# Alexandru Popa

## Algorithmic and Hardness Results for the Colorful Components Problems

VCLA and TU Wien International Office will host a talk by Alexandru Popa on July 7, 2015

DATE: | Tuesday, July 7, 2015 |

TIME: | 14:00 |

VENUE: | Seminarroom E186 (Favoritenstrasse 9-11, 5th floor) |

**ABSTRACT**

We investigate the colorful components framework, motivated by applications emerging from comparative genomics. The general goal is to remove a collection of edges from an undirected vertex-colored graph G such that in the resulting graph G′ all the connected components are colorful (i.e., any two vertices of the same color belong to different connected components). We want G′ to optimize an objective function, the selection of this function being specific to each problem in the framework. We analyze three objective functions, and thus, three different problems, which are believed to be relevant for the biological applications: minimizing the number of singleton vertices, maximizing the number of edges in the transitive closure, and minimizing the number of connected components. Our main result is a polynomial-time algorithm for the first problem. This result disproves the conjecture of Zheng et al. that the problem is NP-hard (assuming P ≠ NP). Then, we show that the second problem is APX-hard, thus proving and strengthening the conjecture of Zheng et al. that the problem is NP-hard. Finally, we show that the third problem does not admit polynomial-time approximation within a factor of |V|1/14 − ε for any ε > 0, assuming P ≠ NP (or within a factor of |V|1/2 − ε , assuming ZPP ≠ NP). The talk is based on three papers: a paper from LATIN 2014, a journal paper at Algorithmica and another paper at IWOCA 2014. [Slides]