!-----------------------------------------------------------------
!
! Purpose
! =======
!
! LA_PTSV computes the solution to a system of linear equations
! A*X = B, where A is either a symmetric positive definite or
! hermitia tridiagonal matrix, and X and B are either retriangular
! matrices or vectors.
! A is factored as A = L*D*L**T, and the factored form of A is then
! used to solve the system of equations.
!
! Arguments
! =========
!
!  SUBROUTINE LA_PTSV( D, E, B, INFO )
!    REAL(<wp>), INTENT(INOUT) :: D(:)
!    <type>(<wp>), INTENT(INOUT) :: E(:), <rhs>
!    INTEGER, INTENT(OUT), OPTIONAL :: INFO
!    <type> ::= REAL | COMPLEX
!    <wp>   ::= KIND(1.0) | KIND(1.0D0)
!    <rhs>  ::= B(:,:) | B(:)
!
! =====================
!
! D    (input/output) either REAL array, shape (:), where SIZE(D)
!      indicates the matrix rank (n).
!      On entry, the n diagonal elements of the tridiagonal matrix
!      A.  On exit, the n diagonal elements of the diagonal matrix
!      D from the factorization A = L*D*L**T.
!
! E    (input/output) either REAL or COMPLEX array, shape (:), where
!      SIZE(E) == SIZE(D)-1.
!      On entry, the (n-1) subdiagonal elements of the tridiagonal
!      matrix A.  On exit, the (n-1) subdiagonal elements of the
!      unit bidiagonal factor L from the L*D*L**T factorization of
!      A.  (E can also be regarded as the superdiagonal of the unit
!      bidiagonal factor U from the U**T*D*U factorization of A.)
!
! 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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