dlahqr man page on IRIX

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DLAHQR(3F)							    DLAHQR(3F)

NAME
     DLAHQR - i an auxiliary routine called by DHSEQR to update the
     eigenvalues and Schur decomposition already computed by DHSEQR, by
     dealing with the Hessenberg submatrix in rows and columns ILO to IHI

SYNOPSIS
     SUBROUTINE DLAHQR( WANTT, WANTZ, N, ILO, IHI, H, LDH, WR, WI, ILOZ, IHIZ,
			Z, LDZ, INFO )

	 LOGICAL	WANTT, WANTZ

	 INTEGER	IHI, IHIZ, ILO, ILOZ, INFO, LDH, LDZ, N

	 DOUBLE		PRECISION H( LDH, * ), WI( * ), WR( * ), Z( LDZ, * )

PURPOSE
     DLAHQR is an auxiliary routine called by DHSEQR to update the eigenvalues
     and Schur decomposition already computed by DHSEQR, by dealing with the
     Hessenberg submatrix in rows and columns ILO to IHI.

ARGUMENTS
     WANTT   (input) LOGICAL
	     = .TRUE. : the full Schur form T is required;
	     = .FALSE.: only eigenvalues are required.

     WANTZ   (input) LOGICAL
	     = .TRUE. : the matrix of Schur vectors Z is required;
	     = .FALSE.: Schur vectors are not required.

     N	     (input) INTEGER
	     The order of the matrix H.	 N >= 0.

     ILO     (input) INTEGER
	     IHI     (input) INTEGER It is assumed that H is already upper
	     quasi-triangular in rows and columns IHI+1:N, and that
	     H(ILO,ILO-1) = 0 (unless ILO = 1). DLAHQR works primarily with
	     the Hessenberg submatrix in rows and columns ILO to IHI, but
	     applies transformations to all of H if WANTT is .TRUE..  1 <= ILO
	     <= max(1,IHI); IHI <= N.

     H	     (input/output) DOUBLE PRECISION array, dimension (LDH,N)
	     On entry, the upper Hessenberg matrix H.  On exit, if WANTT is
	     .TRUE., H is upper quasi-triangular in rows and columns ILO:IHI,
	     with any 2-by-2 diagonal blocks in standard form. If WANTT is
	     .FALSE., the contents of H are unspecified on exit.

     LDH     (input) INTEGER
	     The leading dimension of the array H. LDH >= max(1,N).

									Page 1

DLAHQR(3F)							    DLAHQR(3F)

     WR	     (output) DOUBLE PRECISION array, dimension (N)
	     WI	     (output) DOUBLE PRECISION array, dimension (N) The real
	     and imaginary parts, respectively, of the computed eigenvalues
	     ILO to IHI are stored in the corresponding elements of WR and WI.
	     If two eigenvalues are computed as a complex conjugate pair, they
	     are stored in consecutive elements of WR and WI, say the i-th and
	     (i+1)th, with WI(i) > 0 and WI(i+1) < 0. If WANTT is .TRUE., the
	     eigenvalues are stored in the same order as on the diagonal of
	     the Schur form returned in H, with WR(i) = H(i,i), and, if
	     H(i:i+1,i:i+1) is a 2-by-2 diagonal block, WI(i) =
	     sqrt(H(i+1,i)*H(i,i+1)) and WI(i+1) = -WI(i).

     ILOZ    (input) INTEGER
	     IHIZ    (input) INTEGER Specify the rows of Z to which
	     transformations must be applied if WANTZ is .TRUE..  1 <= ILOZ <=
	     ILO; IHI <= IHIZ <= N.

     Z	     (input/output) DOUBLE PRECISION array, dimension (LDZ,N)
	     If WANTZ is .TRUE., on entry Z must contain the current matrix Z
	     of transformations accumulated by DHSEQR, and on exit Z has been
	     updated; transformations are applied only to the submatrix
	     Z(ILOZ:IHIZ,ILO:IHI).  If WANTZ is .FALSE., Z is not referenced.

     LDZ     (input) INTEGER
	     The leading dimension of the array Z. LDZ >= max(1,N).

     INFO    (output) INTEGER
	     = 0: successful exit
	     > 0: DLAHQR failed to compute all the eigenvalues ILO to IHI in a
	     total of 30*(IHI-ILO+1) iterations; if INFO = i, elements i+1:ihi
	     of WR and WI contain those eigenvalues which have been
	     successfully computed.

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