text: #include "f2c.h"
  #include "blaswrap.h"
  
  /* Table of constant values */
  
  static logical c_false = FALSE_;
  static integer c__1 = 1;
  static doublereal c_b22 = 1.;
  static doublereal c_b25 = 0.;
  static integer c__2 = 2;
  static logical c_true = TRUE_;
  
  /* Subroutine */ int dtrevc_(char *side, char *howmny, logical *select, 
  	integer *n, doublereal *t, integer *ldt, doublereal *vl, integer *
  	ldvl, doublereal *vr, integer *ldvr, integer *mm, integer *m, 
  	doublereal *work, integer *info)
  {
      /* System generated locals */
      integer t_dim1, t_offset, vl_dim1, vl_offset, vr_dim1, vr_offset, i__1, 
  	    i__2, i__3;
      doublereal d__1, d__2, d__3, d__4;
  
      /* Builtin functions */
      double sqrt(doublereal);
  
      /* Local variables */
      integer i__, j, k;
      doublereal x[4]	/* was [2][2] */;
      integer j1, j2, n2, ii, ki, ip, is;
      doublereal wi, wr, rec, ulp, beta, emax;
      logical pair;
      extern doublereal ddot_(integer *, doublereal *, integer *, doublereal *, 
  	    integer *);
      logical allv;
      integer ierr;
      doublereal unfl, ovfl, smin;
      logical over;
      doublereal vmax;
      integer jnxt;
      extern /* Subroutine */ int dscal_(integer *, doublereal *, doublereal *, 
  	    integer *);
      doublereal scale;
      extern logical lsame_(char *, char *);
      extern /* Subroutine */ int dgemv_(char *, integer *, integer *, 
  	    doublereal *, doublereal *, integer *, doublereal *, integer *, 
  	    doublereal *, doublereal *, integer *);
      doublereal remax;
      extern /* Subroutine */ int dcopy_(integer *, doublereal *, integer *, 
  	    doublereal *, integer *);
      logical leftv, bothv;
      extern /* Subroutine */ int daxpy_(integer *, doublereal *, doublereal *, 
  	    integer *, doublereal *, integer *);
      doublereal vcrit;
      logical somev;
      doublereal xnorm;
      extern /* Subroutine */ int dlaln2_(logical *, integer *, integer *, 
  	    doublereal *, doublereal *, doublereal *, integer *, doublereal *, 
  	     doublereal *, doublereal *, integer *, doublereal *, doublereal *
  , doublereal *, integer *, doublereal *, doublereal *, integer *),
  	     dlabad_(doublereal *, doublereal *);
      extern doublereal dlamch_(char *);
      extern integer idamax_(integer *, doublereal *, integer *);
      extern /* Subroutine */ int xerbla_(char *, integer *);
      doublereal bignum;
      logical rightv;
      doublereal smlnum;
  
  
  /*  -- LAPACK routine (version 3.1) -- */
  /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
  /*     November 2006 */
  
  /*     .. Scalar Arguments .. */
  /*     .. */
  /*     .. Array Arguments .. */
  /*     .. */
  
  /*  Purpose */
  /*  ======= */
  
  /*  DTREVC computes some or all of the right and/or left eigenvectors of */
  /*  a real upper quasi-triangular matrix T. */
  /*  Matrices of this type are produced by the Schur factorization of */
  /*  a real general matrix:  A = Q*T*Q**T, as computed by DHSEQR. */
  
  /*  The right eigenvector x and the left eigenvector y of T corresponding */
  /*  to an eigenvalue w are defined by: */
  
  /*     T*x = w*x,     (y**H)*T = w*(y**H) */
  
  /*  where y**H denotes the conjugate transpose of y. */
  /*  The eigenvalues are not input to this routine, but are read directly */
  /*  from the diagonal blocks of T. */
  
  /*  This routine returns the matrices X and/or Y of right and left */
  /*  eigenvectors of T, or the products Q*X and/or Q*Y, where Q is an */
  /*  input matrix.  If Q is the orthogonal factor that reduces a matrix */
  /*  A to Schur form T, then Q*X and Q*Y are the matrices of right and */
  /*  left eigenvectors of A. */
  
  /*  Arguments */
  /*  ========= */
  
  /*  SIDE    (input) CHARACTER*1 */
  /*          = 'R':  compute right eigenvectors only; */
  /*          = 'L':  compute left eigenvectors only; */
  /*          = 'B':  compute both right and left eigenvectors. */
  
  /*  HOWMNY  (input) CHARACTER*1 */
  /*          = 'A':  compute all right and/or left eigenvectors; */
  /*          = 'B':  compute all right and/or left eigenvectors, */
  /*                  backtransformed by the matrices in VR and/or VL; */
  /*          = 'S':  compute selected right and/or left eigenvectors, */
  /*                  as indicated by the logical array SELECT. */
  
  /*  SELECT  (input/output) LOGICAL array, dimension (N) */
  /*          If HOWMNY = 'S', SELECT specifies the eigenvectors to be */
  /*          computed. */
  /*          If w(j) is a real eigenvalue, the corresponding real */
  /*          eigenvector is computed if SELECT(j) is .TRUE.. */
  /*          If w(j) and w(j+1) are the real and imaginary parts of a */
  /*          complex eigenvalue, the corresponding complex eigenvector is */
  /*          computed if either SELECT(j) or SELECT(j+1) is .TRUE., and */
  /*          on exit SELECT(j) is set to .TRUE. and SELECT(j+1) is set to */
  /*          .FALSE.. */
  /*          Not referenced if HOWMNY = 'A' or 'B'. */
  
  /*  N       (input) INTEGER */
  /*          The order of the matrix T. N >= 0. */
  
  /*  T       (input) DOUBLE PRECISION array, dimension (LDT,N) */
  /*          The upper quasi-triangular matrix T in Schur canonical form. */
  
  /*  LDT     (input) INTEGER */
  /*          The leading dimension of the array T. LDT >= max(1,N). */
  
  /*  VL      (input/output) DOUBLE PRECISION array, dimension (LDVL,MM) */
  /*          On entry, if SIDE = 'L' or 'B' and HOWMNY = 'B', VL must */
  /*          contain an N-by-N matrix Q (usually the orthogonal matrix Q */
  /*          of Schur vectors returned by DHSEQR). */
  /*          On exit, if SIDE = 'L' or 'B', VL contains: */
  /*          if HOWMNY = 'A', the matrix Y of left eigenvectors of T; */
  /*          if HOWMNY = 'B', the matrix Q*Y; */
  /*          if HOWMNY = 'S', the left eigenvectors of T specified by */
  /*                           SELECT, stored consecutively in the columns */
  /*                           of VL, in the same order as their */
  /*                           eigenvalues. */
  /*          A complex eigenvector corresponding to a complex eigenvalue */
  /*          is stored in two consecutive columns, the first holding the */
  /*          real part, and the second the imaginary part. */
  /*          Not referenced if SIDE = 'R'. */
  
  /*  LDVL    (input) INTEGER */
  /*          The leading dimension of the array VL.  LDVL >= 1, and if */
  /*          SIDE = 'L' or 'B', LDVL >= N. */
  
  /*  VR      (input/output) DOUBLE PRECISION array, dimension (LDVR,MM) */
  /*          On entry, if SIDE = 'R' or 'B' and HOWMNY = 'B', VR must */
  /*          contain an N-by-N matrix Q (usually the orthogonal matrix Q */
  /*          of Schur vectors returned by DHSEQR). */
  /*          On exit, if SIDE = 'R' or 'B', VR contains: */
  /*          if HOWMNY = 'A', the matrix X of right eigenvectors of T; */
  /*          if HOWMNY = 'B', the matrix Q*X; */
  /*          if HOWMNY = 'S', the right eigenvectors of T specified by */
  /*                           SELECT, stored consecutively in the columns */
  /*                           of VR, in the same order as their */
  /*                           eigenvalues. */
  /*          A complex eigenvector corresponding to a complex eigenvalue */
  /*          is stored in two consecutive columns, the first holding the */
  /*          real part and the second the imaginary part. */
  /*          Not referenced if SIDE = 'L'. */
  
  /*  LDVR    (input) INTEGER */
  /*          The leading dimension of the array VR.  LDVR >= 1, and if */
  /*          SIDE = 'R' or 'B', LDVR >= N. */
  
  /*  MM      (input) INTEGER */
  /*          The number of columns in the arrays VL and/or VR. MM >= M. */
  
  /*  M       (output) INTEGER */
  /*          The number of columns in the arrays VL and/or VR actually */
  /*          used to store the eigenvectors. */
  /*          If HOWMNY = 'A' or 'B', M is set to N. */
  /*          Each selected real eigenvector occupies one column and each */
  /*          selected complex eigenvector occupies two columns. */
  
  /*  WORK    (workspace) DOUBLE PRECISION array, dimension (3*N) */
  
  /*  INFO    (output) INTEGER */
  /*          = 0:  successful exit */
  /*          < 0:  if INFO = -i, the i-th argument had an illegal value */
  
  /*  Further Details */
  /*  =============== */
  
  /*  The algorithm used in this program is basically backward (forward) */
  /*  substitution, with scaling to make the the code robust against */
  /*  possible overflow. */
  
  /*  Each eigenvector is normalized so that the element of largest */
  /*  magnitude has magnitude 1; here the magnitude of a complex number */
  /*  (x,y) is taken to be |x| + |y|. */
  
  /*  ===================================================================== */
  
  /*     .. Parameters .. */
  /*     .. */
  /*     .. Local Scalars .. */
  /*     .. */
  /*     .. External Functions .. */
  /*     .. */
  /*     .. External Subroutines .. */
  /*     .. */
  /*     .. Intrinsic Functions .. */
  /*     .. */
  /*     .. Local Arrays .. */
  /*     .. */
  /*     .. Executable Statements .. */
  
  /*     Decode and test the input parameters */
  
      /* Parameter adjustments */
      --select;
      t_dim1 = *ldt;
      t_offset = 1 + t_dim1;
      t -= t_offset;
      vl_dim1 = *ldvl;
      vl_offset = 1 + vl_dim1;
      vl -= vl_offset;
      vr_dim1 = *ldvr;
      vr_offset = 1 + vr_dim1;
      vr -= vr_offset;
      --work;
  
      /* Function Body */
      bothv = lsame_(side, "B");
      rightv = lsame_(side, "R") || bothv;
      leftv = lsame_(side, "L") || bothv;
  
      allv = lsame_(howmny, "A");
      over = lsame_(howmny, "B");
      somev = lsame_(howmny, "S");
  
      *info = 0;
      if (! rightv && ! leftv) {
  	*info = -1;
      } else if (! allv && ! over && ! somev) {
  	*info = -2;
      } else if (*n < 0) {
  	*info = -4;
      } else if (*ldt < max(1,*n)) {
  	*info = -6;
      } else if (*ldvl < 1 || leftv && *ldvl < *n) {
  	*info = -8;
      } else if (*ldvr < 1 || rightv && *ldvr < *n) {
  	*info = -10;
      } else {
  
  /*        Set M to the number of columns required to store the selected */
  /*        eigenvectors, standardize the array SELECT if necessary, and */
  /*        test MM. */
  
  	if (somev) {
  	    *m = 0;
  	    pair = FALSE_;
  	    i__1 = *n;
  	    for (j = 1; j <= i__1; ++j) {
  		if (pair) {
  		    pair = FALSE_;
  		    select[j] = FALSE_;
  		} else {
  		    if (j < *n) {
  			if (t[j + 1 + j * t_dim1] == 0.) {
  			    if (select[j]) {
  				++(*m);
  			    }
  			} else {
  			    pair = TRUE_;
  			    if (select[j] || select[j + 1]) {
  				select[j] = TRUE_;
  				*m += 2;
  			    }
  			}
  		    } else {
  			if (select[*n]) {
  			    ++(*m);
  			}
  		    }
  		}
  /* L10: */
  	    }
  	} else {
  	    *m = *n;
  	}
  
  	if (*mm < *m) {
  	    *info = -11;
  	}
      }
      if (*info != 0) {
  	i__1 = -(*info);
  	xerbla_("DTREVC", &i__1);
  	return 0;
      }
  
  /*     Quick return if possible. */
  
      if (*n == 0) {
  	return 0;
      }
  
  /*     Set the constants to control overflow. */
  
      unfl = dlamch_("Safe minimum");
      ovfl = 1. / unfl;
      dlabad_(&unfl, &ovfl);
      ulp = dlamch_("Precision");
      smlnum = unfl * (*n / ulp);
      bignum = (1. - ulp) / smlnum;
  
  /*     Compute 1-norm of each column of strictly upper triangular */
  /*     part of T to control overflow in triangular solver. */
  
      work[1] = 0.;
      i__1 = *n;
      for (j = 2; j <= i__1; ++j) {
  	work[j] = 0.;
  	i__2 = j - 1;
  	for (i__ = 1; i__ <= i__2; ++i__) {
  	    work[j] += (d__1 = t[i__ + j * t_dim1], abs(d__1));
  /* L20: */
  	}
  /* L30: */
      }
  
  /*     Index IP is used to specify the real or complex eigenvalue: */
  /*       IP = 0, real eigenvalue, */
  /*            1, first of conjugate complex pair: (wr,wi) */
  /*           -1, second of conjugate complex pair: (wr,wi) */
  
      n2 = *n << 1;
  
      if (rightv) {
  
  /*        Compute right eigenvectors. */
  
  	ip = 0;
  	is = *m;
  	for (ki = *n; ki >= 1; --ki) {
  
  	    if (ip == 1) {
  		goto L130;
  	    }
  	    if (ki == 1) {
  		goto L40;
  	    }
  	    if (t[ki + (ki - 1) * t_dim1] == 0.) {
  		goto L40;
  	    }
  	    ip = -1;
  
  L40:
  	    if (somev) {
  		if (ip == 0) {
  		    if (! select[ki]) {
  			goto L130;
  		    }
  		} else {
  		    if (! select[ki - 1]) {
  			goto L130;
  		    }
  		}
  	    }
  
  /*           Compute the KI-th eigenvalue (WR,WI). */
  
  	    wr = t[ki + ki * t_dim1];
  	    wi = 0.;
  	    if (ip != 0) {
  		wi = sqrt((d__1 = t[ki + (ki - 1) * t_dim1], abs(d__1))) * 
  			sqrt((d__2 = t[ki - 1 + ki * t_dim1], abs(d__2)));
  	    }
  /* Computing MAX */
  	    d__1 = ulp * (abs(wr) + abs(wi));
  	    smin = max(d__1,smlnum);
  
  	    if (ip == 0) {
  
  /*              Real right eigenvector */
  
  		work[ki + *n] = 1.;
  
  /*              Form right-hand side */
  
  		i__1 = ki - 1;
  		for (k = 1; k <= i__1; ++k) {
  		    work[k + *n] = -t[k + ki * t_dim1];
  /* L50: */
  		}
  
  /*              Solve the upper quasi-triangular system: */
  /*                 (T(1:KI-1,1:KI-1) - WR)*X = SCALE*WORK. */
  
  		jnxt = ki - 1;
  		for (j = ki - 1; j >= 1; --j) {
  		    if (j > jnxt) {
  			goto L60;
  		    }
  		    j1 = j;
  		    j2 = j;
  		    jnxt = j - 1;
  		    if (j > 1) {
  			if (t[j + (j - 1) * t_dim1] != 0.) {
  			    j1 = j - 1;
  			    jnxt = j - 2;
  			}
  		    }
  
  		    if (j1 == j2) {
  
  /*                    1-by-1 diagonal block */
  
  			dlaln2_(&c_false, &c__1, &c__1, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &c_b25, x, &c__2, &scale, &xnorm, 
  				&ierr);
  
  /*                    Scale X(1,1) to avoid overflow when updating */
  /*                    the right-hand side. */
  
  			if (xnorm > 1.) {
  			    if (work[j] > bignum / xnorm) {
  				x[0] /= xnorm;
  				scale /= xnorm;
  			    }
  			}
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    dscal_(&ki, &scale, &work[*n + 1], &c__1);
  			}
  			work[j + *n] = x[0];
  
  /*                    Update right-hand side */
  
  			i__1 = j - 1;
  			d__1 = -x[0];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				*n + 1], &c__1);
  
  		    } else {
  
  /*                    2-by-2 diagonal block */
  
  			dlaln2_(&c_false, &c__2, &c__1, &smin, &c_b22, &t[j - 
  				1 + (j - 1) * t_dim1], ldt, &c_b22, &c_b22, &
  				work[j - 1 + *n], n, &wr, &c_b25, x, &c__2, &
  				scale, &xnorm, &ierr);
  
  /*                    Scale X(1,1) and X(2,1) to avoid overflow when */
  /*                    updating the right-hand side. */
  
  			if (xnorm > 1.) {
  /* Computing MAX */
  			    d__1 = work[j - 1], d__2 = work[j];
  			    beta = max(d__1,d__2);
  			    if (beta > bignum / xnorm) {
  				x[0] /= xnorm;
  				x[1] /= xnorm;
  				scale /= xnorm;
  			    }
  			}
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    dscal_(&ki, &scale, &work[*n + 1], &c__1);
  			}
  			work[j - 1 + *n] = x[0];
  			work[j + *n] = x[1];
  
  /*                    Update right-hand side */
  
  			i__1 = j - 2;
  			d__1 = -x[0];
  			daxpy_(&i__1, &d__1, &t[(j - 1) * t_dim1 + 1], &c__1, 
  				&work[*n + 1], &c__1);
  			i__1 = j - 2;
  			d__1 = -x[1];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				*n + 1], &c__1);
  		    }
  L60:
  		    ;
  		}
  
  /*              Copy the vector x or Q*x to VR and normalize. */
  
  		if (! over) {
  		    dcopy_(&ki, &work[*n + 1], &c__1, &vr[is * vr_dim1 + 1], &
  			    c__1);
  
  		    ii = idamax_(&ki, &vr[is * vr_dim1 + 1], &c__1);
  		    remax = 1. / (d__1 = vr[ii + is * vr_dim1], abs(d__1));
  		    dscal_(&ki, &remax, &vr[is * vr_dim1 + 1], &c__1);
  
  		    i__1 = *n;
  		    for (k = ki + 1; k <= i__1; ++k) {
  			vr[k + is * vr_dim1] = 0.;
  /* L70: */
  		    }
  		} else {
  		    if (ki > 1) {
  			i__1 = ki - 1;
  			dgemv_("N", n, &i__1, &c_b22, &vr[vr_offset], ldvr, &
  				work[*n + 1], &c__1, &work[ki + *n], &vr[ki * 
  				vr_dim1 + 1], &c__1);
  		    }
  
  		    ii = idamax_(n, &vr[ki * vr_dim1 + 1], &c__1);
  		    remax = 1. / (d__1 = vr[ii + ki * vr_dim1], abs(d__1));
  		    dscal_(n, &remax, &vr[ki * vr_dim1 + 1], &c__1);
  		}
  
  	    } else {
  
  /*              Complex right eigenvector. */
  
  /*              Initial solve */
  /*                [ (T(KI-1,KI-1) T(KI-1,KI) ) - (WR + I* WI)]*X = 0. */
  /*                [ (T(KI,KI-1)   T(KI,KI)   )               ] */
  
  		if ((d__1 = t[ki - 1 + ki * t_dim1], abs(d__1)) >= (d__2 = t[
  			ki + (ki - 1) * t_dim1], abs(d__2))) {
  		    work[ki - 1 + *n] = 1.;
  		    work[ki + n2] = wi / t[ki - 1 + ki * t_dim1];
  		} else {
  		    work[ki - 1 + *n] = -wi / t[ki + (ki - 1) * t_dim1];
  		    work[ki + n2] = 1.;
  		}
  		work[ki + *n] = 0.;
  		work[ki - 1 + n2] = 0.;
  
  /*              Form right-hand side */
  
  		i__1 = ki - 2;
  		for (k = 1; k <= i__1; ++k) {
  		    work[k + *n] = -work[ki - 1 + *n] * t[k + (ki - 1) * 
  			    t_dim1];
  		    work[k + n2] = -work[ki + n2] * t[k + ki * t_dim1];
  /* L80: */
  		}
  
  /*              Solve upper quasi-triangular system: */
  /*              (T(1:KI-2,1:KI-2) - (WR+i*WI))*X = SCALE*(WORK+i*WORK2) */
  
  		jnxt = ki - 2;
  		for (j = ki - 2; j >= 1; --j) {
  		    if (j > jnxt) {
  			goto L90;
  		    }
  		    j1 = j;
  		    j2 = j;
  		    jnxt = j - 1;
  		    if (j > 1) {
  			if (t[j + (j - 1) * t_dim1] != 0.) {
  			    j1 = j - 1;
  			    jnxt = j - 2;
  			}
  		    }
  
  		    if (j1 == j2) {
  
  /*                    1-by-1 diagonal block */
  
  			dlaln2_(&c_false, &c__1, &c__2, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &wi, x, &c__2, &scale, &xnorm, &
  				ierr);
  
  /*                    Scale X(1,1) and X(1,2) to avoid overflow when */
  /*                    updating the right-hand side. */
  
  			if (xnorm > 1.) {
  			    if (work[j] > bignum / xnorm) {
  				x[0] /= xnorm;
  				x[2] /= xnorm;
  				scale /= xnorm;
  			    }
  			}
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    dscal_(&ki, &scale, &work[*n + 1], &c__1);
  			    dscal_(&ki, &scale, &work[n2 + 1], &c__1);
  			}
  			work[j + *n] = x[0];
  			work[j + n2] = x[2];
  
  /*                    Update the right-hand side */
  
  			i__1 = j - 1;
  			d__1 = -x[0];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				*n + 1], &c__1);
  			i__1 = j - 1;
  			d__1 = -x[2];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				n2 + 1], &c__1);
  
  		    } else {
  
  /*                    2-by-2 diagonal block */
  
  			dlaln2_(&c_false, &c__2, &c__2, &smin, &c_b22, &t[j - 
  				1 + (j - 1) * t_dim1], ldt, &c_b22, &c_b22, &
  				work[j - 1 + *n], n, &wr, &wi, x, &c__2, &
  				scale, &xnorm, &ierr);
  
  /*                    Scale X to avoid overflow when updating */
  /*                    the right-hand side. */
  
  			if (xnorm > 1.) {
  /* Computing MAX */
  			    d__1 = work[j - 1], d__2 = work[j];
  			    beta = max(d__1,d__2);
  			    if (beta > bignum / xnorm) {
  				rec = 1. / xnorm;
  				x[0] *= rec;
  				x[2] *= rec;
  				x[1] *= rec;
  				x[3] *= rec;
  				scale *= rec;
  			    }
  			}
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    dscal_(&ki, &scale, &work[*n + 1], &c__1);
  			    dscal_(&ki, &scale, &work[n2 + 1], &c__1);
  			}
  			work[j - 1 + *n] = x[0];
  			work[j + *n] = x[1];
  			work[j - 1 + n2] = x[2];
  			work[j + n2] = x[3];
  
  /*                    Update the right-hand side */
  
  			i__1 = j - 2;
  			d__1 = -x[0];
  			daxpy_(&i__1, &d__1, &t[(j - 1) * t_dim1 + 1], &c__1, 
  				&work[*n + 1], &c__1);
  			i__1 = j - 2;
  			d__1 = -x[1];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				*n + 1], &c__1);
  			i__1 = j - 2;
  			d__1 = -x[2];
  			daxpy_(&i__1, &d__1, &t[(j - 1) * t_dim1 + 1], &c__1, 
  				&work[n2 + 1], &c__1);
  			i__1 = j - 2;
  			d__1 = -x[3];
  			daxpy_(&i__1, &d__1, &t[j * t_dim1 + 1], &c__1, &work[
  				n2 + 1], &c__1);
  		    }
  L90:
  		    ;
  		}
  
  /*              Copy the vector x or Q*x to VR and normalize. */
  
  		if (! over) {
  		    dcopy_(&ki, &work[*n + 1], &c__1, &vr[(is - 1) * vr_dim1 
  			    + 1], &c__1);
  		    dcopy_(&ki, &work[n2 + 1], &c__1, &vr[is * vr_dim1 + 1], &
  			    c__1);
  
  		    emax = 0.;
  		    i__1 = ki;
  		    for (k = 1; k <= i__1; ++k) {
  /* Computing MAX */
  			d__3 = emax, d__4 = (d__1 = vr[k + (is - 1) * vr_dim1]
  				, abs(d__1)) + (d__2 = vr[k + is * vr_dim1], 
  				abs(d__2));
  			emax = max(d__3,d__4);
  /* L100: */
  		    }
  
  		    remax = 1. / emax;
  		    dscal_(&ki, &remax, &vr[(is - 1) * vr_dim1 + 1], &c__1);
  		    dscal_(&ki, &remax, &vr[is * vr_dim1 + 1], &c__1);
  
  		    i__1 = *n;
  		    for (k = ki + 1; k <= i__1; ++k) {
  			vr[k + (is - 1) * vr_dim1] = 0.;
  			vr[k + is * vr_dim1] = 0.;
  /* L110: */
  		    }
  
  		} else {
  
  		    if (ki > 2) {
  			i__1 = ki - 2;
  			dgemv_("N", n, &i__1, &c_b22, &vr[vr_offset], ldvr, &
  				work[*n + 1], &c__1, &work[ki - 1 + *n], &vr[(
  				ki - 1) * vr_dim1 + 1], &c__1);
  			i__1 = ki - 2;
  			dgemv_("N", n, &i__1, &c_b22, &vr[vr_offset], ldvr, &
  				work[n2 + 1], &c__1, &work[ki + n2], &vr[ki * 
  				vr_dim1 + 1], &c__1);
  		    } else {
  			dscal_(n, &work[ki - 1 + *n], &vr[(ki - 1) * vr_dim1 
  				+ 1], &c__1);
  			dscal_(n, &work[ki + n2], &vr[ki * vr_dim1 + 1], &
  				c__1);
  		    }
  
  		    emax = 0.;
  		    i__1 = *n;
  		    for (k = 1; k <= i__1; ++k) {
  /* Computing MAX */
  			d__3 = emax, d__4 = (d__1 = vr[k + (ki - 1) * vr_dim1]
  				, abs(d__1)) + (d__2 = vr[k + ki * vr_dim1], 
  				abs(d__2));
  			emax = max(d__3,d__4);
  /* L120: */
  		    }
  		    remax = 1. / emax;
  		    dscal_(n, &remax, &vr[(ki - 1) * vr_dim1 + 1], &c__1);
  		    dscal_(n, &remax, &vr[ki * vr_dim1 + 1], &c__1);
  		}
  	    }
  
  	    --is;
  	    if (ip != 0) {
  		--is;
  	    }
  L130:
  	    if (ip == 1) {
  		ip = 0;
  	    }
  	    if (ip == -1) {
  		ip = 1;
  	    }
  /* L140: */
  	}
      }
  
      if (leftv) {
  
  /*        Compute left eigenvectors. */
  
  	ip = 0;
  	is = 1;
  	i__1 = *n;
  	for (ki = 1; ki <= i__1; ++ki) {
  
  	    if (ip == -1) {
  		goto L250;
  	    }
  	    if (ki == *n) {
  		goto L150;
  	    }
  	    if (t[ki + 1 + ki * t_dim1] == 0.) {
  		goto L150;
  	    }
  	    ip = 1;
  
  L150:
  	    if (somev) {
  		if (! select[ki]) {
  		    goto L250;
  		}
  	    }
  
  /*           Compute the KI-th eigenvalue (WR,WI). */
  
  	    wr = t[ki + ki * t_dim1];
  	    wi = 0.;
  	    if (ip != 0) {
  		wi = sqrt((d__1 = t[ki + (ki + 1) * t_dim1], abs(d__1))) * 
  			sqrt((d__2 = t[ki + 1 + ki * t_dim1], abs(d__2)));
  	    }
  /* Computing MAX */
  	    d__1 = ulp * (abs(wr) + abs(wi));
  	    smin = max(d__1,smlnum);
  
  	    if (ip == 0) {
  
  /*              Real left eigenvector. */
  
  		work[ki + *n] = 1.;
  
  /*              Form right-hand side */
  
  		i__2 = *n;
  		for (k = ki + 1; k <= i__2; ++k) {
  		    work[k + *n] = -t[ki + k * t_dim1];
  /* L160: */
  		}
  
  /*              Solve the quasi-triangular system: */
  /*                 (T(KI+1:N,KI+1:N) - WR)'*X = SCALE*WORK */
  
  		vmax = 1.;
  		vcrit = bignum;
  
  		jnxt = ki + 1;
  		i__2 = *n;
  		for (j = ki + 1; j <= i__2; ++j) {
  		    if (j < jnxt) {
  			goto L170;
  		    }
  		    j1 = j;
  		    j2 = j;
  		    jnxt = j + 1;
  		    if (j < *n) {
  			if (t[j + 1 + j * t_dim1] != 0.) {
  			    j2 = j + 1;
  			    jnxt = j + 2;
  			}
  		    }
  
  		    if (j1 == j2) {
  
  /*                    1-by-1 diagonal block */
  
  /*                    Scale if necessary to avoid overflow when forming */
  /*                    the right-hand side. */
  
  			if (work[j] > vcrit) {
  			    rec = 1. / vmax;
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + *n], &c__1);
  			    vmax = 1.;
  			    vcrit = bignum;
  			}
  
  			i__3 = j - ki - 1;
  			work[j + *n] -= ddot_(&i__3, &t[ki + 1 + j * t_dim1], 
  				&c__1, &work[ki + 1 + *n], &c__1);
  
  /*                    Solve (T(J,J)-WR)'*X = WORK */
  
  			dlaln2_(&c_false, &c__1, &c__1, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &c_b25, x, &c__2, &scale, &xnorm, 
  				&ierr);
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + *n], &c__1);
  			}
  			work[j + *n] = x[0];
  /* Computing MAX */
  			d__2 = (d__1 = work[j + *n], abs(d__1));
  			vmax = max(d__2,vmax);
  			vcrit = bignum / vmax;
  
  		    } else {
  
  /*                    2-by-2 diagonal block */
  
  /*                    Scale if necessary to avoid overflow when forming */
  /*                    the right-hand side. */
  
  /* Computing MAX */
  			d__1 = work[j], d__2 = work[j + 1];
  			beta = max(d__1,d__2);
  			if (beta > vcrit) {
  			    rec = 1. / vmax;
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + *n], &c__1);
  			    vmax = 1.;
  			    vcrit = bignum;
  			}
  
  			i__3 = j - ki - 1;
  			work[j + *n] -= ddot_(&i__3, &t[ki + 1 + j * t_dim1], 
  				&c__1, &work[ki + 1 + *n], &c__1);
  
  			i__3 = j - ki - 1;
  			work[j + 1 + *n] -= ddot_(&i__3, &t[ki + 1 + (j + 1) *
  				 t_dim1], &c__1, &work[ki + 1 + *n], &c__1);
  
  /*                    Solve */
  /*                      [T(J,J)-WR   T(J,J+1)     ]'* X = SCALE*( WORK1 ) */
  /*                      [T(J+1,J)    T(J+1,J+1)-WR]             ( WORK2 ) */
  
  			dlaln2_(&c_true, &c__2, &c__1, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &c_b25, x, &c__2, &scale, &xnorm, 
  				&ierr);
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + *n], &c__1);
  			}
  			work[j + *n] = x[0];
  			work[j + 1 + *n] = x[1];
  
  /* Computing MAX */
  			d__3 = (d__1 = work[j + *n], abs(d__1)), d__4 = (d__2 
  				= work[j + 1 + *n], abs(d__2)), d__3 = max(
  				d__3,d__4);
  			vmax = max(d__3,vmax);
  			vcrit = bignum / vmax;
  
  		    }
  L170:
  		    ;
  		}
  
  /*              Copy the vector x or Q*x to VL and normalize. */
  
  		if (! over) {
  		    i__2 = *n - ki + 1;
  		    dcopy_(&i__2, &work[ki + *n], &c__1, &vl[ki + is * 
  			    vl_dim1], &c__1);
  
  		    i__2 = *n - ki + 1;
  		    ii = idamax_(&i__2, &vl[ki + is * vl_dim1], &c__1) + ki - 
  			    1;
  		    remax = 1. / (d__1 = vl[ii + is * vl_dim1], abs(d__1));
  		    i__2 = *n - ki + 1;
  		    dscal_(&i__2, &remax, &vl[ki + is * vl_dim1], &c__1);
  
  		    i__2 = ki - 1;
  		    for (k = 1; k <= i__2; ++k) {
  			vl[k + is * vl_dim1] = 0.;
  /* L180: */
  		    }
  
  		} else {
  
  		    if (ki < *n) {
  			i__2 = *n - ki;
  			dgemv_("N", n, &i__2, &c_b22, &vl[(ki + 1) * vl_dim1 
  				+ 1], ldvl, &work[ki + 1 + *n], &c__1, &work[
  				ki + *n], &vl[ki * vl_dim1 + 1], &c__1);
  		    }
  
  		    ii = idamax_(n, &vl[ki * vl_dim1 + 1], &c__1);
  		    remax = 1. / (d__1 = vl[ii + ki * vl_dim1], abs(d__1));
  		    dscal_(n, &remax, &vl[ki * vl_dim1 + 1], &c__1);
  
  		}
  
  	    } else {
  
  /*              Complex left eigenvector. */
  
  /*               Initial solve: */
  /*                 ((T(KI,KI)    T(KI,KI+1) )' - (WR - I* WI))*X = 0. */
  /*                 ((T(KI+1,KI) T(KI+1,KI+1))                ) */
  
  		if ((d__1 = t[ki + (ki + 1) * t_dim1], abs(d__1)) >= (d__2 = 
  			t[ki + 1 + ki * t_dim1], abs(d__2))) {
  		    work[ki + *n] = wi / t[ki + (ki + 1) * t_dim1];
  		    work[ki + 1 + n2] = 1.;
  		} else {
  		    work[ki + *n] = 1.;
  		    work[ki + 1 + n2] = -wi / t[ki + 1 + ki * t_dim1];
  		}
  		work[ki + 1 + *n] = 0.;
  		work[ki + n2] = 0.;
  
  /*              Form right-hand side */
  
  		i__2 = *n;
  		for (k = ki + 2; k <= i__2; ++k) {
  		    work[k + *n] = -work[ki + *n] * t[ki + k * t_dim1];
  		    work[k + n2] = -work[ki + 1 + n2] * t[ki + 1 + k * t_dim1]
  			    ;
  /* L190: */
  		}
  
  /*              Solve complex quasi-triangular system: */
  /*              ( T(KI+2,N:KI+2,N) - (WR-i*WI) )*X = WORK1+i*WORK2 */
  
  		vmax = 1.;
  		vcrit = bignum;
  
  		jnxt = ki + 2;
  		i__2 = *n;
  		for (j = ki + 2; j <= i__2; ++j) {
  		    if (j < jnxt) {
  			goto L200;
  		    }
  		    j1 = j;
  		    j2 = j;
  		    jnxt = j + 1;
  		    if (j < *n) {
  			if (t[j + 1 + j * t_dim1] != 0.) {
  			    j2 = j + 1;
  			    jnxt = j + 2;
  			}
  		    }
  
  		    if (j1 == j2) {
  
  /*                    1-by-1 diagonal block */
  
  /*                    Scale if necessary to avoid overflow when */
  /*                    forming the right-hand side elements. */
  
  			if (work[j] > vcrit) {
  			    rec = 1. / vmax;
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + *n], &c__1);
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + n2], &c__1);
  			    vmax = 1.;
  			    vcrit = bignum;
  			}
  
  			i__3 = j - ki - 2;
  			work[j + *n] -= ddot_(&i__3, &t[ki + 2 + j * t_dim1], 
  				&c__1, &work[ki + 2 + *n], &c__1);
  			i__3 = j - ki - 2;
  			work[j + n2] -= ddot_(&i__3, &t[ki + 2 + j * t_dim1], 
  				&c__1, &work[ki + 2 + n2], &c__1);
  
  /*                    Solve (T(J,J)-(WR-i*WI))*(X11+i*X12)= WK+I*WK2 */
  
  			d__1 = -wi;
  			dlaln2_(&c_false, &c__1, &c__2, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &d__1, x, &c__2, &scale, &xnorm, &
  				ierr);
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + *n], &c__1);
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + n2], &c__1);
  			}
  			work[j + *n] = x[0];
  			work[j + n2] = x[2];
  /* Computing MAX */
  			d__3 = (d__1 = work[j + *n], abs(d__1)), d__4 = (d__2 
  				= work[j + n2], abs(d__2)), d__3 = max(d__3,
  				d__4);
  			vmax = max(d__3,vmax);
  			vcrit = bignum / vmax;
  
  		    } else {
  
  /*                    2-by-2 diagonal block */
  
  /*                    Scale if necessary to avoid overflow when forming */
  /*                    the right-hand side elements. */
  
  /* Computing MAX */
  			d__1 = work[j], d__2 = work[j + 1];
  			beta = max(d__1,d__2);
  			if (beta > vcrit) {
  			    rec = 1. / vmax;
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + *n], &c__1);
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &rec, &work[ki + n2], &c__1);
  			    vmax = 1.;
  			    vcrit = bignum;
  			}
  
  			i__3 = j - ki - 2;
  			work[j + *n] -= ddot_(&i__3, &t[ki + 2 + j * t_dim1], 
  				&c__1, &work[ki + 2 + *n], &c__1);
  
  			i__3 = j - ki - 2;
  			work[j + n2] -= ddot_(&i__3, &t[ki + 2 + j * t_dim1], 
  				&c__1, &work[ki + 2 + n2], &c__1);
  
  			i__3 = j - ki - 2;
  			work[j + 1 + *n] -= ddot_(&i__3, &t[ki + 2 + (j + 1) *
  				 t_dim1], &c__1, &work[ki + 2 + *n], &c__1);
  
  			i__3 = j - ki - 2;
  			work[j + 1 + n2] -= ddot_(&i__3, &t[ki + 2 + (j + 1) *
  				 t_dim1], &c__1, &work[ki + 2 + n2], &c__1);
  
  /*                    Solve 2-by-2 complex linear equation */
  /*                      ([T(j,j)   T(j,j+1)  ]'-(wr-i*wi)*I)*X = SCALE*B */
  /*                      ([T(j+1,j) T(j+1,j+1)]             ) */
  
  			d__1 = -wi;
  			dlaln2_(&c_true, &c__2, &c__2, &smin, &c_b22, &t[j + 
  				j * t_dim1], ldt, &c_b22, &c_b22, &work[j + *
  				n], n, &wr, &d__1, x, &c__2, &scale, &xnorm, &
  				ierr);
  
  /*                    Scale if necessary */
  
  			if (scale != 1.) {
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + *n], &c__1);
  			    i__3 = *n - ki + 1;
  			    dscal_(&i__3, &scale, &work[ki + n2], &c__1);
  			}
  			work[j + *n] = x[0];
  			work[j + n2] = x[2];
  			work[j + 1 + *n] = x[1];
  			work[j + 1 + n2] = x[3];
  /* Computing MAX */
  			d__1 = abs(x[0]), d__2 = abs(x[2]), d__1 = max(d__1,
  				d__2), d__2 = abs(x[1]), d__1 = max(d__1,d__2)
  				, d__2 = abs(x[3]), d__1 = max(d__1,d__2);
  			vmax = max(d__1,vmax);
  			vcrit = bignum / vmax;
  
  		    }
  L200:
  		    ;
  		}
  
  /*              Copy the vector x or Q*x to VL and normalize. */
  
  		if (! over) {
  		    i__2 = *n - ki + 1;
  		    dcopy_(&i__2, &work[ki + *n], &c__1, &vl[ki + is * 
  			    vl_dim1], &c__1);
  		    i__2 = *n - ki + 1;
  		    dcopy_(&i__2, &work[ki + n2], &c__1, &vl[ki + (is + 1) * 
  			    vl_dim1], &c__1);
  
  		    emax = 0.;
  		    i__2 = *n;
  		    for (k = ki; k <= i__2; ++k) {
  /* Computing MAX */
  			d__3 = emax, d__4 = (d__1 = vl[k + is * vl_dim1], abs(
  				d__1)) + (d__2 = vl[k + (is + 1) * vl_dim1], 
  				abs(d__2));
  			emax = max(d__3,d__4);
  /* L220: */
  		    }
  		    remax = 1. / emax;
  		    i__2 = *n - ki + 1;
  		    dscal_(&i__2, &remax, &vl[ki + is * vl_dim1], &c__1);
  		    i__2 = *n - ki + 1;
  		    dscal_(&i__2, &remax, &vl[ki + (is + 1) * vl_dim1], &c__1)
  			    ;
  
  		    i__2 = ki - 1;
  		    for (k = 1; k <= i__2; ++k) {
  			vl[k + is * vl_dim1] = 0.;
  			vl[k + (is + 1) * vl_dim1] = 0.;
  /* L230: */
  		    }
  		} else {
  		    if (ki < *n - 1) {
  			i__2 = *n - ki - 1;
  			dgemv_("N", n, &i__2, &c_b22, &vl[(ki + 2) * vl_dim1 
  				+ 1], ldvl, &work[ki + 2 + *n], &c__1, &work[
  				ki + *n], &vl[ki * vl_dim1 + 1], &c__1);
  			i__2 = *n - ki - 1;
  			dgemv_("N", n, &i__2, &c_b22, &vl[(ki + 2) * vl_dim1 
  				+ 1], ldvl, &work[ki + 2 + n2], &c__1, &work[
  				ki + 1 + n2], &vl[(ki + 1) * vl_dim1 + 1], &
  				c__1);
  		    } else {
  			dscal_(n, &work[ki + *n], &vl[ki * vl_dim1 + 1], &
  				c__1);
  			dscal_(n, &work[ki + 1 + n2], &vl[(ki + 1) * vl_dim1 
  				+ 1], &c__1);
  		    }
  
  		    emax = 0.;
  		    i__2 = *n;
  		    for (k = 1; k <= i__2; ++k) {
  /* Computing MAX */
  			d__3 = emax, d__4 = (d__1 = vl[k + ki * vl_dim1], abs(
  				d__1)) + (d__2 = vl[k + (ki + 1) * vl_dim1], 
  				abs(d__2));
  			emax = max(d__3,d__4);
  /* L240: */
  		    }
  		    remax = 1. / emax;
  		    dscal_(n, &remax, &vl[ki * vl_dim1 + 1], &c__1);
  		    dscal_(n, &remax, &vl[(ki + 1) * vl_dim1 + 1], &c__1);
  
  		}
  
  	    }
  
  	    ++is;
  	    if (ip != 0) {
  		++is;
  	    }
  L250:
  	    if (ip == -1) {
  		ip = 0;
  	    }
  	    if (ip == 1) {
  		ip = -1;
  	    }
  
  /* L260: */
  	}
  
      }
  
      return 0;
  
  /*     End of DTREVC */
  
  } /* dtrevc_ */
  