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+      SUBROUTINE ZTGSEN( IJOB, WANTQ, WANTZ, SELECT, N, A, LDA, B, LDB,
+     $                   ALPHA, BETA, Q, LDQ, Z, LDZ, M, PL, PR, DIF,
+     $                   WORK, LWORK, IWORK, LIWORK, INFO )
+*
+*  -- LAPACK routine (version 3.1) --
+*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
+*     November 2006
+*
+*     Modified to call ZLACN2 in place of ZLACON, 10 Feb 03, SJH.
+*
+*     .. Scalar Arguments ..
+      LOGICAL            WANTQ, WANTZ
+      INTEGER            IJOB, INFO, LDA, LDB, LDQ, LDZ, LIWORK, LWORK,
+     $                   M, N
+      DOUBLE PRECISION   PL, PR
+*     ..
+*     .. Array Arguments ..
+      LOGICAL            SELECT( * )
+      INTEGER            IWORK( * )
+      DOUBLE PRECISION   DIF( * )
+      COMPLEX*16         A( LDA, * ), ALPHA( * ), B( LDB, * ),
+     $                   BETA( * ), Q( LDQ, * ), WORK( * ), Z( LDZ, * )
+*     ..
+*
+*  Purpose
+*  =======
+*
+*  ZTGSEN reorders the generalized Schur decomposition of a complex
+*  matrix pair (A, B) (in terms of an unitary equivalence trans-
+*  formation Q' * (A, B) * Z), so that a selected cluster of eigenvalues
+*  appears in the leading diagonal blocks of the pair (A,B). The leading
+*  columns of Q and Z form unitary bases of the corresponding left and
+*  right eigenspaces (deflating subspaces). (A, B) must be in
+*  generalized Schur canonical form, that is, A and B are both upper
+*  triangular.
+*
+*  ZTGSEN also computes the generalized eigenvalues
+*
+*           w(j)= ALPHA(j) / BETA(j)
+*
+*  of the reordered matrix pair (A, B).
+*
+*  Optionally, the routine computes 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.
+*
+*
+*  Arguments
+*  =========
+*
+*  IJOB    (input) 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)
+*
+*  WANTQ   (input) LOGICAL
+*          .TRUE. : update the left transformation matrix Q;
+*          .FALSE.: do not update Q.
+*
+*  WANTZ   (input) LOGICAL
+*          .TRUE. : update the right transformation matrix Z;
+*          .FALSE.: do not update Z.
+*
+*  SELECT  (input) LOGICAL array, dimension (N)
+*          SELECT specifies the eigenvalues in the selected cluster. To
+*          select an eigenvalue w(j), SELECT(j) must be set to
+*          .TRUE..
+*
+*  N       (input) INTEGER
+*          The order of the matrices A and B. N >= 0.
+*
+*  A       (input/output) COMPLEX*16 array, dimension(LDA,N)
+*          On entry, the upper triangular matrix A, in generalized
+*          Schur canonical form.
+*          On exit, A is overwritten by the reordered matrix A.
+*
+*  LDA     (input) INTEGER
+*          The leading dimension of the array A. LDA >= max(1,N).
+*
+*  B       (input/output) COMPLEX*16 array, dimension(LDB,N)
+*          On entry, the upper triangular matrix B, in generalized
+*          Schur canonical form.
+*          On exit, B is overwritten by the reordered matrix B.
+*
+*  LDB     (input) INTEGER
+*          The leading dimension of the array B. LDB >= max(1,N).
+*
+*  ALPHA   (output) COMPLEX*16 array, dimension (N)
+*  BETA    (output) COMPLEX*16 array, dimension (N)
+*          The diagonal elements of A and B, respectively,
+*          when the pair (A,B) has been reduced to generalized Schur
+*          form.  ALPHA(i)/BETA(i) i=1,...,N are the generalized
+*          eigenvalues.
+*
+*  Q       (input/output) COMPLEX*16 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 unitary
+*          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.
+*
+*  LDQ     (input) INTEGER
+*          The leading dimension of the array Q. LDQ >= 1.
+*          If WANTQ = .TRUE., LDQ >= N.
+*
+*  Z       (input/output) COMPLEX*16 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 unitary
+*          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.
+*
+*  LDZ     (input) INTEGER
+*          The leading dimension of the array Z. LDZ >= 1.
+*          If WANTZ = .TRUE., LDZ >= N.
+*
+*  M       (output) INTEGER
+*          The dimension of the specified pair of left and right
+*          eigenspaces, (deflating subspaces) 0 <= M <= N.
+*
+*  PL      (output) DOUBLE PRECISION
+*  PR      (output) DOUBLE PRECISION
+*          If IJOB = 1, 4 or 5, PL, PR are lower bounds on the
+*          reciprocal  of the norm of "projections" onto left and right
+*          eigenspace 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, PR are not referenced.
+*
+*  DIF     (output) DOUBLE PRECISION 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, computed using reversed
+*          communication with ZLACN2.
+*          If M = 0 or N, DIF(1:2) = F-norm([A, B]).
+*          If IJOB = 0 or 1, DIF is not referenced.
+*
+*  WORK    (workspace/output) COMPLEX*16 array, dimension (MAX(1,LWORK))
+*          IF IJOB = 0, WORK is not referenced.  Otherwise,
+*          on exit, if INFO = 0, WORK(1) returns the optimal LWORK.
+*
+*  LWORK   (input) INTEGER
+*          The dimension of the array WORK. LWORK >=  1
+*          If IJOB = 1, 2 or 4, LWORK >=  2*M*(N-M)
+*          If IJOB = 3 or 5, LWORK >=  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.
+*
+*  IWORK   (workspace/output) INTEGER array, dimension (MAX(1,LIWORK))
+*          IF IJOB = 0, IWORK is not referenced.  Otherwise,
+*          on exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
+*
+*  LIWORK  (input) INTEGER
+*          The dimension of the array IWORK. LIWORK >= 1.
+*          If IJOB = 1, 2 or 4, LIWORK >=  N+2;
+*          If IJOB = 3 or 5, LIWORK >= MAX(N+2, 2*M*(N-M));
+*
+*          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.
+*
+*  INFO    (output) 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.
+*
+*
+*  Further Details
+*  ===============
+*
+*  ZTGSEN first collects the selected eigenvalues by computing unitary
+*  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'*(A, B)*W = (A11 A12) (B11 B12) n1
+*                              ( 0  A22),( 0  B22) n2
+*                                n1  n2    n1  n2
+*
+*  where N = n1+n2 and U' means the conjugate 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', then the
+*  reordered generalized Schur form of (C, D) is given by
+*
+*           (C, D) = (Q*U)*(U'*(A, B)*W)*(Z*W)',
+*
+*  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', In1) ]
+*            [ kron(In2, B11)  -kron(B22', In1) ].
+*
+*  Here, Inx is the identity matrix of size nx and A22' 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 ZLATDF), then the parameter
+*  IDIFJB (see below) should be changed from 3 to 4 (routine ZLATDF
+*  (IJOB = 2 will be used)). See ZTGSYL for more details.
+*
+*  Based on contributions by
+*     Bo Kagstrom and Peter Poromaa, Department of Computing Science,
+*     Umea University, S-901 87 Umea, Sweden.
+*
+*  References
+*  ==========
+*
+*  [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.
+*
+*  =====================================================================
+*
+*     .. Parameters ..
+      INTEGER            IDIFJB
+      PARAMETER          ( IDIFJB = 3 )
+      DOUBLE PRECISION   ZERO, ONE
+      PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
+*     ..
+*     .. Local Scalars ..
+      LOGICAL            LQUERY, SWAP, WANTD, WANTD1, WANTD2, WANTP
+      INTEGER            I, IERR, IJB, K, KASE, KS, LIWMIN, LWMIN, MN2,
+     $                   N1, N2
+      DOUBLE PRECISION   DSCALE, DSUM, RDSCAL, SAFMIN
+*     ..
+*     .. Local Arrays ..
+      INTEGER            ISAVE( 3 )
+*     ..
+*     .. External Subroutines ..
+      EXTERNAL           XERBLA, ZLACN2, ZLACPY, ZLASSQ, ZSCAL, ZTGEXC,
+     $                   ZTGSYL
+*     ..
+*     .. Intrinsic Functions ..
+      INTRINSIC          ABS, DCMPLX, DCONJG, MAX, SQRT
+*     ..
+*     .. External Functions ..
+      DOUBLE PRECISION   DLAMCH
+      EXTERNAL           DLAMCH
+*     ..
+*     .. 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 = -13
+      ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
+         INFO = -15
+      END IF
+*
+      IF( INFO.NE.0 ) THEN
+         CALL XERBLA( 'ZTGSEN', -INFO )
+         RETURN
+      END IF
+*
+      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
+      DO 10 K = 1, N
+         ALPHA( K ) = A( K, K )
+         BETA( K ) = B( K, K )
+         IF( K.LT.N ) THEN
+            IF( SELECT( K ) )
+     $         M = M + 1
+         ELSE
+            IF( SELECT( N ) )
+     $         M = M + 1
+         END IF
+   10 CONTINUE
+*
+      IF( IJOB.EQ.1 .OR. IJOB.EQ.2 .OR. IJOB.EQ.4 ) THEN
+         LWMIN = MAX( 1, 2*M*( N-M ) )
+         LIWMIN = MAX( 1, N+2 )
+      ELSE IF( IJOB.EQ.3 .OR. IJOB.EQ.5 ) THEN
+         LWMIN = MAX( 1, 4*M*( N-M ) )
+         LIWMIN = MAX( 1, 2*M*( N-M ), N+2 )
+      ELSE
+         LWMIN = 1
+         LIWMIN = 1
+      END IF
+*
+      WORK( 1 ) = LWMIN
+      IWORK( 1 ) = LIWMIN
+*
+      IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
+         INFO = -21
+      ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
+         INFO = -23
+      END IF
+*
+      IF( INFO.NE.0 ) THEN
+         CALL XERBLA( 'ZTGSEN', -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 ZLASSQ( N, A( 1, I ), 1, DSCALE, DSUM )
+               CALL ZLASSQ( N, B( 1, I ), 1, DSCALE, DSUM )
+   20       CONTINUE
+            DIF( 1 ) = DSCALE*SQRT( DSUM )
+            DIF( 2 ) = DIF( 1 )
+         END IF
+         GO TO 70
+      END IF
+*
+*     Get machine constant
+*
+      SAFMIN = DLAMCH( 'S' )
+*
+*     Collect the selected blocks at the top-left corner of (A, B).
+*
+      KS = 0
+      DO 30 K = 1, N
+         SWAP = SELECT( K )
+         IF( SWAP ) THEN
+            KS = KS + 1
+*
+*           Swap the K-th block to position KS. Compute unitary Q
+*           and Z that will swap adjacent diagonal blocks in (A, B).
+*
+            IF( K.NE.KS )
+     $         CALL ZTGEXC( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
+     $                      LDZ, K, KS, 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 70
+            END IF
+         END IF
+   30 CONTINUE
+      IF( WANTP ) THEN
+*
+*        Solve generalized Sylvester equation for R and L:
+*                   A11 * R - L * A22 = A12
+*                   B11 * R - L * B22 = B12
+*
+         N1 = M
+         N2 = N - M
+         I = N1 + 1
+         CALL ZLACPY( 'Full', N1, N2, A( 1, I ), LDA, WORK, N1 )
+         CALL ZLACPY( 'Full', N1, N2, B( 1, I ), LDB, WORK( N1*N2+1 ),
+     $                N1 )
+         IJB = 0
+         CALL ZTGSYL( '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 ZLASSQ( 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 ZLASSQ( 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 Difu and Difl.
+*
+         IF( WANTD1 ) THEN
+            N1 = M
+            N2 = N - M
+            I = N1 + 1
+            IJB = IDIFJB
+*
+*           Frobenius norm-based Difu estimate.
+*
+            CALL ZTGSYL( '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 )
+*
+*           Frobenius norm-based Difl estimate.
+*
+            CALL ZTGSYL( '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( N1*N2*2+1 ),
+     $                   LWORK-2*N1*N2, IWORK, IERR )
+         ELSE
+*
+*           Compute 1-norm-based estimates of Difu and Difl using
+*           reversed communication with ZLACN2. 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 ZLACN2( MN2, WORK( MN2+1 ), WORK, DIF( 1 ), KASE,
+     $                   ISAVE )
+            IF( KASE.NE.0 ) THEN
+               IF( KASE.EQ.1 ) THEN
+*
+*                 Solve generalized Sylvester equation
+*
+                  CALL ZTGSYL( '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 )
+               ELSE
+*
+*                 Solve the transposed variant.
+*
+                  CALL ZTGSYL( 'C', 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 )
+               END IF
+               GO TO 40
+            END IF
+            DIF( 1 ) = DSCALE / DIF( 1 )
+*
+*           1-norm-based estimate of Difl.
+*
+   50       CONTINUE
+            CALL ZLACN2( MN2, WORK( MN2+1 ), WORK, DIF( 2 ), KASE,
+     $                   ISAVE )
+            IF( KASE.NE.0 ) THEN
+               IF( KASE.EQ.1 ) THEN
+*
+*                 Solve generalized Sylvester equation
+*
+                  CALL ZTGSYL( '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( N1*N2*2+1 ), LWORK-2*N1*N2, IWORK,
+     $                         IERR )
+               ELSE
+*
+*                 Solve the transposed variant.
+*
+                  CALL ZTGSYL( 'C', IJB, N2, N1, A( I, I ), LDA, A, LDA,
+     $                         WORK, N2, B, LDB, B( I, I ), LDB,
+     $                         WORK( N1*N2+1 ), N2, DSCALE, DIF( 2 ),
+     $                         WORK( N1*N2*2+1 ), LWORK-2*N1*N2, IWORK,
+     $                         IERR )
+               END IF
+               GO TO 50
+            END IF
+            DIF( 2 ) = DSCALE / DIF( 2 )
+         END IF
+      END IF
+*
+*     If B(K,K) is complex, make it real and positive (normalization
+*     of the generalized Schur form) and Store the generalized
+*     eigenvalues of reordered pair (A, B)
+*
+      DO 60 K = 1, N
+         DSCALE = ABS( B( K, K ) )
+         IF( DSCALE.GT.SAFMIN ) THEN
+            WORK( 1 ) = DCONJG( B( K, K ) / DSCALE )
+            WORK( 2 ) = B( K, K ) / DSCALE
+            B( K, K ) = DSCALE
+            CALL ZSCAL( N-K, WORK( 1 ), B( K, K+1 ), LDB )
+            CALL ZSCAL( N-K+1, WORK( 1 ), A( K, K ), LDA )
+            IF( WANTQ )
+     $         CALL ZSCAL( N, WORK( 2 ), Q( 1, K ), 1 )
+         ELSE
+            B( K, K ) = DCMPLX( ZERO, ZERO )
+         END IF
+*
+         ALPHA( K ) = A( K, K )
+         BETA( K ) = B( K, K )
+*
+   60 CONTINUE
+*
+   70 CONTINUE
+*
+      WORK( 1 ) = LWMIN
+      IWORK( 1 ) = LIWMIN
+*
+      RETURN
+*
+*     End of ZTGSEN
+*
+      END