SYNOPSIS

SUBROUTINE DDTTRF(

N, DL, D, DU, INFO )

    

INTEGER INFO, N

    

DOUBLE PRECISION D( * ), DL( * ), DU( * )

PURPOSE

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.

ARGUMENTS

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.