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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  elimi-
     nation with partial pivoting.

     Note that the equation  A'*X = B  may be  solved  by  inter-
     changing 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 factoriza-
               tion 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 ille-
               gal 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.

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