README.md

Constrained Smallest Enclosing Ball Algorithm

CMB (Constrained Mini Ball) is a C++ library to compute minimum bounding balls with affine constraints on the centre of the ball. CMB implements a modified version of Emo Welzl's Miniball algorithm [1].

Given $X = {x_1, \ldots, x_n} \subset \mathbb{R}^d$ and an affine subspace $E \subset \mathbb{R}^d$, we wish to find

$$\mathrm{argmin}_{z \in E} \ \max \{\| z - x_1\|_2, \ldots, \|z - x_n\|_2 \}$$

i.e., the centre of the smallest bounding ball of $X$ whose centre is constrained to lie in $E$.

The problem can be solved in amortized $O(n)$ time by using Welzl's algorithm, with a modification of the terminating condition of Welzl's algorithm.

Installation and requirements

CMB is provided as a single header-only library cmb.hpp, and requires

• C++20 compliant compiler with support for concepts (GCC 10.3, Clang 10, MSVC 2019 16.3 or later versions of these compilers).
• The Eigen C++ library (tested with version 3.4.0).
• The Computational Geometry Algorithms Library (tested with version 5.6.0).
• The GNU Multiple Precision library (tested with version 6.2.1).

Example usage

See example.cpp for examples.

Running the tests

The tests in the test folder can be built with CMake by running cmake . && cmake --build in the root folder. The resulting test program will be in the build folder under the name runtests.

License

Copyright (c) 2023 Abhinav Natarajan.

ConstrainedMiniball is released under the GNU General Public License ("GPL").

References

[1] E. Welzl, “Smallest enclosing disks (balls and ellipsoids),” in New Results and New Trends in Computer Science, H. Maurer, Ed., in Lecture Notes in Computer Science. Berlin, Heidelberg: Springer, 1991, pp. 359–370. doi: 10.1007/BFb0038202.