of intersection of the complete circle and the hyperbola are ordered, but it seems to be that intersection variables shouldn't change under small deformation.

To replicate: in the attached .gbb file, drag the point B vertically up. You will see the points F,E change to new points H,G with F,E becoming undefined.

OS: OS X 10.11.4 Beta

GeoGebra (29 January 2016) Java: 1.8.0_20

Comments (2)



Try setting Options>>Advanced Preferences>>Continuity to "On".

Continuity: if Continuity is On, GeoGebra tries to set new calculated points near the original ones




Intersect is a beast to tame. A very knowledgeable and helpful person in this forum at one time suggested for the result of the intersect command to be placed in a list like this:

    { Intersect[<your parameters here>] }

That was a very useful suggestion, particularly when combined with RemoveUndefined and Unique. That way the results of Intersect tend to be more manageable and predictable. Basically, something along the lines of:

    YourIntersectionList = Unique[RemoveUndefined [{ Intersect[<your parameters here>] }]]

Hopefully the above will be useful to you,


© 2019 International GeoGebra Institute