SPTTRS(l) ) SPTTRS(l)NAME
SPTTRS - solve a tridiagonal system of the form A * X = B using the
L*D*L' factorization of A computed by SPTTRF
SYNOPSIS
SUBROUTINE SPTTRS( N, NRHS, D, E, B, LDB, INFO )
INTEGER INFO, LDB, N, NRHS
REAL B( LDB, * ), D( * ), E( * )
PURPOSE
SPTTRS solves a tridiagonal system of the form A * X = B using the
L*D*L' factorization of A computed by SPTTRF. D is a diagonal matrix
specified in the vector D, L is a unit bidiagonal matrix whose subdiag‐
onal 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) REAL array, dimension (N)
The n diagonal elements of the diagonal matrix D from the
L*D*L' factorization of A.
E (input) REAL 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 fac‐
torization A = U'*D*U.
B (input/output) REAL array, dimension (LDB,NRHS)
On entry, the right hand side vectors B for the system of lin‐
ear 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
LAPACK version 3.0 15 June 2000 SPTTRS(l)
