text: #include "blaswrap.h"
  #include "f2c.h"
  
  /* Subroutine */ int stgsna_(char *job, char *howmny, logical *select, 
  	integer *n, real *a, integer *lda, real *b, integer *ldb, real *vl, 
  	integer *ldvl, real *vr, integer *ldvr, real *s, real *dif, integer *
  	mm, integer *m, real *work, integer *lwork, integer *iwork, integer *
  	info)
  {
  /*  -- LAPACK routine (version 3.0) --   
         Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
         Courant Institute, Argonne National Lab, and Rice University   
         June 30, 1999   
  
  
      Purpose   
      =======   
  
      STGSNA estimates reciprocal condition numbers for specified   
      eigenvalues and/or eigenvectors of a matrix pair (A, B) in   
      generalized real Schur canonical form (or of any matrix pair   
      (Q*A*Z', Q*B*Z') with orthogonal matrices Q and Z, where   
      Z' denotes the transpose of Z.   
  
      (A, B) must be in generalized real Schur 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.   
  
  
      Arguments   
      =========   
  
      JOB     (input) CHARACTER*1   
              Specifies whether condition numbers are required for   
              eigenvalues (S) or eigenvectors (DIF):   
              = 'E': for eigenvalues only (S);   
              = 'V': for eigenvectors only (DIF);   
              = 'B': for both eigenvalues and eigenvectors (S and DIF).   
  
      HOWMNY  (input) CHARACTER*1   
              = 'A': compute condition numbers for all eigenpairs;   
              = 'S': compute condition numbers for selected eigenpairs   
                     specified by the array SELECT.   
  
      SELECT  (input) LOGICAL array, dimension (N)   
              If HOWMNY = 'S', SELECT specifies the eigenpairs for which   
              condition numbers are required. To select condition numbers   
              for the eigenpair corresponding to a real eigenvalue w(j),   
              SELECT(j) must be set to .TRUE.. To select condition numbers   
              corresponding to a complex conjugate pair of eigenvalues w(j)   
              and w(j+1), either SELECT(j) or SELECT(j+1) or both, must be   
              set to .TRUE..   
              If HOWMNY = 'A', SELECT is not referenced.   
  
      N       (input) INTEGER   
              The order of the square matrix pair (A, B). N >= 0.   
  
      A       (input) REAL array, dimension (LDA,N)   
              The upper quasi-triangular matrix A in the pair (A,B).   
  
      LDA     (input) INTEGER   
              The leading dimension of the array A. LDA >= max(1,N).   
  
      B       (input) REAL array, dimension (LDB,N)   
              The upper triangular matrix B in the pair (A,B).   
  
      LDB     (input) INTEGER   
              The leading dimension of the array B. LDB >= max(1,N).   
  
      VL      (input) REAL array, dimension (LDVL,M)   
              If JOB = 'E' or 'B', VL must contain left eigenvectors of   
              (A, B), corresponding to the eigenpairs specified by HOWMNY   
              and SELECT. The eigenvectors must be stored in consecutive   
              columns of VL, as returned by STGEVC.   
              If JOB = 'V', VL is not referenced.   
  
      LDVL    (input) INTEGER   
              The leading dimension of the array VL. LDVL >= 1.   
              If JOB = 'E' or 'B', LDVL >= N.   
  
      VR      (input) REAL array, dimension (LDVR,M)   
              If JOB = 'E' or 'B', VR must contain right eigenvectors of   
              (A, B), corresponding to the eigenpairs specified by HOWMNY   
              and SELECT. The eigenvectors must be stored in consecutive   
              columns ov VR, as returned by STGEVC.   
              If JOB = 'V', VR is not referenced.   
  
      LDVR    (input) INTEGER   
              The leading dimension of the array VR. LDVR >= 1.   
              If JOB = 'E' or 'B', LDVR >= N.   
  
      S       (output) REAL array, dimension (MM)   
              If JOB = 'E' or 'B', the reciprocal condition numbers of the   
              selected eigenvalues, stored in consecutive elements of the   
              array. For a complex conjugate pair of eigenvalues two   
              consecutive elements of S are set to the same value. Thus   
              S(j), DIF(j), and the j-th columns of VL and VR all   
              correspond to the same eigenpair (but not in general the   
              j-th eigenpair, unless all eigenpairs are selected).   
              If JOB = 'V', S is not referenced.   
  
      DIF     (output) REAL array, dimension (MM)   
              If JOB = 'V' or 'B', the estimated reciprocal condition   
              numbers of the selected eigenvectors, stored in consecutive   
              elements of the array. For a complex eigenvector two   
              consecutive elements of DIF are set to the same value. If   
              the eigenvalues cannot be reordered to compute DIF(j), DIF(j)   
              is set to 0; this can only occur when the true value would be   
              very small anyway.   
              If JOB = 'E', DIF is not referenced.   
  
      MM      (input) INTEGER   
              The number of elements in the arrays S and DIF. MM >= M.   
  
      M       (output) INTEGER   
              The number of elements of the arrays S and DIF used to store   
              the specified condition numbers; for each selected real   
              eigenvalue one element is used, and for each selected complex   
              conjugate pair of eigenvalues, two elements are used.   
              If HOWMNY = 'A', M is set to N.   
  
      WORK    (workspace/output) REAL array, dimension (LWORK)   
              If JOB = 'E', 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 >= N.   
              If JOB = 'V' or 'B' LWORK >= 2*N*(N+2)+16.   
  
              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) INTEGER array, dimension (N + 6)   
              If JOB = 'E', IWORK is not referenced.   
  
      INFO    (output) INTEGER   
              =0: Successful exit   
              <0: If INFO = -i, the i-th argument had an illegal value   
  
  
      Further Details   
      ===============   
  
      The reciprocal of the condition number of a generalized eigenvalue   
      w = (a, b) is defined as   
  
           S(w) = (|u'Av|**2 + |u'Bv|**2)**(1/2) / (norm(u)*norm(v))   
  
      where u and v are the left and right eigenvectors of (A, B)   
      corresponding to w; |z| denotes the absolute value of the complex   
      number, and norm(u) denotes the 2-norm of the vector u.   
      The pair (a, b) corresponds to an eigenvalue w = a/b (= u'Av/u'Bv)   
      of the matrix pair (A, B). If both a and b equal zero, then (A B) is   
      singular and S(I) = -1 is returned.   
  
      An approximate error bound on the chordal distance between the i-th   
      computed generalized eigenvalue w and the corresponding exact   
      eigenvalue lambda is   
  
           chord(w, lambda) <= EPS * norm(A, B) / S(I)   
  
      where EPS is the machine precision.   
  
      The reciprocal of the condition number DIF(i) of right eigenvector u   
      and left eigenvector v corresponding to the generalized eigenvalue w   
      is defined as follows:   
  
      a) If the i-th eigenvalue w = (a,b) is real   
  
         Suppose U and V are orthogonal transformations such that   
  
                    U'*(A, B)*V  = (S, T) = ( a   *  ) ( b  *  )  1   
                                            ( 0  S22 ),( 0 T22 )  n-1   
                                              1  n-1     1 n-1   
  
         Then the reciprocal condition number DIF(i) is   
  
                    Difl((a, b), (S22, T22)) = sigma-min( Zl ),   
  
         where sigma-min(Zl) denotes the smallest singular value of the   
         2(n-1)-by-2(n-1) matrix   
  
             Zl = [ kron(a, In-1)  -kron(1, S22) ]   
                  [ kron(b, In-1)  -kron(1, T22) ] .   
  
         Here In-1 is the identity matrix of size n-1. kron(X, Y) is the   
         Kronecker product between the matrices X and Y.   
  
         Note that if the default method for computing DIF(i) is wanted   
         (see SLATDF), then the parameter DIFDRI (see below) should be   
         changed from 3 to 4 (routine SLATDF(IJOB = 2 will be used)).   
         See STGSYL for more details.   
  
      b) If the i-th and (i+1)-th eigenvalues are complex conjugate pair,   
  
         Suppose U and V are orthogonal transformations such that   
  
                    U'*(A, B)*V = (S, T) = ( S11  *   ) ( T11  *  )  2   
                                           ( 0    S22 ),( 0    T22) n-2   
                                             2    n-2     2    n-2   
  
         and (S11, T11) corresponds to the complex conjugate eigenvalue   
         pair (w, conjg(w)). There exist unitary matrices U1 and V1 such   
         that   
  
             U1'*S11*V1 = ( s11 s12 )   and U1'*T11*V1 = ( t11 t12 )   
                          (  0  s22 )                    (  0  t22 )   
  
         where the generalized eigenvalues w = s11/t11 and   
         conjg(w) = s22/t22.   
  
         Then the reciprocal condition number DIF(i) is bounded by   
  
             min( d1, max( 1, |real(s11)/real(s22)| )*d2 )   
  
         where, d1 = Difl((s11, t11), (s22, t22)) = sigma-min(Z1), where   
         Z1 is the complex 2-by-2 matrix   
  
                  Z1 =  [ s11  -s22 ]   
                        [ t11  -t22 ],   
  
         This is done by computing (using real arithmetic) the   
         roots of the characteristical polynomial det(Z1' * Z1 - lambda I),   
         where Z1' denotes the conjugate transpose of Z1 and det(X) denotes   
         the determinant of X.   
  
         and d2 is an upper bound on Difl((S11, T11), (S22, T22)), i.e. an   
         upper bound on sigma-min(Z2), where Z2 is (2n-2)-by-(2n-2)   
  
                  Z2 = [ kron(S11', In-2)  -kron(I2, S22) ]   
                       [ kron(T11', In-2)  -kron(I2, T22) ]   
  
         Note that if the default method for computing DIF is wanted (see   
         SLATDF), then the parameter DIFDRI (see below) should be changed   
         from 3 to 4 (routine SLATDF(IJOB = 2 will be used)). See STGSYL   
         for more details.   
  
      For each eigenvalue/vector specified by SELECT, DIF stores a   
      Frobenius norm-based estimate of Difl.   
  
      An approximate error bound for the i-th computed eigenvector VL(i) or   
      VR(i) is given by   
  
                 EPS * norm(A, B) / DIF(i).   
  
      See ref. [2-3] for more details and further references.   
  
      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.   
  
      =====================================================================   
  
  
         Decode and test the input parameters   
  
         Parameter adjustments */
      /* Table of constant values */
      static integer c__1 = 1;
      static real c_b19 = 1.f;
      static real c_b21 = 0.f;
      static integer c__2 = 2;
      static logical c_false = FALSE_;
      static integer c__3 = 3;
      
      /* System generated locals */
      integer a_dim1, a_offset, b_dim1, b_offset, vl_dim1, vl_offset, vr_dim1, 
  	    vr_offset, i__1, i__2;
      real r__1, r__2;
      /* Builtin functions */
      double sqrt(doublereal);
      /* Local variables */
      static real beta, cond;
      static logical pair;
      static integer ierr;
      static real uhav, uhbv;
      static integer ifst;
      static real lnrm;
      extern doublereal sdot_(integer *, real *, integer *, real *, integer *);
      static integer ilst;
      static real rnrm;
      extern /* Subroutine */ int slag2_(real *, integer *, real *, integer *, 
  	    real *, real *, real *, real *, real *, real *);
      extern doublereal snrm2_(integer *, real *, integer *);
      static real root1, root2;
      static integer i__, k;
      static real scale;
      extern logical lsame_(char *, char *);
      static real uhavi, uhbvi;
      extern /* Subroutine */ int sgemv_(char *, integer *, integer *, real *, 
  	    real *, integer *, real *, integer *, real *, real *, integer *);
      static real tmpii, c1, c2;
      static integer lwmin;
      static logical wants;
      static real tmpir;
      static integer n1, n2;
      static real tmpri, dummy[1], tmprr;
      extern doublereal slapy2_(real *, real *);
      static real dummy1[1];
      static integer ks;
      static real alphai;
      static integer iz;
      static real alphar;
      extern doublereal slamch_(char *);
      extern /* Subroutine */ int xerbla_(char *, integer *);
      static logical wantbh, wantdf;
      extern /* Subroutine */ int slacpy_(char *, integer *, integer *, real *, 
  	    integer *, real *, integer *), stgexc_(logical *, logical 
  	    *, integer *, real *, integer *, real *, integer *, real *, 
  	    integer *, real *, integer *, integer *, integer *, real *, 
  	    integer *, integer *);
      static logical somcon;
      static real alprqt, smlnum;
      static logical lquery;
      extern /* Subroutine */ int stgsyl_(char *, integer *, integer *, integer 
  	    *, real *, integer *, real *, integer *, real *, integer *, real *
  	    , integer *, real *, integer *, real *, integer *, real *, real *,
  	     real *, integer *, integer *, integer *);
      static real eps;
  #define a_ref(a_1,a_2) a[(a_2)*a_dim1 + a_1]
  #define b_ref(a_1,a_2) b[(a_2)*b_dim1 + a_1]
  #define vl_ref(a_1,a_2) vl[(a_2)*vl_dim1 + a_1]
  #define vr_ref(a_1,a_2) vr[(a_2)*vr_dim1 + a_1]
  
  
      --select;
      a_dim1 = *lda;
      a_offset = 1 + a_dim1 * 1;
      a -= a_offset;
      b_dim1 = *ldb;
      b_offset = 1 + b_dim1 * 1;
      b -= b_offset;
      vl_dim1 = *ldvl;
      vl_offset = 1 + vl_dim1 * 1;
      vl -= vl_offset;
      vr_dim1 = *ldvr;
      vr_offset = 1 + vr_dim1 * 1;
      vr -= vr_offset;
      --s;
      --dif;
      --work;
      --iwork;
  
      /* Function Body */
      wantbh = lsame_(job, "B");
      wants = lsame_(job, "E") || wantbh;
      wantdf = lsame_(job, "V") || wantbh;
  
      somcon = lsame_(howmny, "S");
  
      *info = 0;
      lquery = *lwork == -1;
  
      if (lsame_(job, "V") || lsame_(job, "B")) {
  /* Computing MAX */
  	i__1 = 1, i__2 = (*n << 1) * (*n + 2) + 16;
  	lwmin = max(i__1,i__2);
      } else {
  	lwmin = 1;
      }
  
      if (! wants && ! wantdf) {
  	*info = -1;
      } else if (! lsame_(howmny, "A") && ! somcon) {
  	*info = -2;
      } else if (*n < 0) {
  	*info = -4;
      } else if (*lda < max(1,*n)) {
  	*info = -6;
      } else if (*ldb < max(1,*n)) {
  	*info = -8;
      } else if (wants && *ldvl < *n) {
  	*info = -10;
      } else if (wants && *ldvr < *n) {
  	*info = -12;
      } else {
  
  /*        Set M to the number of eigenpairs for which condition numbers   
            are required, and test MM. */
  
  	if (somcon) {
  	    *m = 0;
  	    pair = FALSE_;
  	    i__1 = *n;
  	    for (k = 1; k <= i__1; ++k) {
  		if (pair) {
  		    pair = FALSE_;
  		} else {
  		    if (k < *n) {
  			if (a_ref(k + 1, k) == 0.f) {
  			    if (select[k]) {
  				++(*m);
  			    }
  			} else {
  			    pair = TRUE_;
  			    if (select[k] || select[k + 1]) {
  				*m += 2;
  			    }
  			}
  		    } else {
  			if (select[*n]) {
  			    ++(*m);
  			}
  		    }
  		}
  /* L10: */
  	    }
  	} else {
  	    *m = *n;
  	}
  
  	if (*mm < *m) {
  	    *info = -15;
  	} else if (*lwork < lwmin && ! lquery) {
  	    *info = -18;
  /*        ELSE IF( WANTDF .AND. LWORK.LT.2*N*( N+2 )+16 ) THEN   
               INFO = -18 */
  	}
      }
  
      if (*info == 0) {
  	work[1] = (real) lwmin;
      }
  
      if (*info != 0) {
  	i__1 = -(*info);
  	xerbla_("STGSNA", &i__1);
  	return 0;
      } else if (lquery) {
  	return 0;
      }
  
  /*     Quick return if possible */
  
      if (*n == 0) {
  	return 0;
      }
  
  /*     Get machine constants */
  
      eps = slamch_("P");
      smlnum = slamch_("S") / eps;
      ks = 0;
      pair = FALSE_;
  
      i__1 = *n;
      for (k = 1; k <= i__1; ++k) {
  
  /*        Determine whether A(k,k) begins a 1-by-1 or 2-by-2 block. */
  
  	if (pair) {
  	    pair = FALSE_;
  	    goto L20;
  	} else {
  	    if (k < *n) {
  		pair = a_ref(k + 1, k) != 0.f;
  	    }
  	}
  
  /*        Determine whether condition numbers are required for the k-th   
            eigenpair. */
  
  	if (somcon) {
  	    if (pair) {
  		if (! select[k] && ! select[k + 1]) {
  		    goto L20;
  		}
  	    } else {
  		if (! select[k]) {
  		    goto L20;
  		}
  	    }
  	}
  
  	++ks;
  
  	if (wants) {
  
  /*           Compute the reciprocal condition number of the k-th   
               eigenvalue. */
  
  	    if (pair) {
  
  /*              Complex eigenvalue pair. */
  
  		r__1 = snrm2_(n, &vr_ref(1, ks), &c__1);
  		r__2 = snrm2_(n, &vr_ref(1, ks + 1), &c__1);
  		rnrm = slapy2_(&r__1, &r__2);
  		r__1 = snrm2_(n, &vl_ref(1, ks), &c__1);
  		r__2 = snrm2_(n, &vl_ref(1, ks + 1), &c__1);
  		lnrm = slapy2_(&r__1, &r__2);
  		sgemv_("N", n, n, &c_b19, &a[a_offset], lda, &vr_ref(1, ks), &
  			c__1, &c_b21, &work[1], &c__1);
  		tmprr = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		tmpri = sdot_(n, &work[1], &c__1, &vl_ref(1, ks + 1), &c__1);
  		sgemv_("N", n, n, &c_b19, &a[a_offset], lda, &vr_ref(1, ks + 
  			1), &c__1, &c_b21, &work[1], &c__1);
  		tmpii = sdot_(n, &work[1], &c__1, &vl_ref(1, ks + 1), &c__1);
  		tmpir = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		uhav = tmprr + tmpii;
  		uhavi = tmpir - tmpri;
  		sgemv_("N", n, n, &c_b19, &b[b_offset], ldb, &vr_ref(1, ks), &
  			c__1, &c_b21, &work[1], &c__1);
  		tmprr = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		tmpri = sdot_(n, &work[1], &c__1, &vl_ref(1, ks + 1), &c__1);
  		sgemv_("N", n, n, &c_b19, &b[b_offset], ldb, &vr_ref(1, ks + 
  			1), &c__1, &c_b21, &work[1], &c__1);
  		tmpii = sdot_(n, &work[1], &c__1, &vl_ref(1, ks + 1), &c__1);
  		tmpir = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		uhbv = tmprr + tmpii;
  		uhbvi = tmpir - tmpri;
  		uhav = slapy2_(&uhav, &uhavi);
  		uhbv = slapy2_(&uhbv, &uhbvi);
  		cond = slapy2_(&uhav, &uhbv);
  		s[ks] = cond / (rnrm * lnrm);
  		s[ks + 1] = s[ks];
  
  	    } else {
  
  /*              Real eigenvalue. */
  
  		rnrm = snrm2_(n, &vr_ref(1, ks), &c__1);
  		lnrm = snrm2_(n, &vl_ref(1, ks), &c__1);
  		sgemv_("N", n, n, &c_b19, &a[a_offset], lda, &vr_ref(1, ks), &
  			c__1, &c_b21, &work[1], &c__1);
  		uhav = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		sgemv_("N", n, n, &c_b19, &b[b_offset], ldb, &vr_ref(1, ks), &
  			c__1, &c_b21, &work[1], &c__1);
  		uhbv = sdot_(n, &work[1], &c__1, &vl_ref(1, ks), &c__1);
  		cond = slapy2_(&uhav, &uhbv);
  		if (cond == 0.f) {
  		    s[ks] = -1.f;
  		} else {
  		    s[ks] = cond / (rnrm * lnrm);
  		}
  	    }
  	}
  
  	if (wantdf) {
  	    if (*n == 1) {
  		dif[ks] = slapy2_(&a_ref(1, 1), &b_ref(1, 1));
  		goto L20;
  	    }
  
  /*           Estimate the reciprocal condition number of the k-th   
               eigenvectors. */
  	    if (pair) {
  
  /*              Copy the  2-by 2 pencil beginning at (A(k,k), B(k, k)).   
                  Compute the eigenvalue(s) at position K. */
  
  		work[1] = a_ref(k, k);
  		work[2] = a_ref(k + 1, k);
  		work[3] = a_ref(k, k + 1);
  		work[4] = a_ref(k + 1, k + 1);
  		work[5] = b_ref(k, k);
  		work[6] = b_ref(k + 1, k);
  		work[7] = b_ref(k, k + 1);
  		work[8] = b_ref(k + 1, k + 1);
  		r__1 = smlnum * eps;
  		slag2_(&work[1], &c__2, &work[5], &c__2, &r__1, &beta, dummy1,
  			 &alphar, dummy, &alphai);
  		alprqt = 1.f;
  		c1 = (alphar * alphar + alphai * alphai + beta * beta) * 2.f;
  		c2 = beta * 4.f * beta * alphai * alphai;
  		root1 = c1 + sqrt(c1 * c1 - c2 * 4.f);
  		root2 = c2 / root1;
  		root1 /= 2.f;
  /* Computing MIN */
  		r__1 = sqrt(root1), r__2 = sqrt(root2);
  		cond = dmin(r__1,r__2);
  	    }
  
  /*           Copy the matrix (A, B) to the array WORK and swap the   
               diagonal block beginning at A(k,k) to the (1,1) position. */
  
  	    slacpy_("Full", n, n, &a[a_offset], lda, &work[1], n);
  	    slacpy_("Full", n, n, &b[b_offset], ldb, &work[*n * *n + 1], n);
  	    ifst = k;
  	    ilst = 1;
  
  	    i__2 = *lwork - (*n << 1) * *n;
  	    stgexc_(&c_false, &c_false, n, &work[1], n, &work[*n * *n + 1], n,
  		     dummy, &c__1, dummy1, &c__1, &ifst, &ilst, &work[(*n * *
  		    n << 1) + 1], &i__2, &ierr);
  
  	    if (ierr > 0) {
  
  /*              Ill-conditioned problem - swap rejected. */
  
  		dif[ks] = 0.f;
  	    } else {
  
  /*              Reordering successful, solve generalized Sylvester   
                  equation for R and L,   
                             A22 * R - L * A11 = A12   
                             B22 * R - L * B11 = B12,   
                  and compute estimate of Difl((A11,B11), (A22, B22)). */
  
  		n1 = 1;
  		if (work[2] != 0.f) {
  		    n1 = 2;
  		}
  		n2 = *n - n1;
  		if (n2 == 0) {
  		    dif[ks] = cond;
  		} else {
  		    i__ = *n * *n + 1;
  		    iz = (*n << 1) * *n + 1;
  		    i__2 = *lwork - (*n << 1) * *n;
  		    stgsyl_("N", &c__3, &n2, &n1, &work[*n * n1 + n1 + 1], n, 
  			    &work[1], n, &work[n1 + 1], n, &work[*n * n1 + n1 
  			    + i__], n, &work[i__], n, &work[n1 + i__], n, &
  			    scale, &dif[ks], &work[iz + 1], &i__2, &iwork[1], 
  			    &ierr);
  
  		    if (pair) {
  /* Computing MIN */
  			r__1 = dmax(1.f,alprqt) * dif[ks];
  			dif[ks] = dmin(r__1,cond);
  		    }
  		}
  	    }
  	    if (pair) {
  		dif[ks + 1] = dif[ks];
  	    }
  	}
  	if (pair) {
  	    ++ks;
  	}
  
  L20:
  	;
      }
      work[1] = (real) lwmin;
      return 0;
  
  /*     End of STGSNA */
  
  } /* stgsna_ */
  
  #undef vr_ref
  #undef vl_ref
  #undef b_ref
  #undef a_ref
  
  
  