Compute an lu factorization of a complex tridiagonal matrix a using elimination without partial pivoting
SUBROUTINE SDTTRF(
N, DL, D, DU, INFO )
INTEGER
INFO, N
REAL
D( * ), DL( * ), DU( * )
SDTTRF 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.