SLATEC Routines --- TEVLS ---

*DECK TEVLS
      SUBROUTINE TEVLS (N, D, E2, IERR)
C***BEGIN PROLOGUE  TEVLS
C***SUBSIDIARY
C***PURPOSE  Subsidiary to BLKTRI
C***LIBRARY   SLATEC
C***TYPE      SINGLE PRECISION (TEVLS-S)
C***AUTHOR  (UNKNOWN)
C***DESCRIPTION
C
C     This subroutine finds the eigenvalues of a symmetric tridiagonal
C     matrix by the rational QL method.
C
C     On Input-
C
C        N is the order of the matrix,
C
C        D contains the diagonal elements of the input matrix,
C
C        E2 contains the subdiagonal elements of the input matrix
C           in its last N-1 positions.  E2(1) is arbitrary.
C
C      On Output-
C
C        D contains the eigenvalues in ascending order.  If an
C          error exit is made, the eigenvalues are correct and
C          ordered for indices 1,2,...IERR-1, but may not be
C          the smallest eigenvalues,
C
C        E2 has been destroyed,
C
C        IERR is set to
C          ZERO       for normal return,
C          J          if the J-th eigenvalue has not been
C                     determined after 30 iterations.
C
C***SEE ALSO  BLKTRI
C***REFERENCES  C. H. Reinsch, Eigenvalues of a real, symmetric, tri-
C                 diagonal matrix, Algorithm 464, Communications of the
C                 ACM 16, 11 (November 1973), pp. 689.
C***ROUTINES CALLED  (NONE)
C***COMMON BLOCKS    CBLKT
C***REVISION HISTORY  (YYMMDD)
C   801001  DATE WRITTEN
C   890831  Modified array declarations.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900402  Added TYPE section.  (WRB)
C   920528  DESCRIPTION revised and REFERENCES section added.  (WRB)
C***END PROLOGUE  TEVLS