3 /* Subroutine */ int dlazq3_(integer *i0, integer *n0, doublereal *z__,
4 integer *pp, doublereal *dmin__, doublereal *sigma, doublereal *desig,
5 doublereal *qmax, integer *nfail, integer *iter, integer *ndiv,
6 logical *ieee, integer *ttype, doublereal *dmin1, doublereal *dmin2,
7 doublereal *dn, doublereal *dn1, doublereal *dn2, doublereal *tau)
9 /* System generated locals */
11 doublereal d__1, d__2;
13 /* Builtin functions */
14 double sqrt(doublereal);
21 doublereal tol2, temp;
22 extern /* Subroutine */ int dlasq5_(integer *, integer *, doublereal *,
23 integer *, doublereal *, doublereal *, doublereal *, doublereal *,
24 doublereal *, doublereal *, doublereal *, logical *), dlasq6_(
25 integer *, integer *, doublereal *, integer *, doublereal *,
26 doublereal *, doublereal *, doublereal *, doublereal *,
27 doublereal *), dlazq4_(integer *, integer *, doublereal *,
28 integer *, integer *, doublereal *, doublereal *, doublereal *,
29 doublereal *, doublereal *, doublereal *, doublereal *, integer *,
31 extern doublereal dlamch_(char *);
35 /* -- LAPACK auxiliary routine (version 3.1) -- */
36 /* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
39 /* .. Scalar Arguments .. */
41 /* .. Array Arguments .. */
47 /* DLAZQ3 checks for deflation, computes a shift (TAU) and calls dqds. */
48 /* In case of failure it changes shifts, and tries again until output */
54 /* I0 (input) INTEGER */
57 /* N0 (input) INTEGER */
60 /* Z (input) DOUBLE PRECISION array, dimension ( 4*N ) */
61 /* Z holds the qd array. */
63 /* PP (input) INTEGER */
64 /* PP=0 for ping, PP=1 for pong. */
66 /* DMIN (output) DOUBLE PRECISION */
67 /* Minimum value of d. */
69 /* SIGMA (output) DOUBLE PRECISION */
70 /* Sum of shifts used in current segment. */
72 /* DESIG (input/output) DOUBLE PRECISION */
73 /* Lower order part of SIGMA */
75 /* QMAX (input) DOUBLE PRECISION */
76 /* Maximum value of q. */
78 /* NFAIL (output) INTEGER */
79 /* Number of times shift was too big. */
81 /* ITER (output) INTEGER */
82 /* Number of iterations. */
84 /* NDIV (output) INTEGER */
85 /* Number of divisions. */
87 /* IEEE (input) LOGICAL */
88 /* Flag for IEEE or non IEEE arithmetic (passed to DLASQ5). */
90 /* TTYPE (input/output) INTEGER */
91 /* Shift type. TTYPE is passed as an argument in order to save */
92 /* its value between calls to DLAZQ3 */
94 /* DMIN1 (input/output) REAL */
95 /* DMIN2 (input/output) REAL */
96 /* DN (input/output) REAL */
97 /* DN1 (input/output) REAL */
98 /* DN2 (input/output) REAL */
99 /* TAU (input/output) REAL */
100 /* These are passed as arguments in order to save their values */
101 /* between calls to DLAZQ3 */
103 /* This is a thread safe version of DLASQ3, which passes TTYPE, DMIN1, */
104 /* DMIN2, DN, DN1. DN2 and TAU through the argument list in place of */
105 /* declaring them in a SAVE statment. */
107 /* ===================================================================== */
109 /* .. Parameters .. */
111 /* .. Local Scalars .. */
113 /* .. External Subroutines .. */
115 /* .. External Function .. */
117 /* .. Intrinsic Functions .. */
119 /* .. Executable Statements .. */
121 /* Parameter adjustments */
126 eps = dlamch_("Precision");
127 safmin = dlamch_("Safe minimum");
129 /* Computing 2nd power */
134 /* Check for deflation. */
144 nn = (*n0 << 2) + *pp;
145 if (*n0 == *i0 + 1) {
149 /* Check whether E(N0-1) is negligible, 1 eigenvalue. */
151 if (z__[nn - 5] > tol2 * (*sigma + z__[nn - 3]) && z__[nn - (*pp << 1) -
152 4] > tol2 * z__[nn - 7]) {
158 z__[(*n0 << 2) - 3] = z__[(*n0 << 2) + *pp - 3] + *sigma;
162 /* Check whether E(N0-2) is negligible, 2 eigenvalues. */
166 if (z__[nn - 9] > tol2 * *sigma && z__[nn - (*pp << 1) - 8] > tol2 * z__[
173 if (z__[nn - 3] > z__[nn - 7]) {
175 z__[nn - 3] = z__[nn - 7];
178 if (z__[nn - 5] > z__[nn - 3] * tol2) {
179 t = (z__[nn - 7] - z__[nn - 3] + z__[nn - 5]) * .5;
180 s = z__[nn - 3] * (z__[nn - 5] / t);
182 s = z__[nn - 3] * (z__[nn - 5] / (t * (sqrt(s / t + 1.) + 1.)));
184 s = z__[nn - 3] * (z__[nn - 5] / (t + sqrt(t) * sqrt(t + s)));
186 t = z__[nn - 7] + (s + z__[nn - 5]);
187 z__[nn - 3] *= z__[nn - 7] / t;
190 z__[(*n0 << 2) - 7] = z__[nn - 7] + *sigma;
191 z__[(*n0 << 2) - 3] = z__[nn - 3] + *sigma;
197 /* Reverse the qd-array, if warranted. */
199 if (*dmin__ <= 0. || *n0 < n0in) {
200 if (z__[(*i0 << 2) + *pp - 3] * 1.5 < z__[(*n0 << 2) + *pp - 3]) {
201 ipn4 = *i0 + *n0 << 2;
202 i__1 = *i0 + *n0 - 1 << 1;
203 for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
205 z__[j4 - 3] = z__[ipn4 - j4 - 3];
206 z__[ipn4 - j4 - 3] = temp;
208 z__[j4 - 2] = z__[ipn4 - j4 - 2];
209 z__[ipn4 - j4 - 2] = temp;
211 z__[j4 - 1] = z__[ipn4 - j4 - 5];
212 z__[ipn4 - j4 - 5] = temp;
214 z__[j4] = z__[ipn4 - j4 - 4];
215 z__[ipn4 - j4 - 4] = temp;
218 if (*n0 - *i0 <= 4) {
219 z__[(*n0 << 2) + *pp - 1] = z__[(*i0 << 2) + *pp - 1];
220 z__[(*n0 << 2) - *pp] = z__[(*i0 << 2) - *pp];
223 d__1 = *dmin2, d__2 = z__[(*n0 << 2) + *pp - 1];
224 *dmin2 = min(d__1,d__2);
226 d__1 = z__[(*n0 << 2) + *pp - 1], d__2 = z__[(*i0 << 2) + *pp - 1]
227 , d__1 = min(d__1,d__2), d__2 = z__[(*i0 << 2) + *pp + 3];
228 z__[(*n0 << 2) + *pp - 1] = min(d__1,d__2);
230 d__1 = z__[(*n0 << 2) - *pp], d__2 = z__[(*i0 << 2) - *pp], d__1 =
231 min(d__1,d__2), d__2 = z__[(*i0 << 2) - *pp + 4];
232 z__[(*n0 << 2) - *pp] = min(d__1,d__2);
234 d__1 = *qmax, d__2 = z__[(*i0 << 2) + *pp - 3], d__1 = max(d__1,
235 d__2), d__2 = z__[(*i0 << 2) + *pp + 1];
236 *qmax = max(d__1,d__2);
242 d__1 = z__[(*n0 << 2) + *pp - 1], d__2 = z__[(*n0 << 2) + *pp - 9], d__1 =
243 min(d__1,d__2), d__2 = *dmin2 + z__[(*n0 << 2) - *pp];
244 if (*dmin__ < 0. || safmin * *qmax < min(d__1,d__2)) {
246 /* Choose a shift. */
248 dlazq4_(i0, n0, &z__[1], pp, &n0in, dmin__, dmin1, dmin2, dn, dn1,
249 dn2, tau, ttype, &g);
251 /* Call dqds until DMIN > 0. */
255 dlasq5_(i0, n0, &z__[1], pp, tau, dmin__, dmin1, dmin2, dn, dn1, dn2,
258 *ndiv += *n0 - *i0 + 2;
263 if (*dmin__ >= 0. && *dmin1 > 0.) {
269 } else if (*dmin__ < 0. && *dmin1 > 0. && z__[(*n0 - 1 << 2) - *pp] <
270 tol * (*sigma + *dn1) && abs(*dn) < tol * *sigma) {
272 /* Convergence hidden by negative DN. */
274 z__[(*n0 - 1 << 2) - *pp + 2] = 0.;
277 } else if (*dmin__ < 0.) {
279 /* TAU too big. Select new TAU and try again. */
284 /* Failed twice. Play it safe. */
287 } else if (*dmin1 > 0.) {
289 /* Late failure. Gives excellent shift. */
291 *tau = (*tau + *dmin__) * (1. - eps * 2.);
295 /* Early failure. Divide by 4. */
301 } else if (*dmin__ != *dmin__) {
309 /* Possible underflow. Play it safe. */
315 /* Risk of underflow. */
318 dlasq6_(i0, n0, &z__[1], pp, dmin__, dmin1, dmin2, dn, dn1, dn2);
319 *ndiv += *n0 - *i0 + 2;
327 *desig -= t - *sigma;
330 *desig = *sigma - (t - *tau) + *desig;