lib
/
LAPACK-3.11.0
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
Cloned library LAPACK-3.11.0 with extra build files for internal package management.
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
3 Commits
1 Branch
0 Tags
5.8 MiB
Tag: Branch: Tree: main
Branches Tags
${ item.name }
Create tag ${ searchTerm }
Create branch ${ searchTerm }
from 'main'
${ noResults }
LAPACK-3.11.0/SRC/stgsen.f

863 lines
29 KiB
Raw Permalink Normal View History Unescape

Initial commit
2 years ago
*> \brief \b STGSEN
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download STGSEN + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/stgsen.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/stgsen.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/stgsen.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* SUBROUTINE STGSEN( IJOB, WANTQ, WANTZ, SELECT, N, A, LDA, B, LDB,
* ALPHAR, ALPHAI, BETA, Q, LDQ, Z, LDZ, M, PL,
* PR, DIF, WORK, LWORK, IWORK, LIWORK, INFO )
*
* .. Scalar Arguments ..
* LOGICAL WANTQ, WANTZ
* INTEGER IJOB, INFO, LDA, LDB, LDQ, LDZ, LIWORK, LWORK,
* $ M, N
* REAL PL, PR
* ..
* .. Array Arguments ..
* LOGICAL SELECT( * )
* INTEGER IWORK( * )
* REAL A( LDA, * ), ALPHAI( * ), ALPHAR( * ),
* $ B( LDB, * ), BETA( * ), DIF( * ), Q( LDQ, * ),
* $ WORK( * ), Z( LDZ, * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> STGSEN reorders the generalized real Schur decomposition of a real
*> matrix pair (A, B) (in terms of an orthonormal equivalence trans-
*> formation Q**T * (A, B) * Z), so that a selected cluster of eigenvalues
*> appears in the leading diagonal blocks of the upper quasi-triangular
*> matrix A and the upper triangular B. The leading columns of Q and
*> Z form orthonormal bases of the corresponding left and right eigen-
*> spaces (deflating subspaces). (A, B) must be in generalized real
*> Schur canonical form (as returned by SGGES), i.e. A is block upper
*> triangular with 1-by-1 and 2-by-2 diagonal blocks. B is upper
*> triangular.
*>
*> STGSEN also computes the generalized eigenvalues
*>
*> w(j) = (ALPHAR(j) + i*ALPHAI(j))/BETA(j)
*>
*> of the reordered matrix pair (A, B).
*>
*> Optionally, STGSEN computes the estimates of reciprocal condition
*> numbers for eigenvalues and eigenspaces. These are Difu[(A11,B11),
*> (A22,B22)] and Difl[(A11,B11), (A22,B22)], i.e. the separation(s)
*> between the matrix pairs (A11, B11) and (A22,B22) that correspond to
*> the selected cluster and the eigenvalues outside the cluster, resp.,
*> and norms of "projections" onto left and right eigenspaces w.r.t.
*> the selected cluster in the (1,1)-block.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] IJOB
*> \verbatim
*> IJOB is INTEGER
*> Specifies whether condition numbers are required for the
*> cluster of eigenvalues (PL and PR) or the deflating subspaces
*> (Difu and Difl):
*> =0: Only reorder w.r.t. SELECT. No extras.
*> =1: Reciprocal of norms of "projections" onto left and right
*> eigenspaces w.r.t. the selected cluster (PL and PR).
*> =2: Upper bounds on Difu and Difl. F-norm-based estimate
*> (DIF(1:2)).
*> =3: Estimate of Difu and Difl. 1-norm-based estimate
*> (DIF(1:2)).
*> About 5 times as expensive as IJOB = 2.
*> =4: Compute PL, PR and DIF (i.e. 0, 1 and 2 above): Economic
*> version to get it all.
*> =5: Compute PL, PR and DIF (i.e. 0, 1 and 3 above)
*> \endverbatim
*>
*> \param[in] WANTQ
*> \verbatim
*> WANTQ is LOGICAL
*> .TRUE. : update the left transformation matrix Q;
*> .FALSE.: do not update Q.
*> \endverbatim
*>
*> \param[in] WANTZ
*> \verbatim
*> WANTZ is LOGICAL
*> .TRUE. : update the right transformation matrix Z;
*> .FALSE.: do not update Z.
*> \endverbatim
*>
*> \param[in] SELECT
*> \verbatim
*> SELECT is LOGICAL array, dimension (N)
*> SELECT specifies the eigenvalues in the selected cluster.
*> To select a real eigenvalue w(j), SELECT(j) must be set to
*> .TRUE.. To select a complex conjugate pair of eigenvalues
*> w(j) and w(j+1), corresponding to a 2-by-2 diagonal block,
*> either SELECT(j) or SELECT(j+1) or both must be set to
*> .TRUE.; a complex conjugate pair of eigenvalues must be
*> either both included in the cluster or both excluded.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The order of the matrices A and B. N >= 0.
*> \endverbatim
*>
*> \param[in,out] A
*> \verbatim
*> A is REAL array, dimension(LDA,N)
*> On entry, the upper quasi-triangular matrix A, with (A, B) in
*> generalized real Schur canonical form.
*> On exit, A is overwritten by the reordered matrix A.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*> LDA is INTEGER
*> The leading dimension of the array A. LDA >= max(1,N).
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*> B is REAL array, dimension(LDB,N)
*> On entry, the upper triangular matrix B, with (A, B) in
*> generalized real Schur canonical form.
*> On exit, B is overwritten by the reordered matrix B.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*> LDB is INTEGER
*> The leading dimension of the array B. LDB >= max(1,N).
*> \endverbatim
*>
*> \param[out] ALPHAR
*> \verbatim
*> ALPHAR is REAL array, dimension (N)
*> \endverbatim
*>
*> \param[out] ALPHAI
*> \verbatim
*> ALPHAI is REAL array, dimension (N)
*> \endverbatim
*>
*> \param[out] BETA
*> \verbatim
*> BETA is REAL array, dimension (N)
*>
*> On exit, (ALPHAR(j) + ALPHAI(j)*i)/BETA(j), j=1,...,N, will
*> be the generalized eigenvalues. ALPHAR(j) + ALPHAI(j)*i
*> and BETA(j),j=1,...,N are the diagonals of the complex Schur
*> form (S,T) that would result if the 2-by-2 diagonal blocks of
*> the real generalized Schur form of (A,B) were further reduced
*> to triangular form using complex unitary transformations.
*> If ALPHAI(j) is zero, then the j-th eigenvalue is real; if
*> positive, then the j-th and (j+1)-st eigenvalues are a
*> complex conjugate pair, with ALPHAI(j+1) negative.
*> \endverbatim
*>
*> \param[in,out] Q
*> \verbatim
*> Q is REAL array, dimension (LDQ,N)
*> On entry, if WANTQ = .TRUE., Q is an N-by-N matrix.
*> On exit, Q has been postmultiplied by the left orthogonal
*> transformation matrix which reorder (A, B); The leading M
*> columns of Q form orthonormal bases for the specified pair of
*> left eigenspaces (deflating subspaces).
*> If WANTQ = .FALSE., Q is not referenced.
*> \endverbatim
*>
*> \param[in] LDQ
*> \verbatim
*> LDQ is INTEGER
*> The leading dimension of the array Q. LDQ >= 1;
*> and if WANTQ = .TRUE., LDQ >= N.
*> \endverbatim
*>
*> \param[in,out] Z
*> \verbatim
*> Z is REAL array, dimension (LDZ,N)
*> On entry, if WANTZ = .TRUE., Z is an N-by-N matrix.
*> On exit, Z has been postmultiplied by the left orthogonal
*> transformation matrix which reorder (A, B); The leading M
*> columns of Z form orthonormal bases for the specified pair of
*> left eigenspaces (deflating subspaces).
*> If WANTZ = .FALSE., Z is not referenced.
*> \endverbatim
*>
*> \param[in] LDZ
*> \verbatim
*> LDZ is INTEGER
*> The leading dimension of the array Z. LDZ >= 1;
*> If WANTZ = .TRUE., LDZ >= N.
*> \endverbatim
*>
*> \param[out] M
*> \verbatim
*> M is INTEGER
*> The dimension of the specified pair of left and right eigen-
*> spaces (deflating subspaces). 0 <= M <= N.
*> \endverbatim
*>
*> \param[out] PL
*> \verbatim
*> PL is REAL
*> \endverbatim
*>
*> \param[out] PR
*> \verbatim
*> PR is REAL
*>
*> If IJOB = 1, 4 or 5, PL, PR are lower bounds on the
*> reciprocal of the norm of "projections" onto left and right
*> eigenspaces with respect to the selected cluster.
*> 0 < PL, PR <= 1.
*> If M = 0 or M = N, PL = PR = 1.
*> If IJOB = 0, 2 or 3, PL and PR are not referenced.
*> \endverbatim
*>
*> \param[out] DIF
*> \verbatim
*> DIF is REAL array, dimension (2).
*> If IJOB >= 2, DIF(1:2) store the estimates of Difu and Difl.
*> If IJOB = 2 or 4, DIF(1:2) are F-norm-based upper bounds on
*> Difu and Difl. If IJOB = 3 or 5, DIF(1:2) are 1-norm-based
*> estimates of Difu and Difl.
*> If M = 0 or N, DIF(1:2) = F-norm([A, B]).
*> If IJOB = 0 or 1, DIF is not referenced.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*> WORK is REAL array, dimension (MAX(1,LWORK))
*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*> \endverbatim
*>
*> \param[in] LWORK
*> \verbatim
*> LWORK is INTEGER
*> The dimension of the array WORK. LWORK >= 4*N+16.
*> If IJOB = 1, 2 or 4, LWORK >= MAX(4*N+16, 2*M*(N-M)).
*> If IJOB = 3 or 5, LWORK >= MAX(4*N+16, 4*M*(N-M)).
*>
*> If LWORK = -1, then a workspace query is assumed; the routine
*> only calculates the optimal size of the WORK array, returns
*> this value as the first entry of the WORK array, and no error
*> message related to LWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] IWORK
*> \verbatim
*> IWORK is INTEGER array, dimension (MAX(1,LIWORK))
*> On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
*> \endverbatim
*>
*> \param[in] LIWORK
*> \verbatim
*> LIWORK is INTEGER
*> The dimension of the array IWORK. LIWORK >= 1.
*> If IJOB = 1, 2 or 4, LIWORK >= N+6.
*> If IJOB = 3 or 5, LIWORK >= MAX(2*M*(N-M), N+6).
*>
*> If LIWORK = -1, then a workspace query is assumed; the
*> routine only calculates the optimal size of the IWORK array,
*> returns this value as the first entry of the IWORK array, and
*> no error message related to LIWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*> INFO is INTEGER
*> =0: Successful exit.
*> <0: If INFO = -i, the i-th argument had an illegal value.
*> =1: Reordering of (A, B) failed because the transformed
*> matrix pair (A, B) would be too far from generalized
*> Schur form; the problem is very ill-conditioned.
*> (A, B) may have been partially reordered.
*> If requested, 0 is returned in DIF(*), PL and PR.
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup realOTHERcomputational
*
*> \par Further Details:
* =====================
*>
*> \verbatim
*>
*> STGSEN first collects the selected eigenvalues by computing
*> orthogonal U and W that move them to the top left corner of (A, B).
*> In other words, the selected eigenvalues are the eigenvalues of
*> (A11, B11) in:
*>
*> U**T*(A, B)*W = (A11 A12) (B11 B12) n1
*> ( 0 A22),( 0 B22) n2
*> n1 n2 n1 n2
*>
*> where N = n1+n2 and U**T means the transpose of U. The first n1 columns
*> of U and W span the specified pair of left and right eigenspaces
*> (deflating subspaces) of (A, B).
*>
*> If (A, B) has been obtained from the generalized real Schur
*> decomposition of a matrix pair (C, D) = Q*(A, B)*Z**T, then the
*> reordered generalized real Schur form of (C, D) is given by
*>
*> (C, D) = (Q*U)*(U**T*(A, B)*W)*(Z*W)**T,
*>
*> and the first n1 columns of Q*U and Z*W span the corresponding
*> deflating subspaces of (C, D) (Q and Z store Q*U and Z*W, resp.).
*>
*> Note that if the selected eigenvalue is sufficiently ill-conditioned,
*> then its value may differ significantly from its value before
*> reordering.
*>
*> The reciprocal condition numbers of the left and right eigenspaces
*> spanned by the first n1 columns of U and W (or Q*U and Z*W) may
*> be returned in DIF(1:2), corresponding to Difu and Difl, resp.
*>
*> The Difu and Difl are defined as:
*>
*> Difu[(A11, B11), (A22, B22)] = sigma-min( Zu )
*> and
*> Difl[(A11, B11), (A22, B22)] = Difu[(A22, B22), (A11, B11)],
*>
*> where sigma-min(Zu) is the smallest singular value of the
*> (2*n1*n2)-by-(2*n1*n2) matrix
*>
*> Zu = [ kron(In2, A11) -kron(A22**T, In1) ]
*> [ kron(In2, B11) -kron(B22**T, In1) ].
*>
*> Here, Inx is the identity matrix of size nx and A22**T is the
*> transpose of A22. kron(X, Y) is the Kronecker product between
*> the matrices X and Y.
*>
*> When DIF(2) is small, small changes in (A, B) can cause large changes
*> in the deflating subspace. An approximate (asymptotic) bound on the
*> maximum angular error in the computed deflating subspaces is
*>
*> EPS * norm((A, B)) / DIF(2),
*>
*> where EPS is the machine precision.
*>
*> The reciprocal norm of the projectors on the left and right
*> eigenspaces associated with (A11, B11) may be returned in PL and PR.
*> They are computed as follows. First we compute L and R so that
*> P*(A, B)*Q is block diagonal, where
*>
*> P = ( I -L ) n1 Q = ( I R ) n1
*> ( 0 I ) n2 and ( 0 I ) n2
*> n1 n2 n1 n2
*>
*> and (L, R) is the solution to the generalized Sylvester equation
*>
*> A11*R - L*A22 = -A12
*> B11*R - L*B22 = -B12
*>
*> Then PL = (F-norm(L)**2+1)**(-1/2) and PR = (F-norm(R)**2+1)**(-1/2).
*> An approximate (asymptotic) bound on the average absolute error of
*> the selected eigenvalues is
*>
*> EPS * norm((A, B)) / PL.
*>
*> There are also global error bounds which valid for perturbations up
*> to a certain restriction: A lower bound (x) on the smallest
*> F-norm(E,F) for which an eigenvalue of (A11, B11) may move and
*> coalesce with an eigenvalue of (A22, B22) under perturbation (E,F),
*> (i.e. (A + E, B + F), is
*>
*> x = min(Difu,Difl)/((1/(PL*PL)+1/(PR*PR))**(1/2)+2*max(1/PL,1/PR)).
*>
*> An approximate bound on x can be computed from DIF(1:2), PL and PR.
*>
*> If y = ( F-norm(E,F) / x) <= 1, the angles between the perturbed
*> (L', R') and unperturbed (L, R) left and right deflating subspaces
*> associated with the selected cluster in the (1,1)-blocks can be
*> bounded as
*>
*> max-angle(L, L') <= arctan( y * PL / (1 - y * (1 - PL * PL)**(1/2))
*> max-angle(R, R') <= arctan( y * PR / (1 - y * (1 - PR * PR)**(1/2))
*>
*> See LAPACK User's Guide section 4.11 or the following references
*> for more information.
*>
*> Note that if the default method for computing the Frobenius-norm-
*> based estimate DIF is not wanted (see SLATDF), then the parameter
*> IDIFJB (see below) should be changed from 3 to 4 (routine SLATDF
*> (IJOB = 2 will be used)). See STGSYL for more details.
*> \endverbatim
*
*> \par Contributors:
* ==================
*>
*> Bo Kagstrom and Peter Poromaa, Department of Computing Science,
*> Umea University, S-901 87 Umea, Sweden.
*
*> \par References:
* ================
*>
*> \verbatim
*>
*> [1] B. Kagstrom; A Direct Method for Reordering Eigenvalues in the
*> Generalized Real Schur Form of a Regular Matrix Pair (A, B), in
*> M.S. Moonen et al (eds), Linear Algebra for Large Scale and
*> Real-Time Applications, Kluwer Academic Publ. 1993, pp 195-218.
*>
*> [2] B. Kagstrom and P. Poromaa; Computing Eigenspaces with Specified
*> Eigenvalues of a Regular Matrix Pair (A, B) and Condition
*> Estimation: Theory, Algorithms and Software,
*> Report UMINF - 94.04, Department of Computing Science, Umea
*> University, S-901 87 Umea, Sweden, 1994. Also as LAPACK Working
*> Note 87. To appear in Numerical Algorithms, 1996.
*>
*> [3] B. Kagstrom and P. Poromaa, LAPACK-Style Algorithms and Software
*> for Solving the Generalized Sylvester Equation and Estimating the
*> Separation between Regular Matrix Pairs, Report UMINF - 93.23,
*> Department of Computing Science, Umea University, S-901 87 Umea,
*> Sweden, December 1993, Revised April 1994, Also as LAPACK Working
*> Note 75. To appear in ACM Trans. on Math. Software, Vol 22, No 1,
*> 1996.
*> \endverbatim
*>
* =====================================================================
SUBROUTINE STGSEN( IJOB, WANTQ, WANTZ, SELECT, N, A, LDA, B, LDB,
$ ALPHAR, ALPHAI, BETA, Q, LDQ, Z, LDZ, M, PL,
$ PR, DIF, WORK, LWORK, IWORK, LIWORK, INFO )
*
* -- LAPACK computational routine --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
* .. Scalar Arguments ..
LOGICAL WANTQ, WANTZ
INTEGER IJOB, INFO, LDA, LDB, LDQ, LDZ, LIWORK, LWORK,
$ M, N
REAL PL, PR
* ..
* .. Array Arguments ..
LOGICAL SELECT( * )
INTEGER IWORK( * )
REAL A( LDA, * ), ALPHAI( * ), ALPHAR( * ),
$ B( LDB, * ), BETA( * ), DIF( * ), Q( LDQ, * ),
$ WORK( * ), Z( LDZ, * )
* ..
*
* =====================================================================
*
* .. Parameters ..
INTEGER IDIFJB
PARAMETER ( IDIFJB = 3 )
REAL ZERO, ONE
PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
* ..
* .. Local Scalars ..
LOGICAL LQUERY, PAIR, SWAP, WANTD, WANTD1, WANTD2,
$ WANTP
INTEGER I, IERR, IJB, K, KASE, KK, KS, LIWMIN, LWMIN,
$ MN2, N1, N2
REAL DSCALE, DSUM, EPS, RDSCAL, SMLNUM
* ..
* .. Local Arrays ..
INTEGER ISAVE( 3 )
* ..
* .. External Subroutines ..
EXTERNAL SLACN2, SLACPY, SLAG2, SLASSQ, STGEXC, STGSYL,
$ XERBLA
* ..
* .. External Functions ..
REAL SLAMCH
EXTERNAL SLAMCH
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, SIGN, SQRT
* ..
* .. Executable Statements ..
*
* Decode and test the input parameters
*
INFO = 0
LQUERY = ( LWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
*
IF( IJOB.LT.0 .OR. IJOB.GT.5 ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -5
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -7
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -9
ELSE IF( LDQ.LT.1 .OR. ( WANTQ .AND. LDQ.LT.N ) ) THEN
INFO = -14
ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
INFO = -16
END IF
*
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'STGSEN', -INFO )
RETURN
END IF
*
* Get machine constants
*
EPS = SLAMCH( 'P' )
SMLNUM = SLAMCH( 'S' ) / EPS
IERR = 0
*
WANTP = IJOB.EQ.1 .OR. IJOB.GE.4
WANTD1 = IJOB.EQ.2 .OR. IJOB.EQ.4
WANTD2 = IJOB.EQ.3 .OR. IJOB.EQ.5
WANTD = WANTD1 .OR. WANTD2
*
* Set M to the dimension of the specified pair of deflating
* subspaces.
*
M = 0
PAIR = .FALSE.
IF( .NOT.LQUERY .OR. IJOB.NE.0 ) THEN
DO 10 K = 1, N
IF( PAIR ) THEN
PAIR = .FALSE.
ELSE
IF( K.LT.N ) THEN
IF( A( K+1, K ).EQ.ZERO ) THEN
IF( SELECT( K ) )
$ M = M + 1
ELSE
PAIR = .TRUE.
IF( SELECT( K ) .OR. SELECT( K+1 ) )
$ M = M + 2
END IF
ELSE
IF( SELECT( N ) )
$ M = M + 1
END IF
END IF
10 CONTINUE
END IF
*
IF( IJOB.EQ.1 .OR. IJOB.EQ.2 .OR. IJOB.EQ.4 ) THEN
LWMIN = MAX( 1, 4*N+16, 2*M*(N-M) )
LIWMIN = MAX( 1, N+6 )
ELSE IF( IJOB.EQ.3 .OR. IJOB.EQ.5 ) THEN
LWMIN = MAX( 1, 4*N+16, 4*M*(N-M) )
LIWMIN = MAX( 1, 2*M*(N-M), N+6 )
ELSE
LWMIN = MAX( 1, 4*N+16 )
LIWMIN = 1
END IF
*
WORK( 1 ) = LWMIN
IWORK( 1 ) = LIWMIN
*
IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
INFO = -22
ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
INFO = -24
END IF
*
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'STGSEN', -INFO )
RETURN
ELSE IF( LQUERY ) THEN
RETURN
END IF
*
* Quick return if possible.
*
IF( M.EQ.N .OR. M.EQ.0 ) THEN
IF( WANTP ) THEN
PL = ONE
PR = ONE
END IF
IF( WANTD ) THEN
DSCALE = ZERO
DSUM = ONE
DO 20 I = 1, N
CALL SLASSQ( N, A( 1, I ), 1, DSCALE, DSUM )
CALL SLASSQ( N, B( 1, I ), 1, DSCALE, DSUM )
20 CONTINUE
DIF( 1 ) = DSCALE*SQRT( DSUM )
DIF( 2 ) = DIF( 1 )
END IF
GO TO 60
END IF
*
* Collect the selected blocks at the top-left corner of (A, B).
*
KS = 0
PAIR = .FALSE.
DO 30 K = 1, N
IF( PAIR ) THEN
PAIR = .FALSE.
ELSE
*
SWAP = SELECT( K )
IF( K.LT.N ) THEN
IF( A( K+1, K ).NE.ZERO ) THEN
PAIR = .TRUE.
SWAP = SWAP .OR. SELECT( K+1 )
END IF
END IF
*
IF( SWAP ) THEN
KS = KS + 1
*
* Swap the K-th block to position KS.
* Perform the reordering of diagonal blocks in (A, B)
* by orthogonal transformation matrices and update
* Q and Z accordingly (if requested):
*
KK = K
IF( K.NE.KS )
$ CALL STGEXC( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
$ Z, LDZ, KK, KS, WORK, LWORK, IERR )
*
IF( IERR.GT.0 ) THEN
*
* Swap is rejected: exit.
*
INFO = 1
IF( WANTP ) THEN
PL = ZERO
PR = ZERO
END IF
IF( WANTD ) THEN
DIF( 1 ) = ZERO
DIF( 2 ) = ZERO
END IF
GO TO 60
END IF
*
IF( PAIR )
$ KS = KS + 1
END IF
END IF
30 CONTINUE
IF( WANTP ) THEN
*
* Solve generalized Sylvester equation for R and L
* and compute PL and PR.
*
N1 = M
N2 = N - M
I = N1 + 1
IJB = 0
CALL SLACPY( 'Full', N1, N2, A( 1, I ), LDA, WORK, N1 )
CALL SLACPY( 'Full', N1, N2, B( 1, I ), LDB, WORK( N1*N2+1 ),
$ N1 )
CALL STGSYL( 'N', IJB, N1, N2, A, LDA, A( I, I ), LDA, WORK,
$ N1, B, LDB, B( I, I ), LDB, WORK( N1*N2+1 ), N1,
$ DSCALE, DIF( 1 ), WORK( N1*N2*2+1 ),
$ LWORK-2*N1*N2, IWORK, IERR )
*
* Estimate the reciprocal of norms of "projections" onto left
* and right eigenspaces.
*
RDSCAL = ZERO
DSUM = ONE
CALL SLASSQ( N1*N2, WORK, 1, RDSCAL, DSUM )
PL = RDSCAL*SQRT( DSUM )
IF( PL.EQ.ZERO ) THEN
PL = ONE
ELSE
PL = DSCALE / ( SQRT( DSCALE*DSCALE / PL+PL )*SQRT( PL ) )
END IF
RDSCAL = ZERO
DSUM = ONE
CALL SLASSQ( N1*N2, WORK( N1*N2+1 ), 1, RDSCAL, DSUM )
PR = RDSCAL*SQRT( DSUM )
IF( PR.EQ.ZERO ) THEN
PR = ONE
ELSE
PR = DSCALE / ( SQRT( DSCALE*DSCALE / PR+PR )*SQRT( PR ) )
END IF
END IF
*
IF( WANTD ) THEN
*
* Compute estimates of Difu and Difl.
*
IF( WANTD1 ) THEN
N1 = M
N2 = N - M
I = N1 + 1
IJB = IDIFJB
*
* Frobenius norm-based Difu-estimate.
*
CALL STGSYL( 'N', IJB, N1, N2, A, LDA, A( I, I ), LDA, WORK,
$ N1, B, LDB, B( I, I ), LDB, WORK( N1*N2+1 ),
$ N1, DSCALE, DIF( 1 ), WORK( 2*N1*N2+1 ),
$ LWORK-2*N1*N2, IWORK, IERR )
*
* Frobenius norm-based Difl-estimate.
*
CALL STGSYL( 'N', IJB, N2, N1, A( I, I ), LDA, A, LDA, WORK,
$ N2, B( I, I ), LDB, B, LDB, WORK( N1*N2+1 ),
$ N2, DSCALE, DIF( 2 ), WORK( 2*N1*N2+1 ),
$ LWORK-2*N1*N2, IWORK, IERR )
ELSE
*
*
* Compute 1-norm-based estimates of Difu and Difl using
* reversed communication with SLACN2. In each step a
* generalized Sylvester equation or a transposed variant
* is solved.
*
KASE = 0
N1 = M
N2 = N - M
I = N1 + 1
IJB = 0
MN2 = 2*N1*N2
*
* 1-norm-based estimate of Difu.
*
40 CONTINUE
CALL SLACN2( MN2, WORK( MN2+1 ), WORK, IWORK, DIF( 1 ),
$ KASE, ISAVE )
IF( KASE.NE.0 ) THEN
IF( KASE.EQ.1 ) THEN
*
* Solve generalized Sylvester equation.
*
CALL STGSYL( 'N', IJB, N1, N2, A, LDA, A( I, I ), LDA,
$ WORK, N1, B, LDB, B( I, I ), LDB,
$ WORK( N1*N2+1 ), N1, DSCALE, DIF( 1 ),
$ WORK( 2*N1*N2+1 ), LWORK-2*N1*N2, IWORK,
$ IERR )
ELSE
*
* Solve the transposed variant.
*
CALL STGSYL( 'T', IJB, N1, N2, A, LDA, A( I, I ), LDA,
$ WORK, N1, B, LDB, B( I, I ), LDB,
$ WORK( N1*N2+1 ), N1, DSCALE, DIF( 1 ),
$ WORK( 2*N1*N2+1 ), LWORK-2*N1*N2, IWORK,
$ IERR )
END IF
GO TO 40
END IF
DIF( 1 ) = DSCALE / DIF( 1 )
*
* 1-norm-based estimate of Difl.
*
50 CONTINUE
CALL SLACN2( MN2, WORK( MN2+1 ), WORK, IWORK, DIF( 2 ),
$ KASE, ISAVE )
IF( KASE.NE.0 ) THEN
IF( KASE.EQ.1 ) THEN
*
* Solve generalized Sylvester equation.
*
CALL STGSYL( 'N', IJB, N2, N1, A( I, I ), LDA, A, LDA,
$ WORK, N2, B( I, I ), LDB, B, LDB,
$ WORK( N1*N2+1 ), N2, DSCALE, DIF( 2 ),
$ WORK( 2*N1*N2+1 ), LWORK-2*N1*N2, IWORK,
$ IERR )
ELSE
*
* Solve the transposed variant.
*
CALL STGSYL( 'T', IJB, N2, N1, A( I, I ), LDA, A, LDA,
$ WORK, N2, B( I, I ), LDB, B, LDB,
$ WORK( N1*N2+1 ), N2, DSCALE, DIF( 2 ),
$ WORK( 2*N1*N2+1 ), LWORK-2*N1*N2, IWORK,
$ IERR )
END IF
GO TO 50
END IF
DIF( 2 ) = DSCALE / DIF( 2 )
*
END IF
END IF
*
60 CONTINUE
*
* Compute generalized eigenvalues of reordered pair (A, B) and
* normalize the generalized Schur form.
*
PAIR = .FALSE.
DO 70 K = 1, N
IF( PAIR ) THEN
PAIR = .FALSE.
ELSE
*
IF( K.LT.N ) THEN
IF( A( K+1, K ).NE.ZERO ) THEN
PAIR = .TRUE.
END IF
END IF
*
IF( PAIR ) THEN
*
* Compute the eigenvalue(s) at position K.
*
WORK( 1 ) = A( K, K )
WORK( 2 ) = A( K+1, K )
WORK( 3 ) = A( K, K+1 )
WORK( 4 ) = A( K+1, K+1 )
WORK( 5 ) = B( K, K )
WORK( 6 ) = B( K+1, K )
WORK( 7 ) = B( K, K+1 )
WORK( 8 ) = B( K+1, K+1 )
CALL SLAG2( WORK, 2, WORK( 5 ), 2, SMLNUM*EPS, BETA( K ),
$ BETA( K+1 ), ALPHAR( K ), ALPHAR( K+1 ),
$ ALPHAI( K ) )
ALPHAI( K+1 ) = -ALPHAI( K )
*
ELSE
*
IF( SIGN( ONE, B( K, K ) ).LT.ZERO ) THEN
*
* If B(K,K) is negative, make it positive
*
DO 80 I = 1, N
A( K, I ) = -A( K, I )
B( K, I ) = -B( K, I )
IF( WANTQ ) Q( I, K ) = -Q( I, K )
80 CONTINUE
END IF
*
ALPHAR( K ) = A( K, K )
ALPHAI( K ) = ZERO
BETA( K ) = B( K, K )
*
END IF
END IF
70 CONTINUE
*
WORK( 1 ) = LWMIN
IWORK( 1 ) = LIWMIN
*
RETURN
*
* End of STGSEN
*
END