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 (N1)
 On entry, DL must contain the (n1) subdiagonal elements of A. On exit, DL is overwritten by the (n2) elements of the second superdiagonal of the upper triangular matrix U from the LU factorization of A, in DL(1), ..., DL(n2).
 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 (N1)
 On entry, DU must contain the (n1) superdiagonal elements of A. On exit, DU is overwritten by the (n1) elements of the first superdiagonal 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 ith 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.