_FIGI2(3F)							    _FIGI2(3F)

NAME    [Toc]    [Back]

     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    [Toc]    [Back]

	  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    [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 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(I1,3)
 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


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