NAME

dgttrs - solve one of the systems of equations  A∗X = B or A’∗X = B,

SYNOPSIS

SUBROUTINE DGTTRS(
TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB, INFO )

CHARACTER TRANS

INTEGER INFO, LDB, N, NRHS

INTEGER IPIV( ∗ )

DOUBLE PRECISION B( LDB, ∗ ), D( ∗ ), DL( ∗ ), DU( ∗ ), DU2( ∗ )

PURPOSE

DGTTRS solves one of the systems of equations
   A∗X = B  or  A’∗X = B, with a tridiagonal matrix A using the LU factorization computed by DGTTRF.
 

ARGUMENTS

TRANS   (input) CHARACTER
Specifies the form of the system of equations:
= ’N’:  A ∗ X = B  (No transpose)
= ’T’:  A’∗ X = B  (Transpose)
= ’C’:  A’∗ X = B  (Conjugate transpose = Transpose)

N       (input) INTEGER
The order of the 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.

DL      (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) multipliers that define the matrix L from the LU factorization of A.

D       (input) DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the upper triangular matrix U from the LU factorization of A.

DU      (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) elements of the first superdiagonal of U.

DU2     (input) DOUBLE PRECISION array, dimension (N-2)
The (n-2) elements of the second superdiagonal of U.

IPIV    (input) INTEGER array, dimension (N)
The pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i).  IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required.

B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
On entry, the right hand side matrix B. On exit, B is overwritten by the solution matrix X.

LDB     (input) INTEGER
The leading dimension of the array B.  LDB >= max(1,N).

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

SunSoft, Inc.  —  Last change: 27 Jun 1995