FIGI2(3F)

NAME
     FIGI2, SFIGI2   -  EISPACK routine.  Given a NONSYMMETRIC TRIDIAGONAL
     matrix such that the products of corresponding pairs of off-diagonal
     elements are all non-negative, and zero only when both factors are zero,
     this subroutine reduces it to a SYMMETRIC TRIDIAGONAL matrix using and
     accumulating diagonal similarity transformations.


SYNOPSYS
          subroutine  figi2(nm, n, t, d, e, z, ierr)
          integer          nm, n, ierr
          double precision t(nm,3), d(n), e(n), z(nm,n)

          subroutine sfigi2(nm, n, t, d, e, z, ierr)
          integer          nm, n, ierr
          real             t(nm,3), d(n), e(n), z(nm,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.

     T contains the input 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.  On OUTPUT

     T is unaltered.

     D contains the diagonal elements of the symmetric matrix.

     E contains the subdiagonal elements of the symmetric matrix in its last
     N-1 positions.  E(1) is not set.

     Z contains the transformation matrix produced in the reduction.

     IERR is set to Zero       for normal return, N+I        if T(I,1)*T(I-
     1,3) is negative, 2*N+I      if T(I,1)*T(I-1,3) is zero with
        one factor non-zero.  Questions and comments should be directed to B.
     S. Garbow, APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL LABORATORY