cpttrs(3)

NAME

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

using the factorization A = U'*D*U or A = L*D*L' computed by CPT

TRF

SYNOPSIS

SUBROUTINE CPTTRS( UPLO, N, NRHS, D, E, B, LDB, INFO )
    CHARACTER      UPLO
    INTEGER        INFO, LDB, N, NRHS
    REAL           D( * )
    COMPLEX        B( LDB, * ), E( * )

PURPOSE

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

using the factorization A = U'*D*U or A = L*D*L' computed by CPT

TRF. D is a diagonal matrix specified in the vector D, U (or L)

is a unit bidiagonal matrix whose superdiagonal (subdiagonal) is

specified in the vector E, and X and B are N by NRHS matrices.

ARGUMENTS

UPLO (input) CHARACTER*1

Specifies the form of the factorization and

whether the vector E is the superdiagonal of the upper bidiagonal

factor U or the subdiagonal of the lower bidiagonal factor L. =

'U': A = U'*D*U, E is the superdiagonal of U
= 'L': A = L*D*L', E is the subdiagonal of L

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) REAL array, dimension (N)

The n diagonal elements of the diagonal matrix D

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

E (input) COMPLEX array, dimension (N-1)

If UPLO = 'U', the (n-1) superdiagonal elements of

the unit bidiagonal factor U from the factorization A = U'*D*U.

If UPLO = 'L', the (n-1) subdiagonal elements of the unit bidiag

onal factor L from the factorization A = L*D*L'.

B (input/output) REAL 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

CPTTRS(3)