dstebz.c

/* dstebz.f -- translated by f2c (version 20061008).
   You must link the resulting object file with libf2c:
	on Microsoft Windows system, link with libf2c.lib;
	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
	or, if you install libf2c.a in a standard place, with -lf2c -lm
	-- in that order, at the end of the command line, as in
		cc *.o -lf2c -lm
	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

		http://www.netlib.org/f2c/libf2c.zip
*/

#include "clapack.h"


/* Table of constant values */

static integer c__1 = 1;
static integer c_n1 = -1;
static integer c__3 = 3;
static integer c__2 = 2;
static integer c__0 = 0;

/* Subroutine */ int dstebz_(char *range, char *order, integer *n, doublereal 
	*vl, doublereal *vu, integer *il, integer *iu, doublereal *abstol, 
	doublereal *d__, doublereal *e, integer *m, integer *nsplit, 
	doublereal *w, integer *iblock, integer *isplit, doublereal *work, 
	integer *iwork, integer *info)
{
    /* System generated locals */
    integer i__1, i__2, i__3;
    doublereal d__1, d__2, d__3, d__4, d__5;

    /* Builtin functions */
    double sqrt(doublereal), log(doublereal);

    /* Local variables */
    integer j, ib, jb, ie, je, nb;
    doublereal gl;
    integer im, in;
    doublereal gu;
    integer iw;
    doublereal wl, wu;
    integer nwl;
    doublereal ulp, wlu, wul;
    integer nwu;
    doublereal tmp1, tmp2;
    integer iend, ioff, iout, itmp1, jdisc;
    extern logical lsame_(char *, char *);
    integer iinfo;
    doublereal atoli;
    integer iwoff;
    doublereal bnorm;
    integer itmax;
    doublereal wkill, rtoli, tnorm;
    extern doublereal dlamch_(char *);
    integer ibegin;
    extern /* Subroutine */ int dlaebz_(integer *, integer *, integer *, 
	    integer *, integer *, integer *, doublereal *, doublereal *, 
	    doublereal *, doublereal *, doublereal *, doublereal *, integer *, 
	     doublereal *, doublereal *, integer *, integer *, doublereal *, 
	    integer *, integer *);
    integer irange, idiscl;
    doublereal safemn;
    integer idumma[1];
    extern /* Subroutine */ int xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
	    integer *, integer *);
    integer idiscu, iorder;
    logical ncnvrg;
    doublereal pivmin;
    logical toofew;


/*  -- LAPACK routine (version 3.2) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */
/*     8-18-00:  Increase FUDGE factor for T3E (eca) */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DSTEBZ computes the eigenvalues of a symmetric tridiagonal */
/*  matrix T.  The user may ask for all eigenvalues, all eigenvalues */
/*  in the half-open interval (VL, VU], or the IL-th through IU-th */
/*  eigenvalues. */

/*  To avoid overflow, the matrix must be scaled so that its */
/*  largest element is no greater than overflow**(1/2) * */
/*  underflow**(1/4) in absolute value, and for greatest */
/*  accuracy, it should not be much smaller than that. */

/*  See W. Kahan "Accurate Eigenvalues of a Symmetric Tridiagonal */
/*  Matrix", Report CS41, Computer Science Dept., Stanford */
/*  University, July 21, 1966. */

/*  Arguments */
/*  ========= */

/*  RANGE   (input) CHARACTER*1 */
/*          = 'A': ("All")   all eigenvalues will be found. */
/*          = 'V': ("Value") all eigenvalues in the half-open interval */
/*                           (VL, VU] will be found. */
/*          = 'I': ("Index") the IL-th through IU-th eigenvalues (of the */
/*                           entire matrix) will be found. */

/*  ORDER   (input) CHARACTER*1 */
/*          = 'B': ("By Block") the eigenvalues will be grouped by */
/*                              split-off block (see IBLOCK, ISPLIT) and */
/*                              ordered from smallest to largest within */
/*                              the block. */
/*          = 'E': ("Entire matrix") */
/*                              the eigenvalues for the entire matrix */
/*                              will be ordered from smallest to */
/*                              largest. */

/*  N       (input) INTEGER */
/*          The order of the tridiagonal matrix T.  N >= 0. */

/*  VL      (input) DOUBLE PRECISION */
/*  VU      (input) DOUBLE PRECISION */
/*          If RANGE='V', the lower and upper bounds of the interval to */
/*          be searched for eigenvalues.  Eigenvalues less than or equal */
/*          to VL, or greater than VU, will not be returned.  VL < VU. */
/*          Not referenced if RANGE = 'A' or 'I'. */

/*  IL      (input) INTEGER */
/*  IU      (input) INTEGER */
/*          If RANGE='I', the indices (in ascending order) of the */
/*          smallest and largest eigenvalues to be returned. */
/*          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0. */
/*          Not referenced if RANGE = 'A' or 'V'. */

/*  ABSTOL  (input) DOUBLE PRECISION */
/*          The absolute tolerance for the eigenvalues.  An eigenvalue */
/*          (or cluster) is considered to be located if it has been */
/*          determined to lie in an interval whose width is ABSTOL or */
/*          less.  If ABSTOL is less than or equal to zero, then ULP*|T| */
/*          will be used, where |T| means the 1-norm of T. */

/*          Eigenvalues will be computed most accurately when ABSTOL is */
/*          set to twice the underflow threshold 2*DLAMCH('S'), not zero. */

/*  D       (input) DOUBLE PRECISION array, dimension (N) */
/*          The n diagonal elements of the tridiagonal matrix T. */

/*  E       (input) DOUBLE PRECISION array, dimension (N-1) */
/*          The (n-1) off-diagonal elements of the tridiagonal matrix T. */

/*  M       (output) INTEGER */
/*          The actual number of eigenvalues found. 0 <= M <= N. */
/*          (See also the description of INFO=2,3.) */

/*  NSPLIT  (output) INTEGER */
/*          The number of diagonal blocks in the matrix T. */
/*          1 <= NSPLIT <= N. */

/*  W       (output) DOUBLE PRECISION array, dimension (N) */
/*          On exit, the first M elements of W will contain the */
/*          eigenvalues.  (DSTEBZ may use the remaining N-M elements as */
/*          workspace.) */

/*  IBLOCK  (output) INTEGER array, dimension (N) */
/*          At each row/column j where E(j) is zero or small, the */
/*          matrix T is considered to split into a block diagonal */
/*          matrix.  On exit, if INFO = 0, IBLOCK(i) specifies to which */
/*          block (from 1 to the number of blocks) the eigenvalue W(i) */
/*          belongs.  (DSTEBZ may use the remaining N-M elements as */
/*          workspace.) */

/*  ISPLIT  (output) INTEGER array, dimension (N) */
/*          The splitting points, at which T breaks up into submatrices. */
/*          The first submatrix consists of rows/columns 1 to ISPLIT(1), */
/*          the second of rows/columns ISPLIT(1)+1 through ISPLIT(2), */
/*          etc., and the NSPLIT-th consists of rows/columns */
/*          ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N. */
/*          (Only the first NSPLIT elements will actually be used, but */
/*          since the user cannot know a priori what value NSPLIT will */
/*          have, N words must be reserved for ISPLIT.) */

/*  WORK    (workspace) DOUBLE PRECISION array, dimension (4*N) */

/*  IWORK   (workspace) INTEGER array, dimension (3*N) */

/*  INFO    (output) INTEGER */
/*          = 0:  successful exit */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value */
/*          > 0:  some or all of the eigenvalues failed to converge or */
/*                were not computed: */
/*                =1 or 3: Bisection failed to converge for some */
/*                        eigenvalues; these eigenvalues are flagged by a */
/*                        negative block number.  The effect is that the */
/*                        eigenvalues may not be as accurate as the */
/*                        absolute and relative tolerances.  This is */
/*                        generally caused by unexpectedly inaccurate */
/*                        arithmetic. */
/*                =2 or 3: RANGE='I' only: Not all of the eigenvalues */
/*                        IL:IU were found. */
/*                        Effect: M < IU+1-IL */
/*                        Cause:  non-monotonic arithmetic, causing the */
/*                                Sturm sequence to be non-monotonic. */
/*                        Cure:   recalculate, using RANGE='A', and pick */
/*                                out eigenvalues IL:IU.  In some cases, */
/*                                increasing the PARAMETER "FUDGE" may */
/*                                make things work. */
/*                = 4:    RANGE='I', and the Gershgorin interval */
/*                        initially used was too small.  No eigenvalues */
/*                        were computed. */
/*                        Probable cause: your machine has sloppy */
/*                                        floating-point arithmetic. */
/*                        Cure: Increase the PARAMETER "FUDGE", */
/*                              recompile, and try again. */

/*  Internal Parameters */
/*  =================== */

/*  RELFAC  DOUBLE PRECISION, default = 2.0e0 */
/*          The relative tolerance.  An interval (a,b] lies within */
/*          "relative tolerance" if  b-a < RELFAC*ulp*max(|a|,|b|), */
/*          where "ulp" is the machine precision (distance from 1 to */
/*          the next larger floating point number.) */

/*  FUDGE   DOUBLE PRECISION, default = 2 */
/*          A "fudge factor" to widen the Gershgorin intervals.  Ideally, */
/*          a value of 1 should work, but on machines with sloppy */
/*          arithmetic, this needs to be larger.  The default for */
/*          publicly released versions should be large enough to handle */
/*          the worst machine around.  Note that this has no effect */
/*          on accuracy of the solution. */

/*  ===================================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. Local Arrays .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

    /* Parameter adjustments */
    --iwork;
    --work;
    --isplit;
    --iblock;
    --w;
    --e;
    --d__;

    /* Function Body */
    *info = 0;

/*     Decode RANGE */

    if (lsame_(range, "A")) {
	irange = 1;
    } else if (lsame_(range, "V")) {
	irange = 2;
    } else if (lsame_(range, "I")) {
	irange = 3;
    } else {
	irange = 0;
    }

/*     Decode ORDER */

    if (lsame_(order, "B")) {
	iorder = 2;
    } else if (lsame_(order, "E")) {
	iorder = 1;
    } else {
	iorder = 0;
    }

/*     Check for Errors */

    if (irange <= 0) {
	*info = -1;
    } else if (iorder <= 0) {
	*info = -2;
    } else if (*n < 0) {
	*info = -3;
    } else if (irange == 2) {
	if (*vl >= *vu) {
	    *info = -5;
	}
    } else if (irange == 3 && (*il < 1 || *il > max(1,*n))) {
	*info = -6;
    } else if (irange == 3 && (*iu < min(*n,*il) || *iu > *n)) {
	*info = -7;
    }

    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DSTEBZ", &i__1);
	return 0;
    }

/*     Initialize error flags */

    *info = 0;
    ncnvrg = FALSE_;
    toofew = FALSE_;

/*     Quick return if possible */

    *m = 0;
    if (*n == 0) {
	return 0;
    }

/*     Simplifications: */

    if (irange == 3 && *il == 1 && *iu == *n) {
	irange = 1;
    }

/*     Get machine constants */
/*     NB is the minimum vector length for vector bisection, or 0 */
/*     if only scalar is to be done. */

    safemn = dlamch_("S");
    ulp = dlamch_("P");
    rtoli = ulp * 2.;
    nb = ilaenv_(&c__1, "DSTEBZ", " ", n, &c_n1, &c_n1, &c_n1);
    if (nb <= 1) {
	nb = 0;
    }

/*     Special Case when N=1 */

    if (*n == 1) {
	*nsplit = 1;
	isplit[1] = 1;
	if (irange == 2 && (*vl >= d__[1] || *vu < d__[1])) {
	    *m = 0;
	} else {
	    w[1] = d__[1];
	    iblock[1] = 1;
	    *m = 1;
	}
	return 0;
    }

/*     Compute Splitting Points */

    *nsplit = 1;
    work[*n] = 0.;
    pivmin = 1.;

/* DIR$ NOVECTOR */
    i__1 = *n;
    for (j = 2; j <= i__1; ++j) {
/* Computing 2nd power */
	d__1 = e[j - 1];
	tmp1 = d__1 * d__1;
/* Computing 2nd power */
	d__2 = ulp;
	if ((d__1 = d__[j] * d__[j - 1], abs(d__1)) * (d__2 * d__2) + safemn 
		> tmp1) {
	    isplit[*nsplit] = j - 1;
	    ++(*nsplit);
	    work[j - 1] = 0.;
	} else {
	    work[j - 1] = tmp1;
	    pivmin = max(pivmin,tmp1);
	}
/* L10: */
    }
    isplit[*nsplit] = *n;
    pivmin *= safemn;

/*     Compute Interval and ATOLI */

    if (irange == 3) {

/*        RANGE='I': Compute the interval containing eigenvalues */
/*                   IL through IU. */

/*        Compute Gershgorin interval for entire (split) matrix */
/*        and use it as the initial interval */

	gu = d__[1];
	gl = d__[1];
	tmp1 = 0.;

	i__1 = *n - 1;
	for (j = 1; j <= i__1; ++j) {
	    tmp2 = sqrt(work[j]);
/* Computing MAX */
	    d__1 = gu, d__2 = d__[j] + tmp1 + tmp2;
	    gu = max(d__1,d__2);
/* Computing MIN */
	    d__1 = gl, d__2 = d__[j] - tmp1 - tmp2;
	    gl = min(d__1,d__2);
	    tmp1 = tmp2;
/* L20: */
	}

/* Computing MAX */
	d__1 = gu, d__2 = d__[*n] + tmp1;
	gu = max(d__1,d__2);
/* Computing MIN */
	d__1 = gl, d__2 = d__[*n] - tmp1;
	gl = min(d__1,d__2);
/* Computing MAX */
	d__1 = abs(gl), d__2 = abs(gu);
	tnorm = max(d__1,d__2);
	gl = gl - tnorm * 2.1 * ulp * *n - pivmin * 4.2000000000000002;
	gu = gu + tnorm * 2.1 * ulp * *n + pivmin * 2.1;

/*        Compute Iteration parameters */

	itmax = (integer) ((log(tnorm + pivmin) - log(pivmin)) / log(2.)) + 2;
	if (*abstol <= 0.) {
	    atoli = ulp * tnorm;
	} else {
	    atoli = *abstol;
	}

	work[*n + 1] = gl;
	work[*n + 2] = gl;
	work[*n + 3] = gu;
	work[*n + 4] = gu;
	work[*n + 5] = gl;
	work[*n + 6] = gu;
	iwork[1] = -1;
	iwork[2] = -1;
	iwork[3] = *n + 1;
	iwork[4] = *n + 1;
	iwork[5] = *il - 1;
	iwork[6] = *iu;

	dlaebz_(&c__3, &itmax, n, &c__2, &c__2, &nb, &atoli, &rtoli, &pivmin, 
		&d__[1], &e[1], &work[1], &iwork[5], &work[*n + 1], &work[*n 
		+ 5], &iout, &iwork[1], &w[1], &iblock[1], &iinfo);

	if (iwork[6] == *iu) {
	    wl = work[*n + 1];
	    wlu = work[*n + 3];
	    nwl = iwork[1];
	    wu = work[*n + 4];
	    wul = work[*n + 2];
	    nwu = iwork[4];
	} else {
	    wl = work[*n + 2];
	    wlu = work[*n + 4];
	    nwl = iwork[2];
	    wu = work[*n + 3];
	    wul = work[*n + 1];
	    nwu = iwork[3];
	}

	if (nwl < 0 || nwl >= *n || nwu < 1 || nwu > *n) {
	    *info = 4;
	    return 0;
	}
    } else {

/*        RANGE='A' or 'V' -- Set ATOLI */

/* Computing MAX */
	d__3 = abs(d__[1]) + abs(e[1]), d__4 = (d__1 = d__[*n], abs(d__1)) + (
		d__2 = e[*n - 1], abs(d__2));
	tnorm = max(d__3,d__4);

	i__1 = *n - 1;
	for (j = 2; j <= i__1; ++j) {
/* Computing MAX */
	    d__4 = tnorm, d__5 = (d__1 = d__[j], abs(d__1)) + (d__2 = e[j - 1]
		    , abs(d__2)) + (d__3 = e[j], abs(d__3));
	    tnorm = max(d__4,d__5);
/* L30: */
	}

	if (*abstol <= 0.) {
	    atoli = ulp * tnorm;
	} else {
	    atoli = *abstol;
	}

	if (irange == 2) {
	    wl = *vl;
	    wu = *vu;
	} else {
	    wl = 0.;
	    wu = 0.;
	}
    }

/*     Find Eigenvalues -- Loop Over Blocks and recompute NWL and NWU. */
/*     NWL accumulates the number of eigenvalues .le. WL, */
/*     NWU accumulates the number of eigenvalues .le. WU */

    *m = 0;
    iend = 0;
    *info = 0;
    nwl = 0;
    nwu = 0;

    i__1 = *nsplit;
    for (jb = 1; jb <= i__1; ++jb) {
	ioff = iend;
	ibegin = ioff + 1;
	iend = isplit[jb];
	in = iend - ioff;

	if (in == 1) {

/*           Special Case -- IN=1 */

	    if (irange == 1 || wl >= d__[ibegin] - pivmin) {
		++nwl;
	    }
	    if (irange == 1 || wu >= d__[ibegin] - pivmin) {
		++nwu;
	    }
	    if (irange == 1 || wl < d__[ibegin] - pivmin && wu >= d__[ibegin] 
		    - pivmin) {
		++(*m);
		w[*m] = d__[ibegin];
		iblock[*m] = jb;
	    }
	} else {

/*           General Case -- IN > 1 */

/*           Compute Gershgorin Interval */
/*           and use it as the initial interval */

	    gu = d__[ibegin];
	    gl = d__[ibegin];
	    tmp1 = 0.;

	    i__2 = iend - 1;
	    for (j = ibegin; j <= i__2; ++j) {
		tmp2 = (d__1 = e[j], abs(d__1));
/* Computing MAX */
		d__1 = gu, d__2 = d__[j] + tmp1 + tmp2;
		gu = max(d__1,d__2);
/* Computing MIN */
		d__1 = gl, d__2 = d__[j] - tmp1 - tmp2;
		gl = min(d__1,d__2);
		tmp1 = tmp2;
/* L40: */
	    }

/* Computing MAX */
	    d__1 = gu, d__2 = d__[iend] + tmp1;
	    gu = max(d__1,d__2);
/* Computing MIN */
	    d__1 = gl, d__2 = d__[iend] - tmp1;
	    gl = min(d__1,d__2);
/* Computing MAX */
	    d__1 = abs(gl), d__2 = abs(gu);
	    bnorm = max(d__1,d__2);
	    gl = gl - bnorm * 2.1 * ulp * in - pivmin * 2.1;
	    gu = gu + bnorm * 2.1 * ulp * in + pivmin * 2.1;

/*           Compute ATOLI for the current submatrix */

	    if (*abstol <= 0.) {
/* Computing MAX */
		d__1 = abs(gl), d__2 = abs(gu);
		atoli = ulp * max(d__1,d__2);
	    } else {
		atoli = *abstol;
	    }

	    if (irange > 1) {
		if (gu < wl) {
		    nwl += in;
		    nwu += in;
		    goto L70;
		}
		gl = max(gl,wl);
		gu = min(gu,wu);
		if (gl >= gu) {
		    goto L70;
		}
	    }

/*           Set Up Initial Interval */

	    work[*n + 1] = gl;
	    work[*n + in + 1] = gu;
	    dlaebz_(&c__1, &c__0, &in, &in, &c__1, &nb, &atoli, &rtoli, &
		    pivmin, &d__[ibegin], &e[ibegin], &work[ibegin], idumma, &
		    work[*n + 1], &work[*n + (in << 1) + 1], &im, &iwork[1], &
		    w[*m + 1], &iblock[*m + 1], &iinfo);

	    nwl += iwork[1];
	    nwu += iwork[in + 1];
	    iwoff = *m - iwork[1];

/*           Compute Eigenvalues */

	    itmax = (integer) ((log(gu - gl + pivmin) - log(pivmin)) / log(2.)
		    ) + 2;
	    dlaebz_(&c__2, &itmax, &in, &in, &c__1, &nb, &atoli, &rtoli, &
		    pivmin, &d__[ibegin], &e[ibegin], &work[ibegin], idumma, &
		    work[*n + 1], &work[*n + (in << 1) + 1], &iout, &iwork[1], 
		     &w[*m + 1], &iblock[*m + 1], &iinfo);

/*           Copy Eigenvalues Into W and IBLOCK */
/*           Use -JB for block number for unconverged eigenvalues. */

	    i__2 = iout;
	    for (j = 1; j <= i__2; ++j) {
		tmp1 = (work[j + *n] + work[j + in + *n]) * .5;

/*              Flag non-convergence. */

		if (j > iout - iinfo) {
		    ncnvrg = TRUE_;
		    ib = -jb;
		} else {
		    ib = jb;
		}
		i__3 = iwork[j + in] + iwoff;
		for (je = iwork[j] + 1 + iwoff; je <= i__3; ++je) {
		    w[je] = tmp1;
		    iblock[je] = ib;
/* L50: */
		}
/* L60: */
	    }

	    *m += im;
	}
L70:
	;
    }

/*     If RANGE='I', then (WL,WU) contains eigenvalues NWL+1,...,NWU */
/*     If NWL+1 < IL or NWU > IU, discard extra eigenvalues. */

    if (irange == 3) {
	im = 0;
	idiscl = *il - 1 - nwl;
	idiscu = nwu - *iu;

	if (idiscl > 0 || idiscu > 0) {
	    i__1 = *m;
	    for (je = 1; je <= i__1; ++je) {
		if (w[je] <= wlu && idiscl > 0) {
		    --idiscl;
		} else if (w[je] >= wul && idiscu > 0) {
		    --idiscu;
		} else {
		    ++im;
		    w[im] = w[je];
		    iblock[im] = iblock[je];
		}
/* L80: */
	    }
	    *m = im;
	}
	if (idiscl > 0 || idiscu > 0) {

/*           Code to deal with effects of bad arithmetic: */
/*           Some low eigenvalues to be discarded are not in (WL,WLU], */
/*           or high eigenvalues to be discarded are not in (WUL,WU] */
/*           so just kill off the smallest IDISCL/largest IDISCU */
/*           eigenvalues, by simply finding the smallest/largest */
/*           eigenvalue(s). */

/*           (If N(w) is monotone non-decreasing, this should never */
/*               happen.) */

	    if (idiscl > 0) {
		wkill = wu;
		i__1 = idiscl;
		for (jdisc = 1; jdisc <= i__1; ++jdisc) {
		    iw = 0;
		    i__2 = *m;
		    for (je = 1; je <= i__2; ++je) {
			if (iblock[je] != 0 && (w[je] < wkill || iw == 0)) {
			    iw = je;
			    wkill = w[je];
			}
/* L90: */
		    }
		    iblock[iw] = 0;
/* L100: */
		}
	    }
	    if (idiscu > 0) {

		wkill = wl;
		i__1 = idiscu;
		for (jdisc = 1; jdisc <= i__1; ++jdisc) {
		    iw = 0;
		    i__2 = *m;
		    for (je = 1; je <= i__2; ++je) {
			if (iblock[je] != 0 && (w[je] > wkill || iw == 0)) {
			    iw = je;
			    wkill = w[je];
			}
/* L110: */
		    }
		    iblock[iw] = 0;
/* L120: */
		}
	    }
	    im = 0;
	    i__1 = *m;
	    for (je = 1; je <= i__1; ++je) {
		if (iblock[je] != 0) {
		    ++im;
		    w[im] = w[je];
		    iblock[im] = iblock[je];
		}
/* L130: */
	    }
	    *m = im;
	}
	if (idiscl < 0 || idiscu < 0) {
	    toofew = TRUE_;
	}
    }

/*     If ORDER='B', do nothing -- the eigenvalues are already sorted */
/*        by block. */
/*     If ORDER='E', sort the eigenvalues from smallest to largest */

    if (iorder == 1 && *nsplit > 1) {
	i__1 = *m - 1;
	for (je = 1; je <= i__1; ++je) {
	    ie = 0;
	    tmp1 = w[je];
	    i__2 = *m;
	    for (j = je + 1; j <= i__2; ++j) {
		if (w[j] < tmp1) {
		    ie = j;
		    tmp1 = w[j];
		}
/* L140: */
	    }

	    if (ie != 0) {
		itmp1 = iblock[ie];
		w[ie] = w[je];
		iblock[ie] = iblock[je];
		w[je] = tmp1;
		iblock[je] = itmp1;
	    }
/* L150: */
	}
    }

    *info = 0;
    if (ncnvrg) {
	++(*info);
    }
    if (toofew) {
	*info += 2;
    }
    return 0;

/*     End of DSTEBZ */

} /* dstebz_ */