BAKVEC(3F)

NAME
     BAKVEC, SBAKVEC  -  EISPACK routine.  This subroutine forms the
     eigenvectors of a NONSYMMETRIC TRIDIAGONAL matrix by back transforming
     those of the corresponding symmetric matrix determined by  FIGI.


SYNOPSYS
          subroutine bakvec(nm, n, t, e, m, z, ierr)
          integer          m, n, nm, ierr
          double precision t(nm,3), e(n), z(nm,m)

          subroutine sbakvec(nm, n, t, e, m, z, ierr)
          integer          m, n, nm, ierr
          real             t(nm,3), e(n), z(nm, m)



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.

     T contains the nonsymmetric matrix.  Its subdiagonal is stored in the
     last N-1 positions of the first column, its diagonal in the N positions
     of the second column, and its superdiagonal in the first N-1 positions of
     the third column.  T(1,1) and T(N,3) are arbitrary.

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

     M is the number of eigenvectors to be back transformed.

     Z contains the eigenvectors to be back transformed in its first M
     columns.  On OUTPUT

     T is unaltered.

     E is  Destroyed.

     Z contains the transformed eigenvectors in its first M columns.

     IERR is set to Zero       for normal return, 2*N+I      if E(I) is zero
     with T(I,1) or T(I-1,3) non-zero.
        In this case, the symmetric matrix is not similar
        to the original matrix, and the eigenvectors
        cannot be found by this program.  Questions and comments should be
     directed to B. S. Garbow, APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL
     LABORATORY