DGTSV(3)                   MathKeisan LAPACK routine                  DGTSV(3)



NAME
       DGTSV - 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( * )

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) sub-diagonal elements of A.

               On  exit, DL is overwritten by the (n-2) elements of the second
               super-diagonal 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) super-diagonal elements of
               A.

               On exit, DU is overwritten by the (n-1) elements of  the  first
               super-diagonal of U.

       B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
               On entry, the N by NRHS matrix of 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.



 LAPACK routine (version 3.1)    November 2006                        DGTSV(3)