@InProceedings{Tilt_ICRA2014,
AUTHOR = {Aaron Becker and Erik D. Demaine and S\'andor Fekete and James McLurkin},
TITLE = {Particle Computation: Designing Worlds to Control Robot Swarms with Only Global Signals},
BOOKTITLE = {Proceedings of the 2014 IEEE International Conference on Robotics and Automation (ICRA 2014)},
bookurl = {http://www.icra2014.com/},
ADDRESS = {Hong Kong, China},
MONTH = {May 31--June 7},
YEAR = 2014,
PAGES = {6751--6756},
doi = {https://dx.doi.org/10.1109/ICRA.2014.6907856},
dblp = {https://dblp.org/rec/conf/icra/BeckerDFM14},
comments = {The paper is available as
<A HREF="http://arxiv.org/abs/1402.3749">
arXiv.org:1402.3749</A> of the
<A HREF="http://arXiv.org/archive/cs/intro.html">
Computing Research Repository (CoRR)</A>, and from <A HREF="https://doi.org/10.1109/ICRA.2014.6907856">IEEE</A>.},
}
In previous work we proved it is NP-hard to decide whether a given initial configuration can be transformed into a desired target configuration; in this paper we prove a stronger result: the problem of finding an optimal control sequence is PSPACE-complete. On the positive side, we show we can build useful systems by designing obstacles. We present a reconfigurable hardware platform and demonstrate how to form arbitrary permutations and build a compact absolute encoder. We then take the same platform and use dual-rail logic to build a universal logic gate that concurrently evaluates AND, NAND, NOR and OR operations. Using many of these gates and appropriate interconnects we can evaluate any logical expression.