_FIGI2(3F)_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
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