NAG Fortran Library Routine Document F11DAF
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The argument PSTRAT defines the pivoting strategy to be used. The options currently available are no pivoting, user-defined pivoting, partial pivoting by columns for stability, and complete pivoting by rows for sparsity and by columns for stability. The factorization may optionally be modified to preserve the rowsums of the original matrix. The sparse matrix A is represented in coordinate storage (CS) format (see Section 2.1.1 of the F11 Chapter Introduction). The array A stores all the non-zero elements of the matrix A, while arrays IROW and ICOL store the corresponding row and column indices respectively. Multiple non-zero elements may not be specified for the same row and column index. The preconditioning matrix M is returned in terms of the CS representation of the matrix C 1⁄4 LþD 1 þ U 2I:
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