#include "clapack.h"
/* Table of constant values */
static integer c__1 = 1;
/* Subroutine */ int dlarrf_(integer *n, doublereal *d__, doublereal *l,
doublereal *ld, integer *clstrt, integer *clend, doublereal *w,
doublereal *wgap, doublereal *werr, doublereal *spdiam, doublereal *
clgapl, doublereal *clgapr, doublereal *pivmin, doublereal *sigma,
doublereal *dplus, doublereal *lplus, doublereal *work, integer *info)
{
/* System generated locals */
integer i__1;
doublereal d__1, d__2, d__3;
/* Builtin functions */
double sqrt(doublereal);
/* Local variables */
integer i__;
doublereal s, bestshift, smlgrowth, eps, tmp, max1, max2, rrr1, rrr2,
znm2, growthbound, fail, fact, oldp;
integer indx;
doublereal prod;
integer ktry;
doublereal fail2, avgap, ldmax, rdmax;
integer shift;
extern /* Subroutine */ int dcopy_(integer *, doublereal *, integer *,
doublereal *, integer *);
logical dorrr1;
extern doublereal dlamch_(char *);
doublereal ldelta;
logical nofail;
doublereal mingap, lsigma, rdelta;
extern logical disnan_(doublereal *);
logical forcer;
doublereal rsigma, clwdth;
logical sawnan1, sawnan2, tryrrr1;
/* -- LAPACK auxiliary routine (version 3.1) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* * */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* Given the initial representation L D L^T and its cluster of close */
/* eigenvalues (in a relative measure), W( CLSTRT ), W( CLSTRT+1 ), ... */
/* W( CLEND ), DLARRF finds a new relatively robust representation */
/* L D L^T - SIGMA I = L(+) D(+) L(+)^T such that at least one of the */
/* eigenvalues of L(+) D(+) L(+)^T is relatively isolated. */
/* Arguments */
/* ========= */
/* N (input) INTEGER */
/* The order of the matrix (subblock, if the matrix splitted). */
/* D (input) DOUBLE PRECISION array, dimension (N) */
/* The N diagonal elements of the diagonal matrix D. */
/* L (input) DOUBLE PRECISION array, dimension (N-1) */
/* The (N-1) subdiagonal elements of the unit bidiagonal */
/* matrix L. */
/* LD (input) DOUBLE PRECISION array, dimension (N-1) */
/* The (N-1) elements L(i)*D(i). */
/* CLSTRT (input) INTEGER */
/* The index of the first eigenvalue in the cluster. */
/* CLEND (input) INTEGER */
/* The index of the last eigenvalue in the cluster. */
/* W (input) DOUBLE PRECISION array, dimension >= (CLEND-CLSTRT+1) */
/* The eigenvalue APPROXIMATIONS of L D L^T in ascending order. */
/* W( CLSTRT ) through W( CLEND ) form the cluster of relatively */
/* close eigenalues. */
/* WGAP (input/output) DOUBLE PRECISION array, dimension >= (CLEND-CLSTRT+1) */
/* The separation from the right neighbor eigenvalue in W. */
/* WERR (input) DOUBLE PRECISION array, dimension >= (CLEND-CLSTRT+1) */
/* WERR contain the semiwidth of the uncertainty */
/* interval of the corresponding eigenvalue APPROXIMATION in W */
/* SPDIAM (input) estimate of the spectral diameter obtained from the */
/* Gerschgorin intervals */
/* CLGAPL, CLGAPR (input) absolute gap on each end of the cluster. */
/* Set by the calling routine to protect against shifts too close */
/* to eigenvalues outside the cluster. */
/* PIVMIN (input) DOUBLE PRECISION */
/* The minimum pivot allowed in the Sturm sequence. */
/* SIGMA (output) DOUBLE PRECISION */
/* The shift used to form L(+) D(+) L(+)^T. */
/* DPLUS (output) DOUBLE PRECISION array, dimension (N) */
/* The N diagonal elements of the diagonal matrix D(+). */
/* LPLUS (output) DOUBLE PRECISION array, dimension (N-1) */
/* The first (N-1) elements of LPLUS contain the subdiagonal */
/* elements of the unit bidiagonal matrix L(+). */
/* WORK (workspace) DOUBLE PRECISION array, dimension (2*N) */
/* Workspace. */
/* Further Details */
/* =============== */
/* Based on contributions by */
/* Beresford Parlett, University of California, Berkeley, USA */
/* Jim Demmel, University of California, Berkeley, USA */
/* Inderjit Dhillon, University of Texas, Austin, USA */
/* Osni Marques, LBNL/NERSC, USA */
/* Christof Voemel, University of California, Berkeley, USA */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Parameter adjustments */
--work;
--lplus;
--dplus;
--werr;
--wgap;
--w;
--ld;
--l;
--d__;
/* Function Body */
*info = 0;
fact = 2.;
eps = dlamch_("Precision");
shift = 0;
forcer = FALSE_;
/* Note that we cannot guarantee that for any of the shifts tried, */
/* the factorization has a small or even moderate element growth. */
/* There could be Ritz values at both ends of the cluster and despite */
/* backing off, there are examples where all factorizations tried */
/* (in IEEE mode, allowing zero pivots & infinities) have INFINITE */
/* element growth. */
/* For this reason, we should use PIVMIN in this subroutine so that at */
/* least the L D L^T factorization exists. It can be checked afterwards */
/* whether the element growth caused bad residuals/orthogonality. */
/* Decide whether the code should accept the best among all */
/* representations despite large element growth or signal INFO=1 */
nofail = TRUE_;
/* Compute the average gap length of the cluster */
clwdth = (d__1 = w[*clend] - w[*clstrt], abs(d__1)) + werr[*clend] + werr[
*clstrt];
avgap = clwdth / (doublereal) (*clend - *clstrt);
mingap = min(*clgapl,*clgapr);
/* Initial values for shifts to both ends of cluster */
/* Computing MIN */
d__1 = w[*clstrt], d__2 = w[*clend];
lsigma = min(d__1,d__2) - werr[*clstrt];
/* Computing MAX */
d__1 = w[*clstrt], d__2 = w[*clend];
rsigma = max(d__1,d__2) + werr[*clend];
/* Use a small fudge to make sure that we really shift to the outside */
lsigma -= abs(lsigma) * 4. * eps;
rsigma += abs(rsigma) * 4. * eps;
/* Compute upper bounds for how much to back off the initial shifts */
ldmax = mingap * .25 + *pivmin * 2.;
rdmax = mingap * .25 + *pivmin * 2.;
/* Computing MAX */
d__1 = avgap, d__2 = wgap[*clstrt];
ldelta = max(d__1,d__2) / fact;
/* Computing MAX */
d__1 = avgap, d__2 = wgap[*clend - 1];
rdelta = max(d__1,d__2) / fact;
/* Initialize the record of the best representation found */
s = dlamch_("S");
smlgrowth = 1. / s;
fail = (doublereal) (*n - 1) * mingap / (*spdiam * eps);
fail2 = (doublereal) (*n - 1) * mingap / (*spdiam * sqrt(eps));
bestshift = lsigma;
/* while (KTRY <= KTRYMAX) */
ktry = 0;
growthbound = *spdiam * 8.;
L5:
sawnan1 = FALSE_;
sawnan2 = FALSE_;
/* Ensure that we do not back off too much of the initial shifts */
ldelta = min(ldmax,ldelta);
rdelta = min(rdmax,rdelta);
/* Compute the element growth when shifting to both ends of the cluster */
/* accept the shift if there is no element growth at one of the two ends */
/* Left end */
s = -lsigma;
dplus[1] = d__[1] + s;
if (abs(dplus[1]) < *pivmin) {
dplus[1] = -(*pivmin);
/* Need to set SAWNAN1 because refined RRR test should not be used */
/* in this case */
sawnan1 = TRUE_;
}
max1 = abs(dplus[1]);
i__1 = *n - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
lplus[i__] = ld[i__] / dplus[i__];
s = s * lplus[i__] * l[i__] - lsigma;
dplus[i__ + 1] = d__[i__ + 1] + s;
if ((d__1 = dplus[i__ + 1], abs(d__1)) < *pivmin) {
dplus[i__ + 1] = -(*pivmin);
/* Need to set SAWNAN1 because refined RRR test should not be used */
/* in this case */
sawnan1 = TRUE_;
}
/* Computing MAX */
d__2 = max1, d__3 = (d__1 = dplus[i__ + 1], abs(d__1));
max1 = max(d__2,d__3);
/* L6: */
}
sawnan1 = sawnan1 || disnan_(&max1);
if (forcer || max1 <= growthbound && ! sawnan1) {
*sigma = lsigma;
shift = 1;
goto L100;
}
/* Right end */
s = -rsigma;
work[1] = d__[1] + s;
if (abs(work[1]) < *pivmin) {
work[1] = -(*pivmin);
/* Need to set SAWNAN2 because refined RRR test should not be used */
/* in this case */
sawnan2 = TRUE_;
}
max2 = abs(work[1]);
i__1 = *n - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
work[*n + i__] = ld[i__] / work[i__];
s = s * work[*n + i__] * l[i__] - rsigma;
work[i__ + 1] = d__[i__ + 1] + s;
if ((d__1 = work[i__ + 1], abs(d__1)) < *pivmin) {
work[i__ + 1] = -(*pivmin);
/* Need to set SAWNAN2 because refined RRR test should not be used */
/* in this case */
sawnan2 = TRUE_;
}
/* Computing MAX */
d__2 = max2, d__3 = (d__1 = work[i__ + 1], abs(d__1));
max2 = max(d__2,d__3);
/* L7: */
}
sawnan2 = sawnan2 || disnan_(&max2);
if (forcer || max2 <= growthbound && ! sawnan2) {
*sigma = rsigma;
shift = 2;
goto L100;
}
/* If we are at this point, both shifts led to too much element growth */
/* Record the better of the two shifts (provided it didn't lead to NaN) */
if (sawnan1 && sawnan2) {
/* both MAX1 and MAX2 are NaN */
goto L50;
} else {
if (! sawnan1) {
indx = 1;
if (max1 <= smlgrowth) {
smlgrowth = max1;
bestshift = lsigma;
}
}
if (! sawnan2) {
if (sawnan1 || max2 <= max1) {
indx = 2;
}
if (max2 <= smlgrowth) {
smlgrowth = max2;
bestshift = rsigma;
}
}
}
/* If we are here, both the left and the right shift led to */
/* element growth. If the element growth is moderate, then */
/* we may still accept the representation, if it passes a */
/* refined test for RRR. This test supposes that no NaN occurred. */
/* Moreover, we use the refined RRR test only for isolated clusters. */
if (clwdth < mingap / 128. && min(max1,max2) < fail2 && ! sawnan1 && !
sawnan2) {
dorrr1 = TRUE_;
} else {
dorrr1 = FALSE_;
}
tryrrr1 = TRUE_;
if (tryrrr1 && dorrr1) {
if (indx == 1) {
tmp = (d__1 = dplus[*n], abs(d__1));
znm2 = 1.;
prod = 1.;
oldp = 1.;
for (i__ = *n - 1; i__ >= 1; --i__) {
if (prod <= eps) {
prod = dplus[i__ + 1] * work[*n + i__ + 1] / (dplus[i__] *
work[*n + i__]) * oldp;
} else {
prod *= (d__1 = work[*n + i__], abs(d__1));
}
oldp = prod;
/* Computing 2nd power */
d__1 = prod;
znm2 += d__1 * d__1;
/* Computing MAX */
d__2 = tmp, d__3 = (d__1 = dplus[i__] * prod, abs(d__1));
tmp = max(d__2,d__3);
/* L15: */
}
rrr1 = tmp / (*spdiam * sqrt(znm2));
if (rrr1 <= 8.) {
*sigma = lsigma;
shift = 1;
goto L100;
}
} else if (indx == 2) {
tmp = (d__1 = work[*n], abs(d__1));
znm2 = 1.;
prod = 1.;
oldp = 1.;
for (i__ = *n - 1; i__ >= 1; --i__) {
if (prod <= eps) {
prod = work[i__ + 1] * lplus[i__ + 1] / (work[i__] *
lplus[i__]) * oldp;
} else {
prod *= (d__1 = lplus[i__], abs(d__1));
}
oldp = prod;
/* Computing 2nd power */
d__1 = prod;
znm2 += d__1 * d__1;
/* Computing MAX */
d__2 = tmp, d__3 = (d__1 = work[i__] * prod, abs(d__1));
tmp = max(d__2,d__3);
/* L16: */
}
rrr2 = tmp / (*spdiam * sqrt(znm2));
if (rrr2 <= 8.) {
*sigma = rsigma;
shift = 2;
goto L100;
}
}
}
L50:
if (ktry < 1) {
/* If we are here, both shifts failed also the RRR test. */
/* Back off to the outside */
/* Computing MAX */
d__1 = lsigma - ldelta, d__2 = lsigma - ldmax;
lsigma = max(d__1,d__2);
/* Computing MIN */
d__1 = rsigma + rdelta, d__2 = rsigma + rdmax;
rsigma = min(d__1,d__2);
ldelta *= 2.;
rdelta *= 2.;
++ktry;
goto L5;
} else {
/* None of the representations investigated satisfied our */
/* criteria. Take the best one we found. */
if (smlgrowth < fail || nofail) {
lsigma = bestshift;
rsigma = bestshift;
forcer = TRUE_;
goto L5;
} else {
*info = 1;
return 0;
}
}
L100:
if (shift == 1) {
} else if (shift == 2) {
/* store new L and D back into DPLUS, LPLUS */
dcopy_(n, &work[1], &c__1, &dplus[1], &c__1);
i__1 = *n - 1;
dcopy_(&i__1, &work[*n + 1], &c__1, &lplus[1], &c__1);
}
return 0;
/* End of DLARRF */
} /* dlarrf_ */