Approximating the spanning star forest problem and its applications to genomic sequence alignment

This paper studies the algorithmic issues of the spanning star forest problem. We prove the following results: (1) there is a polynomial-time approximation scheme for planar unweighted graphs; (2) there is a polynomial-time algorithm with approximation ratio 3/5 for unweighted graphs; (3) it is NP-hard to approximate the problem within ratio 545/546 + ε for unweighted graphs; (4) there is a linear-time algorithm to compute the maximum star forest of a weighted tree; (5) there is a polynomial-time algorithm with approximation ratio 1/2 for weighted graphs. We also show how to apply this spanning star forest model to aligning multiple genomic sequences over a tandem duplication region.