_HTRIDI(3F)_HTRIDI(3F)NAME
HTRIDI, SHTRIDI - EISPACK routine. This subroutine reduces a COMPLEX
HERMITIAN matrix to a real symmetric tridiagonal matrix using unitary
similarity transformations.
SYNOPSYS
subroutine htridi(nm, n, ar, ai, d, e, e2, tau)
integer nm, n
double precision ar(nm,n),ai(nm,n),d(n),e(n),e2(n),tau(2,n)
subroutine shtridi(nm, n, ar, ai, d, e, e2, tau)
integer nm, n
real ar(nm,n),ai(nm,n),d(n),e(n),e2(n),tau(2,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.
AR and AI contain the real and imaginary parts, respectively, of the
complex hermitian input matrix. Only the lower triangle of the matrix
need be supplied. On OUTPUT
AR and AI contain information about the unitary trans- formations used in
the reduction in their full lower triangles. Their strict upper
triangles and the diagonal of AR are unaltered.
D contains the diagonal elements of the tridiagonal matrix.
E contains the subdiagonal elements of the tridiagonal matrix in its last
N-1 positions. E(1) is set to zero.
E2 contains the squares of the corresponding elements of E. E2 may
coincide with E if the squares are not needed.
TAU contains further information about the transformations. Calls
PYTHAG(A,B) for sqrt(A**2 + B**2). Questions and comments should be
directed to B. S. Garbow, APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL
LABORATORY
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