TINVIT(3F)

NAME
     TINVIT, STINVIT  -  EISPACK routine.  This subroutine finds those
     eigenvectors of a TRIDIAGONAL SYMMETRIC matrix corresponding to specified
     eigenvalues, using inverse iteration.


SYNOPSYS
          subroutine  tinvit(nm,n,d,e,e2,m,w,ind,z,ierr,rv1,rv2,rv3,rv4,rv6)
          integer           nm, n, m, ierr, ind(m)
          double precision d(n), e(n), e2(n), w(m), z(nm,m)
          double precision rv1(n), rv2(n), rv3(n), rv4(n), rv6(n)

          subroutine stinvit(nm,n,d,e,e2,m,w,ind,z,ierr,rv1,rv2,rv3,rv4,rv6)
          integer           nm, n, m, ierr, ind(m)
          real             d(n), e(n), e2(n), w(m), z(nm,m)
          real             rv1(n), rv2(n), rv3(n), rv4(n), rv6(n)



DESCRIPTION
     On Input

     NM must be set to the row dimension of two-dimensional array parameters
     as declared in the calling program dimension statement.

     N is the order of the matrix.

     D contains the diagonal elements of the input matrix.

     E contains the subdiagonal elements of the input matrix in its last N-1
     positions.  E(1) is arbitrary.

     E2 contains the squares of the corresponding elements of E, with zeros
     corresponding to negligible elements of E.  E(I) is considered negligible
     if it is not larger than the product of the relative machine precision
     and the sum of the magnitudes of D(I) and D(I-1).  E2(1) must contain
     0.0e0 if the eigenvalues are in ascending order, or 2.0e0 if the
     eigenvalues are in descending order.  If  BISECT, TRIDIB, or  IMTQLV  has
     been used to find the eigenvalues, their output E2 array is exactly what
     is expected here.

     M is the number of specified eigenvalues.

     W CONTAINS the M eigenvalues in ascending or descending order.

     IND contains in its first M positions the submatrix indices associated
     with the corresponding eigenvalues in W -- 1 for eigenvalues belonging to
     the first submatrix from the top, 2 for those belonging to the second
     submatrix, etc.  On Output

     Z contains the associated set of orthonormal eigenvectors. any vector
     which fails to converge is set to zero.
     IERR is set to Zero       for normal return, -R         if the
     eigenvector corresponding to the R-th
        eigenvalue fails to converge in 5 iterations.

     RV1 , RV2, RV3, RV4, and RV6 are temporary storage arrays. Questions and
     comments should be directed to B. S. Garbow, APPLIED MATHEMATICS
     DIVISION, ARGONNE NATIONAL LABORATORY