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Dr. Ibaraki’s χMD is more robust, faster and more efficient than its predecessor. The preconditioning module of χMD consisting of level-based incomplete LU (ILU) factorization with a drop tolerance scheme reduces memory usage and decreases the execution time. The acceleration consists of the conjugate gradient method, Bi-CGSTAB and ORTHOMIN. Reducing memory usage by a factor of two or more and decreasing execution times by 40% or more, χMD is now widely used as the predominant matrix solver in MODFLOW.