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 CPTTRF. 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 bidiagonal 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 illegal value