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DDTTRF - compute an LU factorization of a complex tridiagonal matrix A using elimination without partial pivoting

SUBROUTINE DDTTRF( N, DL, D, DU, INFO ) INTEGER INFO, N DOUBLE PRECISION D( * ), DL( * ), DU( * )

DDTTRF computes an LU factorization of a complex tridiagonal matrix A using elimination without partial pivoting. The factorization has the form A = L * U where L is a product of unit lower bidiagonal matrices and U is upper triangular with nonzeros in only the main diagonal and first superdiagonal.

N (input) INTEGER The order of the matrix A. N >= 0. DL (input/output) COMPLEX array, dimension (N-1) On entry, DL must contain the (n-1) subdiagonal elements of A. On exit, DL is overwritten by the (n-1) multipliers that define the matrix L from the LU factorization of A. D (input/output) COMPLEX array, dimension (N) On entry, D must contain the diagonal elements of A. On exit, D is overwritten by the n diagonal elements of the upper triangular matrix U from the LU factorization of A. DU (input/output) COMPLEX array, dimension (N-1) On entry, DU must contain the (n-1) superdiagonal elements of A. On exit, DU is overwritten by the (n-1) elements of the first superdiagonal of U. INFO (output) INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value > 0: if INFO = i, U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations.