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We present new approximation algorithms for several facility location problems. In each facility location problem that we study, there is a set of locations at which we may build a facility (such as a warehouse), where the cost of building at location i is ~i; ftier-more, there is a set of client locations (such as stores) that require to be serviced by a(More)
Wireless communication is used in many different situations such as mobile telephony, radio and TV broadcasting, satellite communication, and military operations. In each of these situations a frequency assignment problem arises with application specific characteristics. Researchers have developed different modeling ideas for each of the features of the(More)
We consider the polyhedral approach to solving the capacitated facility location problem. The valid inequalities considered are the knapsack, ow cover, eeective capacity, single depot, and combinatorial inequalities. The ow cover, eeective capacity, and single depot inequalities form subfamilies of the general family of submodular inequalities. The(More)
On August 22, 1999, we completed the factorization of the 512{bit 155{digit number RSA{155 with the help of the Number Field Sieve factoring method (NFS). This is a new record for factoring general numbers. Moreover, 512{bit RSA keys are frequently used for the protection of electronic commerce|at least outside the USA|so this factorization represents a(More)
In this survey we address three of the principal algebraic approaches to integer programming. After introducing lattices and basis reduction, we ÿrst survey their use in integer programming, presenting among others Lenstra's algorithm that is polynomial in ÿxed dimension, and the solution of diophanine equations using basis reduction. The second topic(More)
In the k-level uncapacitated facility location problem, we have a set of demand points where clients are located. The demand of each client is known. Facilities have to be located at given sites in order to service the clients, and each client is to be serviced by a sequence of k different facilities, each of which belongs to a distinct level. There are no(More)
We study the two-level uncapacitated facility location (TUFL) problem. Given two types of facilities, which we call y-facilities and z-facilities, the problem is to decide which facilities of both types to open, and to which pair of y-and z-facilities each client should be assigned, in order to satisfy the demand at maximum proot. We rst present two(More)