dpttrs(3)

NAME

DPTTRS - solve a tridiagonal system of the form A * X = B

using the L*D*L' factorization of A computed by DPTTRF

SYNOPSIS

SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
    INTEGER        INFO, LDB, N, NRHS
    DOUBLE         PRECISION B( LDB, * ), D( * ), E( * )

PURPOSE

DPTTRS solves a tridiagonal system of the form A * X = B

using the L*D*L' factorization of A computed by DPTTRF. D is a

diagonal matrix specified in the vector D, L is a unit bidiagonal

matrix whose subdiagonal is specified in the vector E, and X and

B are N by NRHS matrices.

ARGUMENTS

N (input) INTEGER

The order of the tridiagonal 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.

D (input) DOUBLE PRECISION array, dimension (N)

The n diagonal elements of the diagonal matrix D

from the L*D*L' factorization of A.

E (input) DOUBLE PRECISION array, dimension (N-1)

The (n-1) subdiagonal elements of the unit bidiag

onal factor L from the L*D*L' factorization of A. E can also be

regarded as the superdiagonal of the unit bidiagonal factor U

from the factorization A = U'*D*U.

B (input/output) DOUBLE PRECISION array, dimension

(LDB,NRHS)

On entry, the right hand side vectors B for the

system of linear equations. On exit, the solution vectors, X.

LDB (input) INTEGER

The leading dimension of the array B. LDB >=

max(1,N).

INFO (output) INTEGER

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

gal value

LAPACK version 3.0 15 June 2000

DPTTRS(3)