cgtsv(3)

NAME

CGTSV - solve the equation A*X = B,

SYNOPSIS

SUBROUTINE CGTSV( N, NRHS, DL, D, DU, B, LDB, INFO )
    INTEGER       INFO, LDB, N, NRHS
    COMPLEX       B( LDB, * ), D( * ), DL( * ), DU( * )

PURPOSE

CGTSV solves the equation A*X = B, where A is an N-by-N

tridiagonal matrix, by Gaussian elimination with partial pivot

ing.

Note that the equation A'*X = B may be solved by inter

changing the order of the arguments DU and DL.

ARGUMENTS

N (input) INTEGER

The order of the matrix A. N >= 0.

NRHS (input) INTEGER

The number of right hand sides, i.e., the number

of columns of the matrix B. NRHS >= 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-2) elements

of the second superdiagonal of the upper triangular matrix U from

the LU factorization of A, in DL(1), ..., DL(n-2).

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 U.

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.

B (input/output) COMPLEX array, dimension (LDB,NRHS)

On entry, the N-by-NRHS right hand side matrix B.

On exit, if INFO = 0, the N-by-NRHS solution matrix X.

LDB (input) INTEGER

The leading dimension of the array B. LDB >=

max(1,N).

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value
> 0: if INFO = i, U(i,i) is exactly zero, and the

solution has not been computed. The factorization has not been

completed unless i = N.

LAPACK version 3.0 15 June 2000

CGTSV(3)