!-----------------------------------------------------------------
!
!  Purpose
!  =======
!
!  LA_GTSV  solves the equation A*X = B, where A is a 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
!  =========
!
!   SUBROUTINE LA_GTSV( DL, D, DU, B, INFO )
!       <type>(<wp>), INTENT(INOUT) :: DL(:), D(:), DU(:), <rhs>
!       INTEGER, INTENT(OUT), OPTIONAL :: INFO
!     <type> ::= REAL | COMPLEX
!     <wp>   ::= KIND(1.0) | KIND(1.0D0)
!     <rhs>  ::= B(:,:) | B(:)
!
!  =====================
!
!  DL      (input/output) either REAL or COMPLEX array, shape (:), where
!          SIZE(DL) == SIZE(D) -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) either REAL or COMPLEX array, shape (:), where
!          SIZE(D) indicates the matrix rank (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) either REAL or COMPLEX array, shape (:), where
!          SIZE(DL) == SIZE(D) -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) either REAL or COMPLEX rectangular array,
!       shape either (:,:) or (:), size(B,1) or size(B) == size(D).
!       On entry, the right hand side vector(s) of matrix B for the
!          system of equations AX = B.
!       On exit, if there is no error, the matrix of solution
!          vector(s) X.
!
!  INFO Optional (output) INTEGER.
!       If INFO is present
!          = 0: successful exit
!          < 0: if INFO = -k, the k-th argument had an illegal value
!          > 0: if INFO = k, U(k,k) is exactly zero.  The factorization
!               has been completed, but the factor U is exactly
!               singular, so the solution could not be computed.
!       If INFO is not present and an error occurs, then the program is
!          terminated with an error message.
!
!-------------------------------------

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