!-----------------------------------------------------------------
!
! Purpose
! =======
!
!  LA_STEVD computes all eigenvalues and, optionally, eigenvectors of
!  a real symmetric tridiagonal matrix. If eigenvectors are desired,
!  it uses a divide and conquer algorithm.
!
!  The divide and conquer algorithm makes very mild assumptions about
!  floating point arithmetic. It will work on machines with a guard
!  digit in add/subtract, or on those binary machines without guard
!  digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
!  Cray-2. It could conceivably fail on hexadecimal or decimal machines
!  without guard digits, but we know of none.
!
!  Arguments
!  =========
!
!  SUBROUTINE LA_STEV( D, E, Z, INFO )
!     REAL(<wp>), INTENT(INOUT) :: D(:), E(:)
!     REAL(<wp>), INTENT(OUT), OPTIONAL :: Z(:,:)
!     INTEGER, INTENT(OUT), OPTIONAL :: INFO
!  where
!     <wp>   ::= KIND(1.0) | KIND(1.0D0)
!
! Arguments
! =========
!
! D    (input/output) REAL array shape (:), where SIZE(D)
!      indicates the matrix rank (n)
!      On entry, the n diagonal elements of the tridiagonal matrix
!      A.
!      On exit, if INFO = 0, the eigenvalues in ascending order.
!
! E    (input/output) REAL array, shape (:), where
!      SIZE(E) == SIZE(D).
!      On entry, the (n-1) subdiagonal elements of the tridiagonal
!      matrix A, stored in elements 1 to n-1 of E; E(n) need not
!      be set, but is used by the routine.
!      On exit, the contents of E are destroyed.
!
! Z    (output) REAL array, shape(:,:), SIZE(Z,1) == SIZE(Z,2) == n.
!      If INFO = 0, Z contains the orthonormal eigenvectors of the
!      matrix A, with the i-th column of Z holding the eigenvector
!      associated with D(i).
!
! INFO (output) INTEGER
!      = 0:  successful exit
!      < 0:  if INFO = -i, the i-th argument had an illegal value
!      > 0:  if INFO = i, the algorithm failed to converge; i
!            off-diagonal elements of E did not converge to zero.
!      If INFO is not present and an error occurs, then the program
!      is terminated with an error message.
!-------------------------------------

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