DPTTRS(3) solves 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 bidiagonal 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 illegal value