RT Monograph SR 00 A1 Gondzio, J. A1 Makowski, M. T1 HOPDM Modular Solver for LP Problems User's Guide to version 2.12 YR 1995 FD 1995-06 SP 25 AB The paper provides a description of HOPDM, a library of routines for solving large scale linear programming problems and its implementation at IIASA. HOPDM stands for Higher Order Primal Dual Method. The algorithm implemented in HOPDM is a new variant of a primal-dual logarithmic barrier method that uses multiple correctors of centrality. The newest version of the library -- HOPDM 2.12 -- is a robust and efficient LP code that compares favorably with the up to date commercial solvers. The paper contains an outline of the algorithm implemented in HOPDM and information about results of tests done with large LP problems developed at IIASA. Finally, the paper provides with details of the implementation of HOPDM and its use at IIASA, as well as with information about availability of the portable version of the HOPDM library. PB WP-95-050 PP IIASA, Laxenburg, Austria AV Published LK https://pure.iiasa.ac.at/id/eprint/4542/