CDTTRF ‐ compute an LU factorization of a complex tridiagonal ma‐
trix A using elimination without partial pivoting SUBROUTINE CDT‐
TRF( N, DL, D, DU, INFO )
INTEGER INFO, N
COMPLEX D( * ), DL( * ), DU( * ) CDTTRF computes an LU fac‐
torization of a complex tridiagonal matrix A using eliminationwithout partial pivoting. The factorization has the form
A = L * U
where L is a product of unit lower bidiagonalmatrices and U is upper triangular with nonzeros in only the maindiagonal 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 ele‐
ments 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 superdiago‐
nal 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 divi‐
sion by zero will occur if it is used to solve a system of equa‐
tions.
