3 /* Subroutine */ int slasq3_(integer *i0, integer *n0, real *z__, integer *pp,
4 real *dmin__, real *sigma, real *desig, real *qmax, integer *nfail,
5 integer *iter, integer *ndiv, logical *ieee)
9 static integer ttype = 0;
10 static real dmin1 = 0.f;
11 static real dmin2 = 0.f;
13 static real dn1 = 0.f;
14 static real dn2 = 0.f;
15 static real tau = 0.f;
17 /* System generated locals */
21 /* Builtin functions */
22 double sqrt(doublereal);
30 extern /* Subroutine */ int slasq4_(integer *, integer *, real *, integer
31 *, integer *, real *, real *, real *, real *, real *, real *,
32 real *, integer *), slasq5_(integer *, integer *, real *, integer
33 *, real *, real *, real *, real *, real *, real *, real *,
34 logical *), slasq6_(integer *, integer *, real *, integer *, real
35 *, real *, real *, real *, real *, real *);
36 extern doublereal slamch_(char *);
40 /* -- LAPACK auxiliary routine (version 3.1) -- */
41 /* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
44 /* .. Scalar Arguments .. */
46 /* .. Array Arguments .. */
52 /* SLASQ3 checks for deflation, computes a shift (TAU) and calls dqds. */
53 /* In case of failure it changes shifts, and tries again until output */
59 /* I0 (input) INTEGER */
62 /* N0 (input) INTEGER */
65 /* Z (input) REAL array, dimension ( 4*N ) */
66 /* Z holds the qd array. */
68 /* PP (input) INTEGER */
69 /* PP=0 for ping, PP=1 for pong. */
71 /* DMIN (output) REAL */
72 /* Minimum value of d. */
74 /* SIGMA (output) REAL */
75 /* Sum of shifts used in current segment. */
77 /* DESIG (input/output) REAL */
78 /* Lower order part of SIGMA */
80 /* QMAX (input) REAL */
81 /* Maximum value of q. */
83 /* NFAIL (output) INTEGER */
84 /* Number of times shift was too big. */
86 /* ITER (output) INTEGER */
87 /* Number of iterations. */
89 /* NDIV (output) INTEGER */
90 /* Number of divisions. */
92 /* TTYPE (output) INTEGER */
95 /* IEEE (input) LOGICAL */
96 /* Flag for IEEE or non IEEE arithmetic (passed to SLASQ5). */
98 /* ===================================================================== */
100 /* .. Parameters .. */
102 /* .. Local Scalars .. */
104 /* .. External Subroutines .. */
106 /* .. External Function .. */
108 /* .. Intrinsic Functions .. */
110 /* .. Save statement .. */
112 /* .. Data statement .. */
113 /* Parameter adjustments */
118 /* .. Executable Statements .. */
121 eps = slamch_("Precision");
122 safmin = slamch_("Safe minimum");
124 /* Computing 2nd power */
128 /* Check for deflation. */
138 nn = (*n0 << 2) + *pp;
139 if (*n0 == *i0 + 1) {
143 /* Check whether E(N0-1) is negligible, 1 eigenvalue. */
145 if (z__[nn - 5] > tol2 * (*sigma + z__[nn - 3]) && z__[nn - (*pp << 1) -
146 4] > tol2 * z__[nn - 7]) {
152 z__[(*n0 << 2) - 3] = z__[(*n0 << 2) + *pp - 3] + *sigma;
156 /* Check whether E(N0-2) is negligible, 2 eigenvalues. */
160 if (z__[nn - 9] > tol2 * *sigma && z__[nn - (*pp << 1) - 8] > tol2 * z__[
167 if (z__[nn - 3] > z__[nn - 7]) {
169 z__[nn - 3] = z__[nn - 7];
172 if (z__[nn - 5] > z__[nn - 3] * tol2) {
173 t = (z__[nn - 7] - z__[nn - 3] + z__[nn - 5]) * .5f;
174 s = z__[nn - 3] * (z__[nn - 5] / t);
176 s = z__[nn - 3] * (z__[nn - 5] / (t * (sqrt(s / t + 1.f) + 1.f)));
178 s = z__[nn - 3] * (z__[nn - 5] / (t + sqrt(t) * sqrt(t + s)));
180 t = z__[nn - 7] + (s + z__[nn - 5]);
181 z__[nn - 3] *= z__[nn - 7] / t;
184 z__[(*n0 << 2) - 7] = z__[nn - 7] + *sigma;
185 z__[(*n0 << 2) - 3] = z__[nn - 3] + *sigma;
191 /* Reverse the qd-array, if warranted. */
193 if (*dmin__ <= 0.f || *n0 < n0in) {
194 if (z__[(*i0 << 2) + *pp - 3] * 1.5f < z__[(*n0 << 2) + *pp - 3]) {
195 ipn4 = *i0 + *n0 << 2;
196 i__1 = *i0 + *n0 - 1 << 1;
197 for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
199 z__[j4 - 3] = z__[ipn4 - j4 - 3];
200 z__[ipn4 - j4 - 3] = temp;
202 z__[j4 - 2] = z__[ipn4 - j4 - 2];
203 z__[ipn4 - j4 - 2] = temp;
205 z__[j4 - 1] = z__[ipn4 - j4 - 5];
206 z__[ipn4 - j4 - 5] = temp;
208 z__[j4] = z__[ipn4 - j4 - 4];
209 z__[ipn4 - j4 - 4] = temp;
212 if (*n0 - *i0 <= 4) {
213 z__[(*n0 << 2) + *pp - 1] = z__[(*i0 << 2) + *pp - 1];
214 z__[(*n0 << 2) - *pp] = z__[(*i0 << 2) - *pp];
217 r__1 = dmin2, r__2 = z__[(*n0 << 2) + *pp - 1];
218 dmin2 = dmin(r__1,r__2);
220 r__1 = z__[(*n0 << 2) + *pp - 1], r__2 = z__[(*i0 << 2) + *pp - 1]
221 , r__1 = min(r__1,r__2), r__2 = z__[(*i0 << 2) + *pp + 3];
222 z__[(*n0 << 2) + *pp - 1] = dmin(r__1,r__2);
224 r__1 = z__[(*n0 << 2) - *pp], r__2 = z__[(*i0 << 2) - *pp], r__1 =
225 min(r__1,r__2), r__2 = z__[(*i0 << 2) - *pp + 4];
226 z__[(*n0 << 2) - *pp] = dmin(r__1,r__2);
228 r__1 = *qmax, r__2 = z__[(*i0 << 2) + *pp - 3], r__1 = max(r__1,
229 r__2), r__2 = z__[(*i0 << 2) + *pp + 1];
230 *qmax = dmax(r__1,r__2);
236 r__1 = z__[(*n0 << 2) + *pp - 1], r__2 = z__[(*n0 << 2) + *pp - 9], r__1 =
237 min(r__1,r__2), r__2 = dmin2 + z__[(*n0 << 2) - *pp];
238 if (*dmin__ < 0.f || safmin * *qmax < dmin(r__1,r__2)) {
240 /* Choose a shift. */
242 slasq4_(i0, n0, &z__[1], pp, &n0in, dmin__, &dmin1, &dmin2, &dn, &dn1,
245 /* Call dqds until DMIN > 0. */
249 slasq5_(i0, n0, &z__[1], pp, &tau, dmin__, &dmin1, &dmin2, &dn, &dn1,
252 *ndiv += *n0 - *i0 + 2;
257 if (*dmin__ >= 0.f && dmin1 > 0.f) {
263 } else if (*dmin__ < 0.f && dmin1 > 0.f && z__[(*n0 - 1 << 2) - *pp] <
264 tol * (*sigma + dn1) && dabs(dn) < tol * *sigma) {
266 /* Convergence hidden by negative DN. */
268 z__[(*n0 - 1 << 2) - *pp + 2] = 0.f;
271 } else if (*dmin__ < 0.f) {
273 /* TAU too big. Select new TAU and try again. */
278 /* Failed twice. Play it safe. */
281 } else if (dmin1 > 0.f) {
283 /* Late failure. Gives excellent shift. */
285 tau = (tau + *dmin__) * (1.f - eps * 2.f);
289 /* Early failure. Divide by 4. */
295 } else if (*dmin__ != *dmin__) {
303 /* Possible underflow. Play it safe. */
309 /* Risk of underflow. */
312 slasq6_(i0, n0, &z__[1], pp, dmin__, &dmin1, &dmin2, &dn, &dn1, &dn2);
313 *ndiv += *n0 - *i0 + 2;
321 *desig -= t - *sigma;
324 *desig = *sigma - (t - tau) + *desig;