tevlc.f
SUBROUTINE TEVLC (N, D, E2, IERR)
C***BEGIN PROLOGUE TEVLC
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Warning: this routine is not intended to be user-callable.
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C***SUBSIDIARY
C***PURPOSE Subsidiary to CBLKTR
C***LIBRARY SLATEC
C***TYPE SINGLE PRECISION (TEVLC-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 CBLKTR
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 CCBLK
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 TEVLC