Move LAPACK trunk into position.

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+      SUBROUTINE ZTRSEN( JOB, COMPQ, SELECT, N, T, LDT, Q, LDQ, W, M, S,
+     $                   SEP, WORK, LWORK, 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 ..
+      CHARACTER          COMPQ, JOB
+      INTEGER            INFO, LDQ, LDT, LWORK, M, N
+      DOUBLE PRECISION   S, SEP
+*     ..
+*     .. Array Arguments ..
+      LOGICAL            SELECT( * )
+      COMPLEX*16         Q( LDQ, * ), T( LDT, * ), W( * ), WORK( * )
+*     ..
+*
+*  Purpose
+*  =======
+*
+*  ZTRSEN reorders the Schur factorization of a complex matrix
+*  A = Q*T*Q**H, so that a selected cluster of eigenvalues appears in
+*  the leading positions on the diagonal of the upper triangular matrix
+*  T, and the leading columns of Q form an orthonormal basis of the
+*  corresponding right invariant subspace.
+*
+*  Optionally the routine computes the reciprocal condition numbers of
+*  the cluster of eigenvalues and/or the invariant subspace.
+*
+*  Arguments
+*  =========
+*
+*  JOB     (input) CHARACTER*1
+*          Specifies whether condition numbers are required for the
+*          cluster of eigenvalues (S) or the invariant subspace (SEP):
+*          = 'N': none;
+*          = 'E': for eigenvalues only (S);
+*          = 'V': for invariant subspace only (SEP);
+*          = 'B': for both eigenvalues and invariant subspace (S and
+*                 SEP).
+*
+*  COMPQ   (input) CHARACTER*1
+*          = 'V': update the matrix Q of Schur vectors;
+*          = 'N': do not update Q.
+*
+*  SELECT  (input) LOGICAL array, dimension (N)
+*          SELECT specifies the eigenvalues in the selected cluster. To
+*          select the j-th eigenvalue, SELECT(j) must be set to .TRUE..
+*
+*  N       (input) INTEGER
+*          The order of the matrix T. N >= 0.
+*
+*  T       (input/output) COMPLEX*16 array, dimension (LDT,N)
+*          On entry, the upper triangular matrix T.
+*          On exit, T is overwritten by the reordered matrix T, with the
+*          selected eigenvalues as the leading diagonal elements.
+*
+*  LDT     (input) INTEGER
+*          The leading dimension of the array T. LDT >= max(1,N).
+*
+*  Q       (input/output) COMPLEX*16 array, dimension (LDQ,N)
+*          On entry, if COMPQ = 'V', the matrix Q of Schur vectors.
+*          On exit, if COMPQ = 'V', Q has been postmultiplied by the
+*          unitary transformation matrix which reorders T; the leading M
+*          columns of Q form an orthonormal basis for the specified
+*          invariant subspace.
+*          If COMPQ = 'N', Q is not referenced.
+*
+*  LDQ     (input) INTEGER
+*          The leading dimension of the array Q.
+*          LDQ >= 1; and if COMPQ = 'V', LDQ >= N.
+*
+*  W       (output) COMPLEX*16 array, dimension (N)
+*          The reordered eigenvalues of T, in the same order as they
+*          appear on the diagonal of T.
+*
+*  M       (output) INTEGER
+*          The dimension of the specified invariant subspace.
+*          0 <= M <= N.
+*
+*  S       (output) DOUBLE PRECISION
+*          If JOB = 'E' or 'B', S is a lower bound on the reciprocal
+*          condition number for the selected cluster of eigenvalues.
+*          S cannot underestimate the true reciprocal condition number
+*          by more than a factor of sqrt(N). If M = 0 or N, S = 1.
+*          If JOB = 'N' or 'V', S is not referenced.
+*
+*  SEP     (output) DOUBLE PRECISION
+*          If JOB = 'V' or 'B', SEP is the estimated reciprocal
+*          condition number of the specified invariant subspace. If
+*          M = 0 or N, SEP = norm(T).
+*          If JOB = 'N' or 'E', SEP is not referenced.
+*
+*  WORK    (workspace/output) COMPLEX*16 array, dimension (MAX(1,LWORK))
+*          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
+*
+*  LWORK   (input) INTEGER
+*          The dimension of the array WORK.
+*          If JOB = 'N', LWORK >= 1;
+*          if JOB = 'E', LWORK = max(1,M*(N-M));
+*          if JOB = 'V' or 'B', LWORK >= max(1,2*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.
+*
+*  INFO    (output) INTEGER
+*          = 0:  successful exit
+*          < 0:  if INFO = -i, the i-th argument had an illegal value
+*
+*  Further Details
+*  ===============
+*
+*  ZTRSEN first collects the selected eigenvalues by computing a unitary
+*  transformation Z to move them to the top left corner of T. In other
+*  words, the selected eigenvalues are the eigenvalues of T11 in:
+*
+*                Z'*T*Z = ( T11 T12 ) n1
+*                         (  0  T22 ) n2
+*                            n1  n2
+*
+*  where N = n1+n2 and Z' means the conjugate transpose of Z. The first
+*  n1 columns of Z span the specified invariant subspace of T.
+*
+*  If T has been obtained from the Schur factorization of a matrix
+*  A = Q*T*Q', then the reordered Schur factorization of A is given by
+*  A = (Q*Z)*(Z'*T*Z)*(Q*Z)', and the first n1 columns of Q*Z span the
+*  corresponding invariant subspace of A.
+*
+*  The reciprocal condition number of the average of the eigenvalues of
+*  T11 may be returned in S. S lies between 0 (very badly conditioned)
+*  and 1 (very well conditioned). It is computed as follows. First we
+*  compute R so that
+*
+*                         P = ( I  R ) n1
+*                             ( 0  0 ) n2
+*                               n1 n2
+*
+*  is the projector on the invariant subspace associated with T11.
+*  R is the solution of the Sylvester equation:
+*
+*                        T11*R - R*T22 = T12.
+*
+*  Let F-norm(M) denote the Frobenius-norm of M and 2-norm(M) denote
+*  the two-norm of M. Then S is computed as the lower bound
+*
+*                      (1 + F-norm(R)**2)**(-1/2)
+*
+*  on the reciprocal of 2-norm(P), the true reciprocal condition number.
+*  S cannot underestimate 1 / 2-norm(P) by more than a factor of
+*  sqrt(N).
+*
+*  An approximate error bound for the computed average of the
+*  eigenvalues of T11 is
+*
+*                         EPS * norm(T) / S
+*
+*  where EPS is the machine precision.
+*
+*  The reciprocal condition number of the right invariant subspace
+*  spanned by the first n1 columns of Z (or of Q*Z) is returned in SEP.
+*  SEP is defined as the separation of T11 and T22:
+*
+*                     sep( T11, T22 ) = sigma-min( C )
+*
+*  where sigma-min(C) is the smallest singular value of the
+*  n1*n2-by-n1*n2 matrix
+*
+*     C  = kprod( I(n2), T11 ) - kprod( transpose(T22), I(n1) )
+*
+*  I(m) is an m by m identity matrix, and kprod denotes the Kronecker
+*  product. We estimate sigma-min(C) by the reciprocal of an estimate of
+*  the 1-norm of inverse(C). The true reciprocal 1-norm of inverse(C)
+*  cannot differ from sigma-min(C) by more than a factor of sqrt(n1*n2).
+*
+*  When SEP is small, small changes in T can cause large changes in
+*  the invariant subspace. An approximate bound on the maximum angular
+*  error in the computed right invariant subspace is
+*
+*                      EPS * norm(T) / SEP
+*
+*  =====================================================================
+*
+*     .. Parameters ..
+      DOUBLE PRECISION   ZERO, ONE
+      PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
+*     ..
+*     .. Local Scalars ..
+      LOGICAL            LQUERY, WANTBH, WANTQ, WANTS, WANTSP
+      INTEGER            IERR, K, KASE, KS, LWMIN, N1, N2, NN
+      DOUBLE PRECISION   EST, RNORM, SCALE
+*     ..
+*     .. Local Arrays ..
+      INTEGER            ISAVE( 3 )
+      DOUBLE PRECISION   RWORK( 1 )
+*     ..
+*     .. External Functions ..
+      LOGICAL            LSAME
+      DOUBLE PRECISION   ZLANGE
+      EXTERNAL           LSAME, ZLANGE
+*     ..
+*     .. External Subroutines ..
+      EXTERNAL           XERBLA, ZLACN2, ZLACPY, ZTREXC, ZTRSYL
+*     ..
+*     .. Intrinsic Functions ..
+      INTRINSIC          MAX, SQRT
+*     ..
+*     .. Executable Statements ..
+*
+*     Decode and test the input parameters.
+*
+      WANTBH = LSAME( JOB, 'B' )
+      WANTS = LSAME( JOB, 'E' ) .OR. WANTBH
+      WANTSP = LSAME( JOB, 'V' ) .OR. WANTBH
+      WANTQ = LSAME( COMPQ, 'V' )
+*
+*     Set M to the number of selected eigenvalues.
+*
+      M = 0
+      DO 10 K = 1, N
+         IF( SELECT( K ) )
+     $      M = M + 1
+   10 CONTINUE
+*
+      N1 = M
+      N2 = N - M
+      NN = N1*N2
+*
+      INFO = 0
+      LQUERY = ( LWORK.EQ.-1 )
+*
+      IF( WANTSP ) THEN
+         LWMIN = MAX( 1, 2*NN )
+      ELSE IF( LSAME( JOB, 'N' ) ) THEN
+         LWMIN = 1
+      ELSE IF( LSAME( JOB, 'E' ) ) THEN
+         LWMIN = MAX( 1, NN )
+      END IF
+*
+      IF( .NOT.LSAME( JOB, 'N' ) .AND. .NOT.WANTS .AND. .NOT.WANTSP )
+     $     THEN
+         INFO = -1
+      ELSE IF( .NOT.LSAME( COMPQ, 'N' ) .AND. .NOT.WANTQ ) THEN
+         INFO = -2
+      ELSE IF( N.LT.0 ) THEN
+         INFO = -4
+      ELSE IF( LDT.LT.MAX( 1, N ) ) THEN
+         INFO = -6
+      ELSE IF( LDQ.LT.1 .OR. ( WANTQ .AND. LDQ.LT.N ) ) THEN
+         INFO = -8
+      ELSE IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
+         INFO = -14
+      END IF
+*
+      IF( INFO.EQ.0 ) THEN
+         WORK( 1 ) = LWMIN
+      END IF
+*
+      IF( INFO.NE.0 ) THEN
+         CALL XERBLA( 'ZTRSEN', -INFO )
+         RETURN
+      ELSE IF( LQUERY ) THEN
+         RETURN
+      END IF
+*
+*     Quick return if possible
+*
+      IF( M.EQ.N .OR. M.EQ.0 ) THEN
+         IF( WANTS )
+     $      S = ONE
+         IF( WANTSP )
+     $      SEP = ZLANGE( '1', N, N, T, LDT, RWORK )
+         GO TO 40
+      END IF
+*
+*     Collect the selected eigenvalues at the top left corner of T.
+*
+      KS = 0
+      DO 20 K = 1, N
+         IF( SELECT( K ) ) THEN
+            KS = KS + 1
+*
+*           Swap the K-th eigenvalue to position KS.
+*
+            IF( K.NE.KS )
+     $         CALL ZTREXC( COMPQ, N, T, LDT, Q, LDQ, K, KS, IERR )
+         END IF
+   20 CONTINUE
+*
+      IF( WANTS ) THEN
+*
+*        Solve the Sylvester equation for R:
+*
+*           T11*R - R*T22 = scale*T12
+*
+         CALL ZLACPY( 'F', N1, N2, T( 1, N1+1 ), LDT, WORK, N1 )
+         CALL ZTRSYL( 'N', 'N', -1, N1, N2, T, LDT, T( N1+1, N1+1 ),
+     $                LDT, WORK, N1, SCALE, IERR )
+*
+*        Estimate the reciprocal of the condition number of the cluster
+*        of eigenvalues.
+*
+         RNORM = ZLANGE( 'F', N1, N2, WORK, N1, RWORK )
+         IF( RNORM.EQ.ZERO ) THEN
+            S = ONE
+         ELSE
+            S = SCALE / ( SQRT( SCALE*SCALE / RNORM+RNORM )*
+     $          SQRT( RNORM ) )
+         END IF
+      END IF
+*
+      IF( WANTSP ) THEN
+*
+*        Estimate sep(T11,T22).
+*
+         EST = ZERO
+         KASE = 0
+   30    CONTINUE
+         CALL ZLACN2( NN, WORK( NN+1 ), WORK, EST, KASE, ISAVE )
+         IF( KASE.NE.0 ) THEN
+            IF( KASE.EQ.1 ) THEN
+*
+*              Solve T11*R - R*T22 = scale*X.
+*
+               CALL ZTRSYL( 'N', 'N', -1, N1, N2, T, LDT,
+     $                      T( N1+1, N1+1 ), LDT, WORK, N1, SCALE,
+     $                      IERR )
+            ELSE
+*
+*              Solve T11'*R - R*T22' = scale*X.
+*
+               CALL ZTRSYL( 'C', 'C', -1, N1, N2, T, LDT,
+     $                      T( N1+1, N1+1 ), LDT, WORK, N1, SCALE,
+     $                      IERR )
+            END IF
+            GO TO 30
+         END IF
+*
+         SEP = SCALE / EST
+      END IF
+*
+   40 CONTINUE
+*
+*     Copy reordered eigenvalues to W.
+*
+      DO 50 K = 1, N
+         W( K ) = T( K, K )
+   50 CONTINUE
+*
+      WORK( 1 ) = LWMIN
+*
+      RETURN
+*
+*     End of ZTRSEN
+*
+      END