3 /* Subroutine */ int dlasq6_(integer *i0, integer *n0, doublereal *z__,
4 integer *pp, doublereal *dmin__, doublereal *dmin1, doublereal *dmin2,
5 doublereal *dn, doublereal *dnm1, doublereal *dnm2)
7 /* System generated locals */
14 doublereal emin, temp;
15 extern doublereal dlamch_(char *);
19 /* -- LAPACK auxiliary routine (version 3.1) -- */
20 /* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
23 /* .. Scalar Arguments .. */
25 /* .. Array Arguments .. */
31 /* DLASQ6 computes one dqd (shift equal to zero) transform in */
32 /* ping-pong form, with protection against underflow and overflow. */
37 /* I0 (input) INTEGER */
40 /* N0 (input) INTEGER */
43 /* Z (input) DOUBLE PRECISION array, dimension ( 4*N ) */
44 /* Z holds the qd array. EMIN is stored in Z(4*N0) to avoid */
45 /* an extra argument. */
47 /* PP (input) INTEGER */
48 /* PP=0 for ping, PP=1 for pong. */
50 /* DMIN (output) DOUBLE PRECISION */
51 /* Minimum value of d. */
53 /* DMIN1 (output) DOUBLE PRECISION */
54 /* Minimum value of d, excluding D( N0 ). */
56 /* DMIN2 (output) DOUBLE PRECISION */
57 /* Minimum value of d, excluding D( N0 ) and D( N0-1 ). */
59 /* DN (output) DOUBLE PRECISION */
60 /* d(N0), the last value of d. */
62 /* DNM1 (output) DOUBLE PRECISION */
65 /* DNM2 (output) DOUBLE PRECISION */
68 /* ===================================================================== */
72 /* .. Local Scalars .. */
74 /* .. External Function .. */
76 /* .. Intrinsic Functions .. */
78 /* .. Executable Statements .. */
80 /* Parameter adjustments */
84 if (*n0 - *i0 - 1 <= 0) {
88 safmin = dlamch_("Safe minimum");
89 j4 = (*i0 << 2) + *pp - 3;
96 for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
97 z__[j4 - 2] = d__ + z__[j4 - 1];
98 if (z__[j4 - 2] == 0.) {
103 } else if (safmin * z__[j4 + 1] < z__[j4 - 2] && safmin * z__[j4
104 - 2] < z__[j4 + 1]) {
105 temp = z__[j4 + 1] / z__[j4 - 2];
106 z__[j4] = z__[j4 - 1] * temp;
109 z__[j4] = z__[j4 + 1] * (z__[j4 - 1] / z__[j4 - 2]);
110 d__ = z__[j4 + 1] * (d__ / z__[j4 - 2]);
112 *dmin__ = min(*dmin__,d__);
114 d__1 = emin, d__2 = z__[j4];
115 emin = min(d__1,d__2);
120 for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
121 z__[j4 - 3] = d__ + z__[j4];
122 if (z__[j4 - 3] == 0.) {
127 } else if (safmin * z__[j4 + 2] < z__[j4 - 3] && safmin * z__[j4
128 - 3] < z__[j4 + 2]) {
129 temp = z__[j4 + 2] / z__[j4 - 3];
130 z__[j4 - 1] = z__[j4] * temp;
133 z__[j4 - 1] = z__[j4 + 2] * (z__[j4] / z__[j4 - 3]);
134 d__ = z__[j4 + 2] * (d__ / z__[j4 - 3]);
136 *dmin__ = min(*dmin__,d__);
138 d__1 = emin, d__2 = z__[j4 - 1];
139 emin = min(d__1,d__2);
144 /* Unroll last two steps. */
148 j4 = (*n0 - 2 << 2) - *pp;
149 j4p2 = j4 + (*pp << 1) - 1;
150 z__[j4 - 2] = *dnm2 + z__[j4p2];
151 if (z__[j4 - 2] == 0.) {
153 *dnm1 = z__[j4p2 + 2];
156 } else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
158 temp = z__[j4p2 + 2] / z__[j4 - 2];
159 z__[j4] = z__[j4p2] * temp;
160 *dnm1 = *dnm2 * temp;
162 z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
163 *dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]);
165 *dmin__ = min(*dmin__,*dnm1);
169 j4p2 = j4 + (*pp << 1) - 1;
170 z__[j4 - 2] = *dnm1 + z__[j4p2];
171 if (z__[j4 - 2] == 0.) {
176 } else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
178 temp = z__[j4p2 + 2] / z__[j4 - 2];
179 z__[j4] = z__[j4p2] * temp;
182 z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
183 *dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]);
185 *dmin__ = min(*dmin__,*dn);
188 z__[(*n0 << 2) - *pp] = emin;