DSTERF computes all eigenvalues of a symmetric tridiagonal matrix
 using the Pal-Walker-Kahan variant of the QL or QR algorithm.

          N is INTEGER
          The order of the matrix.  N >= 0.

          D is DOUBLE PRECISION array, dimension (N)
          On entry, the n diagonal elements of the tridiagonal matrix.
          On exit, if INFO = 0, the eigenvalues in ascending order.

          E is DOUBLE PRECISION array, dimension (N-1)
          On entry, the (n-1) subdiagonal elements of the tridiagonal
          matrix.
          On exit, E has been destroyed.

          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  the algorithm failed to find all of the eigenvalues in
                a total of 30*N iterations; if INFO = i, then i
                elements of E have not converged to zero.