RELIABILITY OF ITERATIVE LINEAR-EQUATION SOLVERS IN CHEMICAL PROCESS SIMULATION

For large-scale problems, it may be attractive to use iterative method s to solve the large, sparse, linear systems that arise in the equatio n-based approach to process simulation. This is because, as problem si zes grow, direct methods become extremely expensive in terms of both c omputation time and storage requirements. Iterative methods, however, may not be reliable for the indefinite and highly unsymmetric matrices encountered in a diverse multi-unit flowsheeting problem. An extensiv e computational study of the reliability of iterative linear solvers o n such problems is presented here. Nine different iterative linear sol vers are considered, in connection with incomplete factorization preco nditioning. These are applied to a set of nine test problems. Results indicate that the ordering of rows and columns in the matrices is a cr ucial factor in determining the success with which iterative methods c an be employed. Results also indicate that in general these multi-unit flowsheeting matrices are difficult to solve by iterative methods, an d that, though there is certainly potential in the use of iterative me thods, to realize this potential will require improvements in the reor dering and/or preconditioning schemes used. (C) 1996 Elsevier Science Ltd