Reconstructing Polyatomic Structures from Discrete X-Rays: NP-Completeness Proof for Three Atoms
<|reference_start|>Reconstructing Polyatomic Structures from Discrete X-Rays: NP-Completeness Proof for Three Atoms: We address a discrete tomography problem that arises in the study of the atomic structure of crystal lattices. A polyatomic structure T can be defined as an integer lattice in dimension D>=2, whose points may be occupied by $c$ distinct types of atoms. To ``analyze'' T, we conduct ell measurements that we call_discrete X-rays_. A discrete X-ray in direction xi determines the number of atoms of each type on each line parallel to xi. Given ell such non-parallel X-rays, we wish to reconstruct T.   The complexity of the problem for c=1 (one atom type) has been completely determined by Gardner, Gritzmann and Prangenberg, who proved that the problem is NP-complete for any dimension D>=2 and ell>=3 non-parallel X-rays, and that it can be solved in polynomial time otherwise.   The NP-completeness result above clearly extends to any c>=2, and therefore when studying the polyatomic case we can assume that ell=2. As shown in another article by the same authors, this problem is also NP-complete for c>=6 atoms, even for dimension D=2 and axis-parallel X-rays. They conjecture that the problem remains NP-complete for c=3,4,5, although, as they point out, the proof idea does not seem to extend to c<=5.   We resolve the conjecture by proving that the problem is indeed NP-complete for c>=3 in 2D, even for axis-parallel X-rays. Our construction relies heavily on some structure results for the realizations of 0-1 matrices with given row and column sums.<|reference_end|>
@article{durr1999reconstructing,
    title={Reconstructing Polyatomic Structures from Discrete X-Rays:
  NP-Completeness Proof for Three Atoms},
    author={Christoph Durr and Marek Chrobak},
    journal={Proceedings of the 23rd International Symposium on Mathematical
  Foundations of Computer Science, LNCS vol 1450, 185-193, 1998},
    year={1999},
    archivePrefix={arXiv},
    eprint={cs/9906018},
    primaryClass={cs.DS cs.CC}
}