neal young / Kolliopoulos05Approximation

Journal of Computer and System Sciences 71(4):495505(2005); FOCS'01Given matrices A and B and vectors a, b, c and d, all with nonnegative entries, we consider the problem of minimizing c$\cdot$x subject to x$\in Z^n_+$, Ax ≥ a, Bx ≤ b, and x ≤ d. We give a bicriteriaapproximation algorithm that, given ε$\in$(0, 1], finds a solution of cost O(log(m)/ε^{2}) times optimal, meeting the covering constraints Ax≥a and multiplicity constraints (x≤d), and satisfying Bx≤(1 + ε)b + β, where β is the vector of row sums, β_i=$\sum_j$ B_{ij}. Here m is the number of rows of A.
This gives an O(log m)approximation algorithm for CIP  minimumcost covering integer programs with multiplicity constraints, i.e., the special case when there are no packing constraints Bx ≤ b. The previous best approximation ratio has been O(log max_{j} $\sum_i$A_{ij} since 1982. CIP contains the set cover problem as a special case, so O(log m)approximation is the best possible unless P=NP.Journal version of Tight approximation results for general covering integer programs.
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