NAME

dgtsv - solve the equation   A∗X = B,

SYNOPSIS

SUBROUTINE DGTSV( N, NRHS, DL, D, DU, B, LDB, INFO )

INTEGER INFO, LDB, N, NRHS

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

#include <sunperf.h>

void dgtsv(int n, int nrhs, double ∗dl, double ∗d, double ∗du, double ∗db, int ldb, int ∗info) ;

PURPOSE

DGTSV  solves the equation
 
where A is an N-by-N tridiagonal matrix, by Gaussian elimination with partial pivoting.
 
Note that the equation  A’∗X = B  may be solved by interchanging the order of the arguments DU and DL.
 

ARGUMENTS

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/output) DOUBLE PRECISION array, dimension (N-1)
On entry, DL must contain the (n-1) subdiagonal elements of A. On exit, DL is overwritten by the (n-2) elements of the second superdiagonal of the upper triangular matrix U from the LU factorization of A, in DL(1), ..., DL(n-2).

D (input/output) DOUBLE PRECISION array, dimension (N)
On entry, D must contain the diagonal elements of A. On exit, D is overwritten by the n diagonal elements of U.

DU (input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, DU must contain the (n-1) superdiagonal elements of A. On exit, DU is overwritten by the (n-1) elements of the first superdiagonal of U.

B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
On entry, the N-by-NRHS right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS 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
> 0:  if INFO = i, U(i,i) is exactly zero, and the solution has not been computed.  The factorization has not been completed unless i = N.

SunOS 5.0  —  Last change: 10 Dec 1998