# Radius of a circle becomes 0

rgruber shared this problem 10 years ago

There is a difference between version 3.2 an newer versions (3.2.45.10):

Existing a slider (r) for real numbers between 0 and 5;

a line with a point (A) on it;

a circle with midpoint A and Radius r;

intersection point (C) of the line and the circle.

If the radius becomes 0, the intersection point (C)

* does not exist longer in the newer versions, but it

* does exit in version 3.2

So a few constructions working in 3.2 do not work in the new versions.

1

May be ...

the value was not yet exactly zero? If it was only rounded to zero the intersection point could still excist ... just an idea :confused:

Birgit

1

1

The file "KreisRadiusNull.ggb" works correctly. If I drag the slider (r) to 0, the point C exists furthermore. This is what you will expect.

When I start the file "Würfelschnitt.ggb" and I drag the point E''' to an end of the arc, the pictures are not complete; parts of the elevation and as a result of it parts of the 'Schrägriss' (in german) vanish. This was the point, when I found this problem. I did the construction in version 3.2 at home. When I showed it to my students working under a newer version, the problem occurs.

Now:

I hope, you can reproduce the problem.

Greetings Rudi

https://ggbm.at/546603

1

It's a problem in your construction I think:

C''=Intersect[f_1, e_1, 2]

When f_1 has zero radius, there is no second intersection point so C'' becomes undefined.

You could try something like:

If[IsDefined[C''], C'', Intersect[f_1, e_1, 1]]

1

Thank you.

I use instead of the compass now a vectoraddition and it works fine.

Rudi