_BAKVEC(3F)							   _BAKVEC(3F)

NAME    [Toc]    [Back]

     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    [Toc]    [Back]

	  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    [Toc]    [Back]

     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


									PPPPaaaaggggeeee 1111