How can I show that the VC dimension of the set of all closed balls in $\mathbb{R}^n$ is at most $n+3$?

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How can I show that the VC dimension of the set of all closed balls in $\mathbb{R}^n$ is at most $n+3$?

For this problem, I only try the case $n=2$ for 1. When $n=2$, consider 4 points $A,B,C,D$ and if one point is inside the triangle formed by the other three, then we cannot find a circle that only excludes this point. If $ABCD$ is convex assume WLOG that $\angle ABC + \angle ADC \geq 180$ then use some geometric argument to show that a circle cannot include $A,C$ and exclude $B,D$.

For the general case I’m thinking of finding $n+1$ points so that a ball should be quite ‘large‘ to include them, and that this ball can not exclude the other 2 points. However, in high-dimensional case I do not know how to use maths language to describe what is ‘large’.

Can anyone give some ideas to this question please?

j200932

Posted 2020-01-16T13:25:46.480

Reputation: 181

1Hi and welcome to this community! I've noticed that you have asked several questions on this site and I really appreciate that, but you should not ask for solutions without even explaining what you have tried so far. You should also try to ask one question per post. I suggest you ask the first question in this post and create another post for the second question ;) – nbro – 2020-01-16T13:31:52.263

@nbro Thank you for your comment. I will edit my post. – j200932 – 2020-01-16T14:13:12.370

No answers