Is there a simple algorithm to check whether $n$ different balls (of the same radius) in $\mathbb{R}^d$ intersect? That is, coordinates of their centers $x_i$ are given, radius $R$ is given and we need to determine if there exists a point $p$ such that $$\| p - x_i \| \leq R \quad \forall i.$$ In other words, check whether there is a point $p$ that is contained in all $n$ balls.

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    $\begingroup$ related? cs.stackexchange.com/questions/23942/… $\endgroup$
    – guest
    Nov 5, 2017 at 18:20
  • $\begingroup$ Right now I am using $\| \cdot \|_{\infty}$ for simplicity, in this case it is just a collection of $1$d checks. For the euclidiean norm I was thinking about writing an optimization problem and checking its feasibility using some optimizer. $\endgroup$
    – Mathemage
    Nov 5, 2017 at 19:51

1 Answer 1


This is an instance of the smallest enclosing ball problem.

An equivalent statement of your problem is: Given points $x_1,\dots,x_n$, we want to determine whether there exists a point $p$ such that every point $x_i$ is at distance at most $R$ from $p$, i.e., we want to find a sphere of radius $R$ that encloses all of the points $x_1,\dots,x_n$.

So, find the smallest enclosing ball that contains all of $x_1,\dots,x_n$; then check whether the radius of that ball is at most $R$ or not. The smallest enclosing ball problem is well-studied and you can find references and algorithms in the Wikipedia page I linked to.


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