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SLAHQR(3F)							    SLAHQR(3F)


NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SLAHQR(	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

	 REAL		H( LDH,	* ), WI( * ), WR( * ), Z( LDZ, * )

PURPOSE    [Toc]    [Back]

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

ARGUMENTS    [Toc]    [Back]

     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).	SLAHQR 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) REAL 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






SLAHQR(3F)							    SLAHQR(3F)



     WR	     (output) REAL array, dimension (N)
	     WI	     (output) REAL 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) REAL array,	dimension (LDZ,N)
	     If	WANTZ is .TRUE., on entry Z must contain the current matrix Z
	     of	transformations	accumulated by SHSEQR, 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: SLAHQR 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.
SLAHQR(3F)							    SLAHQR(3F)


NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SLAHQR(	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

	 REAL		H( LDH,	* ), WI( * ), WR( * ), Z( LDZ, * )

PURPOSE    [Toc]    [Back]

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

ARGUMENTS    [Toc]    [Back]

     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).	SLAHQR 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) REAL 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






SLAHQR(3F)							    SLAHQR(3F)



     WR	     (output) REAL array, dimension (N)
	     WI	     (output) REAL 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) REAL array,	dimension (LDZ,N)
	     If	WANTZ is .TRUE., on entry Z must contain the current matrix Z
	     of	transformations	accumulated by SHSEQR, 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: SLAHQR 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.


									PPPPaaaaggggeeee 2222
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