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man pages->IRIX man pages -> complib/HTRIDI (3)
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### Contents

_HTRIDI(3F)							   _HTRIDI(3F)

### NAME[Toc][Back]

HTRIDI, SHTRIDI  -	 EISPACK routine.  This	subroutine reduces a COMPLEX
HERMITIAN matrix to a real	symmetric tridiagonal matrix using unitary
similarity	transformations.

### SYNOPSYS[Toc][Back]

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[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.

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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