      SUBROUTINE SHGEQZ( JOB, COMPQ, COMPZ, N, ILO, IHI, A, LDA, B, LDB,
     $                   ALPHAR, ALPHAI, BETA, Q, LDQ, Z, LDZ, WORK,
     $                   LWORK, INFO )
*
*  -- LAPACK routine (instrumented to count operations, version 3.0) --
*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
*     Courant Institute, Argonne National Lab, and Rice University
*     June 30, 1999
*
*     .. Scalar Arguments ..
      CHARACTER          COMPQ, COMPZ, JOB
      INTEGER            IHI, ILO, INFO, LDA, LDB, LDQ, LDZ, LWORK, N
*     ..
*     .. Array Arguments ..
      REAL               A( LDA, * ), ALPHAI( * ), ALPHAR( * ),
     $                   B( LDB, * ), BETA( * ), Q( LDQ, * ), WORK( * ),
     $                   Z( LDZ, * )
*     ..
*     ---------------------- Begin Timing Code -------------------------
*     Common block to return operation count and iteration count
*     ITCNT is initialized to 0, OPS is only incremented
*     OPST is used to accumulate small contributions to OPS
*     to avoid roundoff error
*     .. Common blocks ..
      COMMON             / LATIME / OPS, ITCNT
*     ..
*     .. Scalars in Common ..
      REAL               ITCNT, OPS
*     ..
*     ----------------------- End Timing Code --------------------------
*
*  Purpose
*  =======
*
*  SHGEQZ implements a single-/double-shift version of the QZ method for
*  finding the generalized eigenvalues
*
*  w(j)=(ALPHAR(j) + i*ALPHAI(j))/BETAR(j)   of the equation
*
*       det( A - w(i) B ) = 0
*
*  In addition, the pair A,B may be reduced to generalized Schur form:
*  B is upper triangular, and A is block upper triangular, where the
*  diagonal blocks are either 1-by-1 or 2-by-2, the 2-by-2 blocks having
*  complex generalized eigenvalues (see the description of the argument
*  JOB.)
*
*  If JOB='S', then the pair (A,B) is simultaneously reduced to Schur
*  form by applying one orthogonal tranformation (usually called Q) on
*  the left and another (usually called Z) on the right.  The 2-by-2
*  upper-triangular diagonal blocks of B corresponding to 2-by-2 blocks
*  of A will be reduced to positive diagonal matrices.  (I.e.,
*  if A(j+1,j) is non-zero, then B(j+1,j)=B(j,j+1)=0 and B(j,j) and
*  B(j+1,j+1) will be positive.)
*
*  If JOB='E', then at each iteration, the same transformations
*  are computed, but they are only applied to those parts of A and B
*  which are needed to compute ALPHAR, ALPHAI, and BETAR.
*
*  If JOB='S' and COMPQ and COMPZ are 'V' or 'I', then the orthogonal
*  transformations used to reduce (A,B) are accumulated into the arrays
*  Q and Z s.t.:
*
*       Q(in) A(in) Z(in)* = Q(out) A(out) Z(out)*
*       Q(in) B(in) Z(in)* = Q(out) B(out) Z(out)*
*
*  Ref: C.B. Moler & G.W. Stewart, "An Algorithm for Generalized Matrix
*       Eigenvalue Problems", SIAM J. Numer. Anal., 10(1973),
*       pp. 241--256.
*
*  Arguments
*  =========
*
*  JOB     (input) CHARACTER*1
*          = 'E': compute only ALPHAR, ALPHAI, and BETA.  A and B will
*                 not necessarily be put into generalized Schur form.
*          = 'S': put A and B into generalized Schur form, as well
*                 as computing ALPHAR, ALPHAI, and BETA.
*
*  COMPQ   (input) CHARACTER*1
*          = 'N': do not modify Q.
*          = 'V': multiply the array Q on the right by the transpose of
*                 the orthogonal tranformation that is applied to the
*                 left side of A and B to reduce them to Schur form.
*          = 'I': like COMPQ='V', except that Q will be initialized to
*                 the identity first.
*
*  COMPZ   (input) CHARACTER*1
*          = 'N': do not modify Z.
*          = 'V': multiply the array Z on the right by the orthogonal
*                 tranformation that is applied to the right side of
*                 A and B to reduce them to Schur form.
*          = 'I': like COMPZ='V', except that Z will be initialized to
*                 the identity first.
*
*  N       (input) INTEGER
*          The order of the matrices A, B, Q, and Z.  N >= 0.
*
*  ILO     (input) INTEGER
*  IHI     (input) INTEGER
*          It is assumed that A is already upper triangular in rows and
*          columns 1:ILO-1 and IHI+1:N.
*          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
*
*  A       (input/output) REAL array, dimension (LDA, N)
*          On entry, the N-by-N upper Hessenberg matrix A.  Elements
*          below the subdiagonal must be zero.
*          If JOB='S', then on exit A and B will have been
*             simultaneously reduced to generalized Schur form.
*          If JOB='E', then on exit A will have been destroyed.
*             The diagonal blocks will be correct, but the off-diagonal
*             portion will be meaningless.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A.  LDA >= max( 1, N ).
*
*  B       (input/output) REAL array, dimension (LDB, N)
*          On entry, the N-by-N upper triangular matrix B.  Elements
*          below the diagonal must be zero.  2-by-2 blocks in B
*          corresponding to 2-by-2 blocks in A will be reduced to
*          positive diagonal form.  (I.e., if A(j+1,j) is non-zero,
*          then B(j+1,j)=B(j,j+1)=0 and B(j,j) and B(j+1,j+1) will be
*          positive.)
*          If JOB='S', then on exit A and B will have been
*             simultaneously reduced to Schur form.
*          If JOB='E', then on exit B will have been destroyed.
*             Elements corresponding to diagonal blocks of A will be
*             correct, but the off-diagonal portion will be meaningless.
*
*  LDB     (input) INTEGER
*          The leading dimension of the array B.  LDB >= max( 1, N ).
*
*  ALPHAR  (output) REAL array, dimension (N)
*          ALPHAR(1:N) will be set to real parts of the diagonal
*          elements of A that would result from reducing A and B to
*          Schur form and then further reducing them both to triangular
*          form using unitary transformations s.t. the diagonal of B
*          was non-negative real.  Thus, if A(j,j) is in a 1-by-1 block
*          (i.e., A(j+1,j)=A(j,j+1)=0), then ALPHAR(j)=A(j,j).
*          Note that the (real or complex) values
*          (ALPHAR(j) + i*ALPHAI(j))/BETA(j), j=1,...,N, are the
*          generalized eigenvalues of the matrix pencil A - wB.
*
*  ALPHAI  (output) REAL array, dimension (N)
*          ALPHAI(1:N) will be set to imaginary parts of the diagonal
*          elements of A that would result from reducing A and B to
*          Schur form and then further reducing them both to triangular
*          form using unitary transformations s.t. the diagonal of B
*          was non-negative real.  Thus, if A(j,j) is in a 1-by-1 block
*          (i.e., A(j+1,j)=A(j,j+1)=0), then ALPHAR(j)=0.
*          Note that the (real or complex) values
*          (ALPHAR(j) + i*ALPHAI(j))/BETA(j), j=1,...,N, are the
*          generalized eigenvalues of the matrix pencil A - wB.
*
*  BETA    (output) REAL array, dimension (N)
*          BETA(1:N) will be set to the (real) diagonal elements of B
*          that would result from reducing A and B to Schur form and
*          then further reducing them both to triangular form using
*          unitary transformations s.t. the diagonal of B was
*          non-negative real.  Thus, if A(j,j) is in a 1-by-1 block
*          (i.e., A(j+1,j)=A(j,j+1)=0), then BETA(j)=B(j,j).
*          Note that the (real or complex) values
*          (ALPHAR(j) + i*ALPHAI(j))/BETA(j), j=1,...,N, are the
*          generalized eigenvalues of the matrix pencil A - wB.
*          (Note that BETA(1:N) will always be non-negative, and no
*          BETAI is necessary.)
*
*  Q       (input/output) REAL array, dimension (LDQ, N)
*          If COMPQ='N', then Q will not be referenced.
*          If COMPQ='V' or 'I', then the transpose of the orthogonal
*             transformations which are applied to A and B on the left
*             will be applied to the array Q on the right.
*
*  LDQ     (input) INTEGER
*          The leading dimension of the array Q.  LDQ >= 1.
*          If COMPQ='V' or 'I', then LDQ >= N.
*
*  Z       (input/output) REAL array, dimension (LDZ, N)
*          If COMPZ='N', then Z will not be referenced.
*          If COMPZ='V' or 'I', then the orthogonal transformations
*             which are applied to A and B on the right will be applied
*             to the array Z on the right.
*
*  LDZ     (input) INTEGER
*          The leading dimension of the array Z.  LDZ >= 1.
*          If COMPZ='V' or 'I', then LDZ >= N.
*
*  WORK    (workspace/output) REAL array, dimension (LWORK)
*          On exit, if INFO >= 0, WORK(1) returns the optimal LWORK.
*
*  LWORK   (input) INTEGER
*          The dimension of the array WORK.  LWORK >= max(1,N).
*
*          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.
*
*  INFO    (output) INTEGER
*          = 0: successful exit
*          < 0: if INFO = -i, the i-th argument had an illegal value
*          = 1,...,N: the QZ iteration did not converge.  (A,B) is not
*                     in Schur form, but ALPHAR(i), ALPHAI(i), and
*                     BETA(i), i=INFO+1,...,N should be correct.
*          = N+1,...,2*N: the shift calculation failed.  (A,B) is not
*                     in Schur form, but ALPHAR(i), ALPHAI(i), and
*                     BETA(i), i=INFO-N+1,...,N should be correct.
*          > 2*N:     various "impossible" errors.
*
*  Further Details
*  ===============
*
*  Iteration counters:
*
*  JITER  -- counts iterations.
*  IITER  -- counts iterations run since ILAST was last
*            changed.  This is therefore reset only when a 1-by-1 or
*            2-by-2 block deflates off the bottom.
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               HALF, ZERO, ONE, SAFETY
      PARAMETER          ( HALF = 0.5E+0, ZERO = 0.0E+0, ONE = 1.0E+0,
     $                   SAFETY = 1.0E+2 )
*     ..
*     .. Local Scalars ..
      LOGICAL            ILAZR2, ILAZRO, ILPIVT, ILQ, ILSCHR, ILZ,
     $                   LQUERY
      INTEGER            ICOMPQ, ICOMPZ, IFIRST, IFRSTM, IITER, ILAST,
     $                   ILASTM, IN, ISCHUR, ISTART, J, JC, JCH, JITER,
     $                   JR, MAXIT, NQ, NZ
      REAL               A11, A12, A1I, A1R, A21, A22, A2I, A2R, AD11,
     $                   AD11L, AD12, AD12L, AD21, AD21L, AD22, AD22L,
     $                   AD32L, AN, ANORM, ASCALE, ATOL, B11, B1A, B1I,
     $                   B1R, B22, B2A, B2I, B2R, BN, BNORM, BSCALE,
     $                   BTOL, C, C11I, C11R, C12, C21, C22I, C22R, CL,
     $                   CQ, CR, CZ, ESHIFT, OPST, S, S1, S1INV, S2,
     $                   SAFMAX, SAFMIN, SCALE, SL, SQI, SQR, SR, SZI,
     $                   SZR, T, TAU, TEMP, TEMP2, TEMPI, TEMPR, U1,
     $                   U12, U12L, U2, ULP, VS, W11, W12, W21, W22,
     $                   WABS, WI, WR, WR2
*     ..
*     .. Local Arrays ..
      REAL               V( 3 )
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      REAL               SLAMCH, SLANHS, SLAPY2, SLAPY3
      EXTERNAL           LSAME, SLAMCH, SLANHS, SLAPY2, SLAPY3
*     ..
*     .. External Subroutines ..
      EXTERNAL           SLAG2, SLARFG, SLARTG, SLASET, SLASV2, SROT,
     $                   XERBLA
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS, MAX, MIN, REAL, SQRT
*     ..
*     .. Executable Statements ..
*
*     Decode JOB, COMPQ, COMPZ
*
      IF( LSAME( JOB, 'E' ) ) THEN
         ILSCHR = .FALSE.
         ISCHUR = 1
      ELSE IF( LSAME( JOB, 'S' ) ) THEN
         ILSCHR = .TRUE.
         ISCHUR = 2
      ELSE
         ISCHUR = 0
      END IF
*
      IF( LSAME( COMPQ, 'N' ) ) THEN
         ILQ = .FALSE.
         ICOMPQ = 1
         NQ = 0
      ELSE IF( LSAME( COMPQ, 'V' ) ) THEN
         ILQ = .TRUE.
         ICOMPQ = 2
         NQ = N
      ELSE IF( LSAME( COMPQ, 'I' ) ) THEN
         ILQ = .TRUE.
         ICOMPQ = 3
         NQ = N
      ELSE
         ICOMPQ = 0
      END IF
*
      IF( LSAME( COMPZ, 'N' ) ) THEN
         ILZ = .FALSE.
         ICOMPZ = 1
         NZ = 0
      ELSE IF( LSAME( COMPZ, 'V' ) ) THEN
         ILZ = .TRUE.
         ICOMPZ = 2
         NZ = N
      ELSE IF( LSAME( COMPZ, 'I' ) ) THEN
         ILZ = .TRUE.
         ICOMPZ = 3
         NZ = N
      ELSE
         ICOMPZ = 0
      END IF
*
*     Check Argument Values
*
      INFO = 0
      WORK( 1 ) = MAX( 1, N )
      LQUERY = ( LWORK.EQ.-1 )
      IF( ISCHUR.EQ.0 ) THEN
         INFO = -1
      ELSE IF( ICOMPQ.EQ.0 ) THEN
         INFO = -2
      ELSE IF( ICOMPZ.EQ.0 ) THEN
         INFO = -3
      ELSE IF( N.LT.0 ) THEN
         INFO = -4
      ELSE IF( ILO.LT.1 ) THEN
         INFO = -5
      ELSE IF( IHI.GT.N .OR. IHI.LT.ILO-1 ) THEN
         INFO = -6
      ELSE IF( LDA.LT.N ) THEN
         INFO = -8
      ELSE IF( LDB.LT.N ) THEN
         INFO = -10
      ELSE IF( LDQ.LT.1 .OR. ( ILQ .AND. LDQ.LT.N ) ) THEN
         INFO = -15
      ELSE IF( LDZ.LT.1 .OR. ( ILZ .AND. LDZ.LT.N ) ) THEN
         INFO = -17
      ELSE IF( LWORK.LT.MAX( 1, N ) .AND. .NOT.LQUERY ) THEN
         INFO = -19
      END IF
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'SHGEQZ', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
*
*     Quick return if possible
*
      IF( N.LE.0 ) THEN
         WORK( 1 ) = REAL( 1 )
*        --------------------- Begin Timing Code -----------------------
         ITCNT = ZERO
*        ---------------------- End Timing Code ------------------------
         RETURN
      END IF
*
*     Initialize Q and Z
*
      IF( ICOMPQ.EQ.3 )
     $   CALL SLASET( 'Full', N, N, ZERO, ONE, Q, LDQ )
      IF( ICOMPZ.EQ.3 )
     $   CALL SLASET( 'Full', N, N, ZERO, ONE, Z, LDZ )
*
*     Machine Constants
*
      IN = IHI + 1 - ILO
      SAFMIN = SLAMCH( 'S' )
      SAFMAX = ONE / SAFMIN
      ULP = SLAMCH( 'E' )*SLAMCH( 'B' )
      ANORM = SLANHS( 'F', IN, A( ILO, ILO ), LDA, WORK )
      BNORM = SLANHS( 'F', IN, B( ILO, ILO ), LDB, WORK )
      ATOL = MAX( SAFMIN, ULP*ANORM )
      BTOL = MAX( SAFMIN, ULP*BNORM )
      ASCALE = ONE / MAX( SAFMIN, ANORM )
      BSCALE = ONE / MAX( SAFMIN, BNORM )
*
*     Set Eigenvalues IHI+1:N
*
      DO 30 J = IHI + 1, N
         IF( B( J, J ).LT.ZERO ) THEN
            IF( ILSCHR ) THEN
               DO 10 JR = 1, J
                  A( JR, J ) = -A( JR, J )
                  B( JR, J ) = -B( JR, J )
   10          CONTINUE
            ELSE
               A( J, J ) = -A( J, J )
               B( J, J ) = -B( J, J )
            END IF
            IF( ILZ ) THEN
               DO 20 JR = 1, N
                  Z( JR, J ) = -Z( JR, J )
   20          CONTINUE
            END IF
         END IF
         ALPHAR( J ) = A( J, J )
         ALPHAI( J ) = ZERO
         BETA( J ) = B( J, J )
   30 CONTINUE
*
*     ---------------------- Begin Timing Code -------------------------
*     Count ops for norms, etc.
      OPST = ZERO
      OPS = OPS + REAL( 2*N**2+6*N )
*     ----------------------- End Timing Code --------------------------
*
*
*     If IHI < ILO, skip QZ steps
*
      IF( IHI.LT.ILO )
     $   GO TO 380
*
*     MAIN QZ ITERATION LOOP
*
*     Initialize dynamic indices
*
*     Eigenvalues ILAST+1:N have been found.
*        Column operations modify rows IFRSTM:whatever.
*        Row operations modify columns whatever:ILASTM.
*
*     If only eigenvalues are being computed, then
*        IFRSTM is the row of the last splitting row above row ILAST;
*        this is always at least ILO.
*     IITER counts iterations since the last eigenvalue was found,
*        to tell when to use an extraordinary shift.
*     MAXIT is the maximum number of QZ sweeps allowed.
*
      ILAST = IHI
      IF( ILSCHR ) THEN
         IFRSTM = 1
         ILASTM = N
      ELSE
         IFRSTM = ILO
         ILASTM = IHI
      END IF
      IITER = 0
      ESHIFT = ZERO
      MAXIT = 30*( IHI-ILO+1 )
*
      DO 360 JITER = 1, MAXIT
*
*        Split the matrix if possible.
*
*        Two tests:
*           1: A(j,j-1)=0  or  j=ILO
*           2: B(j,j)=0
*
         IF( ILAST.EQ.ILO ) THEN
*
*           Special case: j=ILAST
*
            GO TO 80
         ELSE
            IF( ABS( A( ILAST, ILAST-1 ) ).LE.ATOL ) THEN
               A( ILAST, ILAST-1 ) = ZERO
               GO TO 80
            END IF
         END IF
*
         IF( ABS( B( ILAST, ILAST ) ).LE.BTOL ) THEN
            B( ILAST, ILAST ) = ZERO
            GO TO 70
         END IF
*
*        General case: j<ILAST
*
         DO 60 J = ILAST - 1, ILO, -1
*
*           Test 1: for A(j,j-1)=0 or j=ILO
*
            IF( J.EQ.ILO ) THEN
               ILAZRO = .TRUE.
            ELSE
               IF( ABS( A( J, J-1 ) ).LE.ATOL ) THEN
                  A( J, J-1 ) = ZERO
                  ILAZRO = .TRUE.
               ELSE
                  ILAZRO = .FALSE.
               END IF
            END IF
*
*           Test 2: for B(j,j)=0
*
            IF( ABS( B( J, J ) ).LT.BTOL ) THEN
               B( J, J ) = ZERO
*
*              Test 1a: Check for 2 consecutive small subdiagonals in A
*
               ILAZR2 = .FALSE.
               IF( .NOT.ILAZRO ) THEN
                  TEMP = ABS( A( J, J-1 ) )
                  TEMP2 = ABS( A( J, J ) )
                  TEMPR = MAX( TEMP, TEMP2 )
                  IF( TEMPR.LT.ONE .AND. TEMPR.NE.ZERO ) THEN
                     TEMP = TEMP / TEMPR
                     TEMP2 = TEMP2 / TEMPR
                  END IF
                  IF( TEMP*( ASCALE*ABS( A( J+1, J ) ) ).LE.TEMP2*
     $                ( ASCALE*ATOL ) )ILAZR2 = .TRUE.
               END IF
*
*              If both tests pass (1 & 2), i.e., the leading diagonal
*              element of B in the block is zero, split a 1x1 block off
*              at the top. (I.e., at the J-th row/column) The leading
*              diagonal element of the remainder can also be zero, so
*              this may have to be done repeatedly.
*
               IF( ILAZRO .OR. ILAZR2 ) THEN
                  DO 40 JCH = J, ILAST - 1
                     TEMP = A( JCH, JCH )
                     CALL SLARTG( TEMP, A( JCH+1, JCH ), C, S,
     $                            A( JCH, JCH ) )
                     A( JCH+1, JCH ) = ZERO
                     CALL SROT( ILASTM-JCH, A( JCH, JCH+1 ), LDA,
     $                          A( JCH+1, JCH+1 ), LDA, C, S )
                     CALL SROT( ILASTM-JCH, B( JCH, JCH+1 ), LDB,
     $                          B( JCH+1, JCH+1 ), LDB, C, S )
                     IF( ILQ )
     $                  CALL SROT( N, Q( 1, JCH ), 1, Q( 1, JCH+1 ), 1,
     $                             C, S )
                     IF( ILAZR2 )
     $                  A( JCH, JCH-1 ) = A( JCH, JCH-1 )*C
                     ILAZR2 = .FALSE.
*
*                    --------------- Begin Timing Code -----------------
                     OPST = OPST + REAL( 7+12*( ILASTM-JCH )+6*NQ )
*                    ---------------- End Timing Code ------------------
*
                     IF( ABS( B( JCH+1, JCH+1 ) ).GE.BTOL ) THEN
                        IF( JCH+1.GE.ILAST ) THEN
                           GO TO 80
                        ELSE
                           IFIRST = JCH + 1
                           GO TO 110
                        END IF
                     END IF
                     B( JCH+1, JCH+1 ) = ZERO
   40             CONTINUE
                  GO TO 70
               ELSE
*
*                 Only test 2 passed -- chase the zero to B(ILAST,ILAST)
*                 Then process as in the case B(ILAST,ILAST)=0
*
                  DO 50 JCH = J, ILAST - 1
                     TEMP = B( JCH, JCH+1 )
                     CALL SLARTG( TEMP, B( JCH+1, JCH+1 ), C, S,
     $                            B( JCH, JCH+1 ) )
                     B( JCH+1, JCH+1 ) = ZERO
                     IF( JCH.LT.ILASTM-1 )
     $                  CALL SROT( ILASTM-JCH-1, B( JCH, JCH+2 ), LDB,
     $                             B( JCH+1, JCH+2 ), LDB, C, S )
                     CALL SROT( ILASTM-JCH+2, A( JCH, JCH-1 ), LDA,
     $                          A( JCH+1, JCH-1 ), LDA, C, S )
                     IF( ILQ )
     $                  CALL SROT( N, Q( 1, JCH ), 1, Q( 1, JCH+1 ), 1,
     $                             C, S )
                     TEMP = A( JCH+1, JCH )
                     CALL SLARTG( TEMP, A( JCH+1, JCH-1 ), C, S,
     $                            A( JCH+1, JCH ) )
                     A( JCH+1, JCH-1 ) = ZERO
                     CALL SROT( JCH+1-IFRSTM, A( IFRSTM, JCH ), 1,
     $                          A( IFRSTM, JCH-1 ), 1, C, S )
                     CALL SROT( JCH-IFRSTM, B( IFRSTM, JCH ), 1,
     $                          B( IFRSTM, JCH-1 ), 1, C, S )
                     IF( ILZ )
     $                  CALL SROT( N, Z( 1, JCH ), 1, Z( 1, JCH-1 ), 1,
     $                             C, S )
   50             CONTINUE
*
*                 ---------------- Begin Timing Code -------------------
                  OPST = OPST + REAL( 26+12*( ILASTM-IFRSTM )+6*
     $                   ( NQ+NZ ) )*REAL( ILAST-J )
*                 ----------------- End Timing Code --------------------
*
                  GO TO 70
               END IF
            ELSE IF( ILAZRO ) THEN
*
*              Only test 1 passed -- work on J:ILAST
*
               IFIRST = J
               GO TO 110
            END IF
*
*           Neither test passed -- try next J
*
   60    CONTINUE
*
*        (Drop-through is "impossible")
*
         INFO = N + 1
         GO TO 420
*
*        B(ILAST,ILAST)=0 -- clear A(ILAST,ILAST-1) to split off a
*        1x1 block.
*
   70    CONTINUE
         TEMP = A( ILAST, ILAST )
         CALL SLARTG( TEMP, A( ILAST, ILAST-1 ), C, S,
     $                A( ILAST, ILAST ) )
         A( ILAST, ILAST-1 ) = ZERO
         CALL SROT( ILAST-IFRSTM, A( IFRSTM, ILAST ), 1,
     $              A( IFRSTM, ILAST-1 ), 1, C, S )
         CALL SROT( ILAST-IFRSTM, B( IFRSTM, ILAST ), 1,
     $              B( IFRSTM, ILAST-1 ), 1, C, S )
         IF( ILZ )
     $      CALL SROT( N, Z( 1, ILAST ), 1, Z( 1, ILAST-1 ), 1, C, S )
*
*        --------------------- Begin Timing Code -----------------------
         OPST = OPST + REAL( 7+12*( ILAST-IFRSTM )+6*NZ )
*        ---------------------- End Timing Code ------------------------
*
*
*        A(ILAST,ILAST-1)=0 -- Standardize B, set ALPHAR, ALPHAI,
*                              and BETA
*
   80    CONTINUE
         IF( B( ILAST, ILAST ).LT.ZERO ) THEN
            IF( ILSCHR ) THEN
               DO 90 J = IFRSTM, ILAST
                  A( J, ILAST ) = -A( J, ILAST )
                  B( J, ILAST ) = -B( J, ILAST )
   90          CONTINUE
            ELSE
               A( ILAST, ILAST ) = -A( ILAST, ILAST )
               B( ILAST, ILAST ) = -B( ILAST, ILAST )
            END IF
            IF( ILZ ) THEN
               DO 100 J = 1, N
                  Z( J, ILAST ) = -Z( J, ILAST )
  100          CONTINUE
            END IF
         END IF
         ALPHAR( ILAST ) = A( ILAST, ILAST )
         ALPHAI( ILAST ) = ZERO
         BETA( ILAST ) = B( ILAST, ILAST )
*
*        Go to next block -- exit if finished.
*
         ILAST = ILAST - 1
         IF( ILAST.LT.ILO )
     $      GO TO 380
*
*        Reset counters
*
         IITER = 0
         ESHIFT = ZERO
         IF( .NOT.ILSCHR ) THEN
            ILASTM = ILAST
            IF( IFRSTM.GT.ILAST )
     $         IFRSTM = ILO
         END IF
         GO TO 350
*
*        QZ step
*
*        This iteration only involves rows/columns IFIRST:ILAST. We
*        assume IFIRST < ILAST, and that the diagonal of B is non-zero.
*
  110    CONTINUE
         IITER = IITER + 1
         IF( .NOT.ILSCHR ) THEN
            IFRSTM = IFIRST
         END IF
*
*        Compute single shifts.
*
*        At this point, IFIRST < ILAST, and the diagonal elements of
*        B(IFIRST:ILAST,IFIRST,ILAST) are larger than BTOL (in
*        magnitude)
*
         IF( ( IITER / 10 )*10.EQ.IITER ) THEN
*
*           Exceptional shift.  Chosen for no particularly good reason.
*           (Single shift only.)
*
            IF( ( REAL( MAXIT )*SAFMIN )*ABS( A( ILAST-1, ILAST ) ).LT.
     $          ABS( B( ILAST-1, ILAST-1 ) ) ) THEN
               ESHIFT = ESHIFT + A( ILAST-1, ILAST ) /
     $                  B( ILAST-1, ILAST-1 )
            ELSE
               ESHIFT = ESHIFT + ONE / ( SAFMIN*REAL( MAXIT ) )
            END IF
            S1 = ONE
            WR = ESHIFT
*
*           ------------------- Begin Timing Code ----------------------
            OPST = OPST + REAL( 4 )
*           -------------------- End Timing Code -----------------------
*
         ELSE
*
*           Shifts based on the generalized eigenvalues of the
*           bottom-right 2x2 block of A and B. The first eigenvalue
*           returned by SLAG2 is the Wilkinson shift (AEP p.512),
*
            CALL SLAG2( A( ILAST-1, ILAST-1 ), LDA,
     $                  B( ILAST-1, ILAST-1 ), LDB, SAFMIN*SAFETY, S1,
     $                  S2, WR, WR2, WI )
*
            TEMP = MAX( S1, SAFMIN*MAX( ONE, ABS( WR ), ABS( WI ) ) )
*
*           ------------------- Begin Timing Code ----------------------
            OPST = OPST + REAL( 57 )
*           -------------------- End Timing Code -----------------------
*
            IF( WI.NE.ZERO )
     $         GO TO 200
         END IF
*
*        Fiddle with shift to avoid overflow
*
         TEMP = MIN( ASCALE, ONE )*( HALF*SAFMAX )
         IF( S1.GT.TEMP ) THEN
            SCALE = TEMP / S1
         ELSE
            SCALE = ONE
         END IF
*
         TEMP = MIN( BSCALE, ONE )*( HALF*SAFMAX )
         IF( ABS( WR ).GT.TEMP )
     $      SCALE = MIN( SCALE, TEMP / ABS( WR ) )
         S1 = SCALE*S1
         WR = SCALE*WR
*
*        Now check for two consecutive small subdiagonals.
*
         DO 120 J = ILAST - 1, IFIRST + 1, -1
            ISTART = J
            TEMP = ABS( S1*A( J, J-1 ) )
            TEMP2 = ABS( S1*A( J, J )-WR*B( J, J ) )
            TEMPR = MAX( TEMP, TEMP2 )
            IF( TEMPR.LT.ONE .AND. TEMPR.NE.ZERO ) THEN
               TEMP = TEMP / TEMPR
               TEMP2 = TEMP2 / TEMPR
            END IF
            IF( ABS( ( ASCALE*A( J+1, J ) )*TEMP ).LE.( ASCALE*ATOL )*
     $          TEMP2 )GO TO 130
  120    CONTINUE
*
         ISTART = IFIRST
  130    CONTINUE
*
*        Do an implicit single-shift QZ sweep.
*
*        Initial Q
*
         TEMP = S1*A( ISTART, ISTART ) - WR*B( ISTART, ISTART )
         TEMP2 = S1*A( ISTART+1, ISTART )
         CALL SLARTG( TEMP, TEMP2, C, S, TEMPR )
*
*        Sweep
*
         DO 190 J = ISTART, ILAST - 1
            IF( J.GT.ISTART ) THEN
               TEMP = A( J, J-1 )
               CALL SLARTG( TEMP, A( J+1, J-1 ), C, S, A( J, J-1 ) )
               A( J+1, J-1 ) = ZERO
            END IF
*
            DO 140 JC = J, ILASTM
               TEMP = C*A( J, JC ) + S*A( J+1, JC )
               A( J+1, JC ) = -S*A( J, JC ) + C*A( J+1, JC )
               A( J, JC ) = TEMP
               TEMP2 = C*B( J, JC ) + S*B( J+1, JC )
               B( J+1, JC ) = -S*B( J, JC ) + C*B( J+1, JC )
               B( J, JC ) = TEMP2
  140       CONTINUE
            IF( ILQ ) THEN
               DO 150 JR = 1, N
                  TEMP = C*Q( JR, J ) + S*Q( JR, J+1 )
                  Q( JR, J+1 ) = -S*Q( JR, J ) + C*Q( JR, J+1 )
                  Q( JR, J ) = TEMP
  150          CONTINUE
            END IF
*
            TEMP = B( J+1, J+1 )
            CALL SLARTG( TEMP, B( J+1, J ), C, S, B( J+1, J+1 ) )
            B( J+1, J ) = ZERO
*
            DO 160 JR = IFRSTM, MIN( J+2, ILAST )
               TEMP = C*A( JR, J+1 ) + S*A( JR, J )
               A( JR, J ) = -S*A( JR, J+1 ) + C*A( JR, J )
               A( JR, J+1 ) = TEMP
  160       CONTINUE
            DO 170 JR = IFRSTM, J
               TEMP = C*B( JR, J+1 ) + S*B( JR, J )
               B( JR, J ) = -S*B( JR, J+1 ) + C*B( JR, J )
               B( JR, J+1 ) = TEMP
  170       CONTINUE
            IF( ILZ ) THEN
               DO 180 JR = 1, N
                  TEMP = C*Z( JR, J+1 ) + S*Z( JR, J )
                  Z( JR, J ) = -S*Z( JR, J+1 ) + C*Z( JR, J )
                  Z( JR, J+1 ) = TEMP
  180          CONTINUE
            END IF
  190    CONTINUE
*
*        --------------------- Begin Timing Code -----------------------
         OPST = OPST + REAL( 6+( ILAST-ISTART )*
     $          ( 8+14+36+12*( ILASTM-IFRSTM )+6*( NQ+NZ ) ) )
*        ---------------------- End Timing Code ------------------------
*
         GO TO 350
*
*        Use Francis double-shift
*
*        Note: the Francis double-shift should work with real shifts,
*              but only if the block is at least 3x3.
*              This code may break if this point is reached with
*              a 2x2 block with real eigenvalues.
*
  200    CONTINUE
         IF( IFIRST+1.EQ.ILAST ) THEN
*
*           Special case -- 2x2 block with complex eigenvectors
*
*           Step 1: Standardize, that is, rotate so that
*
*                       ( B11  0  )
*                   B = (         )  with B11 non-negative.
*                       (  0  B22 )
*
            CALL SLASV2( B( ILAST-1, ILAST-1 ), B( ILAST-1, ILAST ),
     $                   B( ILAST, ILAST ), B22, B11, SR, CR, SL, CL )
*
            IF( B11.LT.ZERO ) THEN
               CR = -CR
               SR = -SR
               B11 = -B11
               B22 = -B22
            END IF
*
            CALL SROT( ILASTM+1-IFIRST, A( ILAST-1, ILAST-1 ), LDA,
     $                 A( ILAST, ILAST-1 ), LDA, CL, SL )
            CALL SROT( ILAST+1-IFRSTM, A( IFRSTM, ILAST-1 ), 1,
     $                 A( IFRSTM, ILAST ), 1, CR, SR )
*
            IF( ILAST.LT.ILASTM )
     $         CALL SROT( ILASTM-ILAST, B( ILAST-1, ILAST+1 ), LDB,
     $                    B( ILAST, ILAST+1 ), LDA, CL, SL )
            IF( IFRSTM.LT.ILAST-1 )
     $         CALL SROT( IFIRST-IFRSTM, B( IFRSTM, ILAST-1 ), 1,
     $                    B( IFRSTM, ILAST ), 1, CR, SR )
*
            IF( ILQ )
     $         CALL SROT( N, Q( 1, ILAST-1 ), 1, Q( 1, ILAST ), 1, CL,
     $                    SL )
            IF( ILZ )
     $         CALL SROT( N, Z( 1, ILAST-1 ), 1, Z( 1, ILAST ), 1, CR,
     $                    SR )
*
            B( ILAST-1, ILAST-1 ) = B11
            B( ILAST-1, ILAST ) = ZERO
            B( ILAST, ILAST-1 ) = ZERO
            B( ILAST, ILAST ) = B22
*
*           If B22 is negative, negate column ILAST
*
            IF( B22.LT.ZERO ) THEN
               DO 210 J = IFRSTM, ILAST
                  A( J, ILAST ) = -A( J, ILAST )
                  B( J, ILAST ) = -B( J, ILAST )
  210          CONTINUE
*
               IF( ILZ ) THEN
                  DO 220 J = 1, N
                     Z( J, ILAST ) = -Z( J, ILAST )
  220             CONTINUE
               END IF
            END IF
*
*           Step 2: Compute ALPHAR, ALPHAI, and BETA (see refs.)
*
*           Recompute shift
*
            CALL SLAG2( A( ILAST-1, ILAST-1 ), LDA,
     $                  B( ILAST-1, ILAST-1 ), LDB, SAFMIN*SAFETY, S1,
     $                  TEMP, WR, TEMP2, WI )
*
*           ------------------- Begin Timing Code ----------------------
            OPST = OPST + REAL( 103+12*( ILASTM+ILAST-IFIRST-IFRSTM )+6*
     $             ( NQ+NZ ) )
*           -------------------- End Timing Code -----------------------
*
*           If standardization has perturbed the shift onto real line,
*           do another (real single-shift) QR step.
*
            IF( WI.EQ.ZERO )
     $         GO TO 350
            S1INV = ONE / S1
*
*           Do EISPACK (QZVAL) computation of alpha and beta
*
            A11 = A( ILAST-1, ILAST-1 )
            A21 = A( ILAST, ILAST-1 )
            A12 = A( ILAST-1, ILAST )
            A22 = A( ILAST, ILAST )
*
*           Compute complex Givens rotation on right
*           (Assume some element of C = (sA - wB) > unfl )
*                            __
*           (sA - wB) ( CZ   -SZ )
*                     ( SZ    CZ )
*
            C11R = S1*A11 - WR*B11
            C11I = -WI*B11
            C12 = S1*A12
            C21 = S1*A21
            C22R = S1*A22 - WR*B22
            C22I = -WI*B22
*
            IF( ABS( C11R )+ABS( C11I )+ABS( C12 ).GT.ABS( C21 )+
     $          ABS( C22R )+ABS( C22I ) ) THEN
               T = SLAPY3( C12, C11R, C11I )
               CZ = C12 / T
               SZR = -C11R / T
               SZI = -C11I / T
            ELSE
               CZ = SLAPY2( C22R, C22I )
               IF( CZ.LE.SAFMIN ) THEN
                  CZ = ZERO
                  SZR = ONE
                  SZI = ZERO
               ELSE
                  TEMPR = C22R / CZ
                  TEMPI = C22I / CZ
                  T = SLAPY2( CZ, C21 )
                  CZ = CZ / T
                  SZR = -C21*TEMPR / T
                  SZI = C21*TEMPI / T
               END IF
            END IF
*
*           Compute Givens rotation on left
*
*           (  CQ   SQ )
*           (  __      )  A or B
*           ( -SQ   CQ )
*
            AN = ABS( A11 ) + ABS( A12 ) + ABS( A21 ) + ABS( A22 )
            BN = ABS( B11 ) + ABS( B22 )
            WABS = ABS( WR ) + ABS( WI )
            IF( S1*AN.GT.WABS*BN ) THEN
               CQ = CZ*B11
               SQR = SZR*B22
               SQI = -SZI*B22
            ELSE
               A1R = CZ*A11 + SZR*A12
               A1I = SZI*A12
               A2R = CZ*A21 + SZR*A22
               A2I = SZI*A22
               CQ = SLAPY2( A1R, A1I )
               IF( CQ.LE.SAFMIN ) THEN
                  CQ = ZERO
                  SQR = ONE
                  SQI = ZERO
               ELSE
                  TEMPR = A1R / CQ
                  TEMPI = A1I / CQ
                  SQR = TEMPR*A2R + TEMPI*A2I
                  SQI = TEMPI*A2R - TEMPR*A2I
               END IF
            END IF
            T = SLAPY3( CQ, SQR, SQI )
            CQ = CQ / T
            SQR = SQR / T
            SQI = SQI / T
*
*           Compute diagonal elements of QBZ
*
            TEMPR = SQR*SZR - SQI*SZI
            TEMPI = SQR*SZI + SQI*SZR
            B1R = CQ*CZ*B11 + TEMPR*B22
            B1I = TEMPI*B22
            B1A = SLAPY2( B1R, B1I )
            B2R = CQ*CZ*B22 + TEMPR*B11
            B2I = -TEMPI*B11
            B2A = SLAPY2( B2R, B2I )
*
*           Normalize so beta > 0, and Im( alpha1 ) > 0
*
            BETA( ILAST-1 ) = B1A
            BETA( ILAST ) = B2A
            ALPHAR( ILAST-1 ) = ( WR*B1A )*S1INV
            ALPHAI( ILAST-1 ) = ( WI*B1A )*S1INV
            ALPHAR( ILAST ) = ( WR*B2A )*S1INV
            ALPHAI( ILAST ) = -( WI*B2A )*S1INV
*
*           ------------------- Begin Timing Code ----------------------
            OPST = OPST + REAL( 93 )
*           -------------------- End Timing Code -----------------------
*
*           Step 3: Go to next block -- exit if finished.
*
            ILAST = IFIRST - 1
            IF( ILAST.LT.ILO )
     $         GO TO 380
*
*           Reset counters
*
            IITER = 0
            ESHIFT = ZERO
            IF( .NOT.ILSCHR ) THEN
               ILASTM = ILAST
               IF( IFRSTM.GT.ILAST )
     $            IFRSTM = ILO
            END IF
            GO TO 350
         ELSE
*
*           Usual case: 3x3 or larger block, using Francis implicit
*                       double-shift
*
*                                    2
*           Eigenvalue equation is  w  - c w + d = 0,
*
*                                         -1 2        -1
*           so compute 1st column of  (A B  )  - c A B   + d
*           using the formula in QZIT (from EISPACK)
*
*           We assume that the block is at least 3x3
*
            AD11 = ( ASCALE*A( ILAST-1, ILAST-1 ) ) /
     $             ( BSCALE*B( ILAST-1, ILAST-1 ) )
            AD21 = ( ASCALE*A( ILAST, ILAST-1 ) ) /
     $             ( BSCALE*B( ILAST-1, ILAST-1 ) )
            AD12 = ( ASCALE*A( ILAST-1, ILAST ) ) /
     $             ( BSCALE*B( ILAST, ILAST ) )
            AD22 = ( ASCALE*A( ILAST, ILAST ) ) /
     $             ( BSCALE*B( ILAST, ILAST ) )
            U12 = B( ILAST-1, ILAST ) / B( ILAST, ILAST )
            AD11L = ( ASCALE*A( IFIRST, IFIRST ) ) /
     $              ( BSCALE*B( IFIRST, IFIRST ) )
            AD21L = ( ASCALE*A( IFIRST+1, IFIRST ) ) /
     $              ( BSCALE*B( IFIRST, IFIRST ) )
            AD12L = ( ASCALE*A( IFIRST, IFIRST+1 ) ) /
     $              ( BSCALE*B( IFIRST+1, IFIRST+1 ) )
            AD22L = ( ASCALE*A( IFIRST+1, IFIRST+1 ) ) /
     $              ( BSCALE*B( IFIRST+1, IFIRST+1 ) )
            AD32L = ( ASCALE*A( IFIRST+2, IFIRST+1 ) ) /
     $              ( BSCALE*B( IFIRST+1, IFIRST+1 ) )
            U12L = B( IFIRST, IFIRST+1 ) / B( IFIRST+1, IFIRST+1 )
*
            V( 1 ) = ( AD11-AD11L )*( AD22-AD11L ) - AD12*AD21 +
     $               AD21*U12*AD11L + ( AD12L-AD11L*U12L )*AD21L
            V( 2 ) = ( ( AD22L-AD11L )-AD21L*U12L-( AD11-AD11L )-
     $               ( AD22-AD11L )+AD21*U12 )*AD21L
            V( 3 ) = AD32L*AD21L
*
            ISTART = IFIRST
*
            CALL SLARFG( 3, V( 1 ), V( 2 ), 1, TAU )
            V( 1 ) = ONE
*
*           Sweep
*
            DO 290 J = ISTART, ILAST - 2
*
*              All but last elements: use 3x3 Householder transforms.
*
*              Zero (j-1)st column of A
*
               IF( J.GT.ISTART ) THEN
                  V( 1 ) = A( J, J-1 )
                  V( 2 ) = A( J+1, J-1 )
                  V( 3 ) = A( J+2, J-1 )
*
                  CALL SLARFG( 3, A( J, J-1 ), V( 2 ), 1, TAU )
                  V( 1 ) = ONE
                  A( J+1, J-1 ) = ZERO
                  A( J+2, J-1 ) = ZERO
               END IF
*
               DO 230 JC = J, ILASTM
                  TEMP = TAU*( A( J, JC )+V( 2 )*A( J+1, JC )+V( 3 )*
     $                   A( J+2, JC ) )
                  A( J, JC ) = A( J, JC ) - TEMP
                  A( J+1, JC ) = A( J+1, JC ) - TEMP*V( 2 )
                  A( J+2, JC ) = A( J+2, JC ) - TEMP*V( 3 )
                  TEMP2 = TAU*( B( J, JC )+V( 2 )*B( J+1, JC )+V( 3 )*
     $                    B( J+2, JC ) )
                  B( J, JC ) = B( J, JC ) - TEMP2
                  B( J+1, JC ) = B( J+1, JC ) - TEMP2*V( 2 )
                  B( J+2, JC ) = B( J+2, JC ) - TEMP2*V( 3 )
  230          CONTINUE
               IF( ILQ ) THEN
                  DO 240 JR = 1, N
                     TEMP = TAU*( Q( JR, J )+V( 2 )*Q( JR, J+1 )+V( 3 )*
     $                      Q( JR, J+2 ) )
                     Q( JR, J ) = Q( JR, J ) - TEMP
                     Q( JR, J+1 ) = Q( JR, J+1 ) - TEMP*V( 2 )
                     Q( JR, J+2 ) = Q( JR, J+2 ) - TEMP*V( 3 )
  240             CONTINUE
               END IF
*
*              Zero j-th column of B (see SLAGBC for details)
*
*              Swap rows to pivot
*
               ILPIVT = .FALSE.
               TEMP = MAX( ABS( B( J+1, J+1 ) ), ABS( B( J+1, J+2 ) ) )
               TEMP2 = MAX( ABS( B( J+2, J+1 ) ), ABS( B( J+2, J+2 ) ) )
               IF( MAX( TEMP, TEMP2 ).LT.SAFMIN ) THEN
                  SCALE = ZERO
                  U1 = ONE
                  U2 = ZERO
                  GO TO 250
               ELSE IF( TEMP.GE.TEMP2 ) THEN
                  W11 = B( J+1, J+1 )
                  W21 = B( J+2, J+1 )
                  W12 = B( J+1, J+2 )
                  W22 = B( J+2, J+2 )
                  U1 = B( J+1, J )
                  U2 = B( J+2, J )
               ELSE
                  W21 = B( J+1, J+1 )
                  W11 = B( J+2, J+1 )
                  W22 = B( J+1, J+2 )
                  W12 = B( J+2, J+2 )
                  U2 = B( J+1, J )
                  U1 = B( J+2, J )
               END IF
*
*              Swap columns if nec.
*
               IF( ABS( W12 ).GT.ABS( W11 ) ) THEN
                  ILPIVT = .TRUE.
                  TEMP = W12
                  TEMP2 = W22
                  W12 = W11
                  W22 = W21
                  W11 = TEMP
                  W21 = TEMP2
               END IF
*
*              LU-factor
*
               TEMP = W21 / W11
               U2 = U2 - TEMP*U1
               W22 = W22 - TEMP*W12
               W21 = ZERO
*
*              Compute SCALE
*
               SCALE = ONE
               IF( ABS( W22 ).LT.SAFMIN ) THEN
                  SCALE = ZERO
                  U2 = ONE
                  U1 = -W12 / W11
                  GO TO 250
               END IF
               IF( ABS( W22 ).LT.ABS( U2 ) )
     $            SCALE = ABS( W22 / U2 )
               IF( ABS( W11 ).LT.ABS( U1 ) )
     $            SCALE = MIN( SCALE, ABS( W11 / U1 ) )
*
*              Solve
*
               U2 = ( SCALE*U2 ) / W22
               U1 = ( SCALE*U1-W12*U2 ) / W11
*
  250          CONTINUE
               IF( ILPIVT ) THEN
                  TEMP = U2
                  U2 = U1
                  U1 = TEMP
               END IF
*
*              Compute Householder Vector
*
               T = SQRT( SCALE**2+U1**2+U2**2 )
               TAU = ONE + SCALE / T
               VS = -ONE / ( SCALE+T )
               V( 1 ) = ONE
               V( 2 ) = VS*U1
               V( 3 ) = VS*U2
*
*              Apply transformations from the right.
*
               DO 260 JR = IFRSTM, MIN( J+3, ILAST )
                  TEMP = TAU*( A( JR, J )+V( 2 )*A( JR, J+1 )+V( 3 )*
     $                   A( JR, J+2 ) )
                  A( JR, J ) = A( JR, J ) - TEMP
                  A( JR, J+1 ) = A( JR, J+1 ) - TEMP*V( 2 )
                  A( JR, J+2 ) = A( JR, J+2 ) - TEMP*V( 3 )
  260          CONTINUE
               DO 270 JR = IFRSTM, J + 2
                  TEMP = TAU*( B( JR, J )+V( 2 )*B( JR, J+1 )+V( 3 )*
     $                   B( JR, J+2 ) )
                  B( JR, J ) = B( JR, J ) - TEMP
                  B( JR, J+1 ) = B( JR, J+1 ) - TEMP*V( 2 )
                  B( JR, J+2 ) = B( JR, J+2 ) - TEMP*V( 3 )
  270          CONTINUE
               IF( ILZ ) THEN
                  DO 280 JR = 1, N
                     TEMP = TAU*( Z( JR, J )+V( 2 )*Z( JR, J+1 )+V( 3 )*
     $                      Z( JR, J+2 ) )
                     Z( JR, J ) = Z( JR, J ) - TEMP
                     Z( JR, J+1 ) = Z( JR, J+1 ) - TEMP*V( 2 )
                     Z( JR, J+2 ) = Z( JR, J+2 ) - TEMP*V( 3 )
  280             CONTINUE
               END IF
               B( J+1, J ) = ZERO
               B( J+2, J ) = ZERO
  290       CONTINUE
*
*           Last elements: Use Givens rotations
*
*           Rotations from the left
*
            J = ILAST - 1
            TEMP = A( J, J-1 )
            CALL SLARTG( TEMP, A( J+1, J-1 ), C, S, A( J, J-1 ) )
            A( J+1, J-1 ) = ZERO
*
            DO 300 JC = J, ILASTM
               TEMP = C*A( J, JC ) + S*A( J+1, JC )
               A( J+1, JC ) = -S*A( J, JC ) + C*A( J+1, JC )
               A( J, JC ) = TEMP
               TEMP2 = C*B( J, JC ) + S*B( J+1, JC )
               B( J+1, JC ) = -S*B( J, JC ) + C*B( J+1, JC )
               B( J, JC ) = TEMP2
  300       CONTINUE
            IF( ILQ ) THEN
               DO 310 JR = 1, N
                  TEMP = C*Q( JR, J ) + S*Q( JR, J+1 )
                  Q( JR, J+1 ) = -S*Q( JR, J ) + C*Q( JR, J+1 )
                  Q( JR, J ) = TEMP
  310          CONTINUE
            END IF
*
*           Rotations from the right.
*
            TEMP = B( J+1, J+1 )
            CALL SLARTG( TEMP, B( J+1, J ), C, S, B( J+1, J+1 ) )
            B( J+1, J ) = ZERO
*
            DO 320 JR = IFRSTM, ILAST
               TEMP = C*A( JR, J+1 ) + S*A( JR, J )
               A( JR, J ) = -S*A( JR, J+1 ) + C*A( JR, J )
               A( JR, J+1 ) = TEMP
  320       CONTINUE
            DO 330 JR = IFRSTM, ILAST - 1
               TEMP = C*B( JR, J+1 ) + S*B( JR, J )
               B( JR, J ) = -S*B( JR, J+1 ) + C*B( JR, J )
               B( JR, J+1 ) = TEMP
  330       CONTINUE
            IF( ILZ ) THEN
               DO 340 JR = 1, N
                  TEMP = C*Z( JR, J+1 ) + S*Z( JR, J )
                  Z( JR, J ) = -S*Z( JR, J+1 ) + C*Z( JR, J )
                  Z( JR, J+1 ) = TEMP
  340          CONTINUE
            END IF
*
*           ------------------- Begin Timing Code ----------------------
            OPST = OPST + ( REAL( 14+30-10+52+12*( ILASTM-IFRSTM )+6*
     $             ( NQ+NZ ) )+REAL( ILAST-1-ISTART )*
     $             REAL( 14+24+90+20*( ILASTM-IFRSTM )+10*( NQ+NZ ) ) )
*           -------------------- End Timing Code -----------------------
*
*           End of Double-Shift code
*
         END IF
*
         GO TO 350
*
*        End of iteration loop
*
  350    CONTINUE
*        --------------------- Begin Timing Code -----------------------
         OPS = OPS + OPST
         OPST = ZERO
*        ---------------------- End Timing Code ------------------------
*
*
  360 CONTINUE
*
*     Drop-through = non-convergence
*
  370 CONTINUE
*     ---------------------- Begin Timing Code -------------------------
      OPS = OPS + OPST
      OPST = ZERO
*     ----------------------- End Timing Code --------------------------
*
      INFO = ILAST
      GO TO 420
*
*     Successful completion of all QZ steps
*
  380 CONTINUE
*
*     Set Eigenvalues 1:ILO-1
*
      DO 410 J = 1, ILO - 1
         IF( B( J, J ).LT.ZERO ) THEN
            IF( ILSCHR ) THEN
               DO 390 JR = 1, J
                  A( JR, J ) = -A( JR, J )
                  B( JR, J ) = -B( JR, J )
  390          CONTINUE
            ELSE
               A( J, J ) = -A( J, J )
               B( J, J ) = -B( J, J )
            END IF
            IF( ILZ ) THEN
               DO 400 JR = 1, N
                  Z( JR, J ) = -Z( JR, J )
  400          CONTINUE
            END IF
         END IF
         ALPHAR( J ) = A( J, J )
         ALPHAI( J ) = ZERO
         BETA( J ) = B( J, J )
  410 CONTINUE
*
*     Normal Termination
*
      INFO = 0
*
*     Exit (other than argument error) -- return optimal workspace size
*
  420 CONTINUE
*
*     ---------------------- Begin Timing Code -------------------------
      OPS = OPS + OPST
      OPST = ZERO
      ITCNT = JITER
*     ----------------------- End Timing Code --------------------------
*
      WORK( 1 ) = REAL( N )
      RETURN
*
*     End of SHGEQZ
*
      END
