194 lines
4.6 KiB
C
194 lines
4.6 KiB
C
#include "clapack.h"
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/* Subroutine */ int slasq6_(integer *i0, integer *n0, real *z__, integer *pp,
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real *dmin__, real *dmin1, real *dmin2, real *dn, real *dnm1, real *
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dnm2)
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{
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/* System generated locals */
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integer i__1;
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real r__1, r__2;
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/* Local variables */
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real d__;
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integer j4, j4p2;
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real emin, temp;
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extern doublereal slamch_(char *);
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real safmin;
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/* -- LAPACK auxiliary routine (version 3.1) -- */
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/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
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/* November 2006 */
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/* .. Scalar Arguments .. */
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/* .. */
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/* .. Array Arguments .. */
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/* .. */
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/* Purpose */
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/* ======= */
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/* SLASQ6 computes one dqd (shift equal to zero) transform in */
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/* ping-pong form, with protection against underflow and overflow. */
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/* Arguments */
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/* ========= */
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/* I0 (input) INTEGER */
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/* First index. */
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/* N0 (input) INTEGER */
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/* Last index. */
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/* Z (input) REAL array, dimension ( 4*N ) */
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/* Z holds the qd array. EMIN is stored in Z(4*N0) to avoid */
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/* an extra argument. */
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/* PP (input) INTEGER */
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/* PP=0 for ping, PP=1 for pong. */
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/* DMIN (output) REAL */
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/* Minimum value of d. */
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/* DMIN1 (output) REAL */
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/* Minimum value of d, excluding D( N0 ). */
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/* DMIN2 (output) REAL */
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/* Minimum value of d, excluding D( N0 ) and D( N0-1 ). */
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/* DN (output) REAL */
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/* d(N0), the last value of d. */
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/* DNM1 (output) REAL */
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/* d(N0-1). */
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/* DNM2 (output) REAL */
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/* d(N0-2). */
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/* ===================================================================== */
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/* .. Parameter .. */
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/* .. */
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/* .. Local Scalars .. */
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/* .. */
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/* .. External Function .. */
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/* .. */
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/* .. Intrinsic Functions .. */
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/* .. */
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/* .. Executable Statements .. */
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/* Parameter adjustments */
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--z__;
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/* Function Body */
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if (*n0 - *i0 - 1 <= 0) {
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return 0;
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}
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safmin = slamch_("Safe minimum");
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j4 = (*i0 << 2) + *pp - 3;
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emin = z__[j4 + 4];
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d__ = z__[j4];
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*dmin__ = d__;
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if (*pp == 0) {
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i__1 = *n0 - 3 << 2;
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for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
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z__[j4 - 2] = d__ + z__[j4 - 1];
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if (z__[j4 - 2] == 0.f) {
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z__[j4] = 0.f;
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d__ = z__[j4 + 1];
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*dmin__ = d__;
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emin = 0.f;
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} else if (safmin * z__[j4 + 1] < z__[j4 - 2] && safmin * z__[j4
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- 2] < z__[j4 + 1]) {
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temp = z__[j4 + 1] / z__[j4 - 2];
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z__[j4] = z__[j4 - 1] * temp;
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d__ *= temp;
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} else {
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z__[j4] = z__[j4 + 1] * (z__[j4 - 1] / z__[j4 - 2]);
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d__ = z__[j4 + 1] * (d__ / z__[j4 - 2]);
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}
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*dmin__ = dmin(*dmin__,d__);
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/* Computing MIN */
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r__1 = emin, r__2 = z__[j4];
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emin = dmin(r__1,r__2);
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/* L10: */
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}
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} else {
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i__1 = *n0 - 3 << 2;
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for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
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z__[j4 - 3] = d__ + z__[j4];
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if (z__[j4 - 3] == 0.f) {
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z__[j4 - 1] = 0.f;
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d__ = z__[j4 + 2];
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*dmin__ = d__;
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emin = 0.f;
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} else if (safmin * z__[j4 + 2] < z__[j4 - 3] && safmin * z__[j4
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- 3] < z__[j4 + 2]) {
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temp = z__[j4 + 2] / z__[j4 - 3];
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z__[j4 - 1] = z__[j4] * temp;
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d__ *= temp;
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} else {
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z__[j4 - 1] = z__[j4 + 2] * (z__[j4] / z__[j4 - 3]);
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d__ = z__[j4 + 2] * (d__ / z__[j4 - 3]);
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}
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*dmin__ = dmin(*dmin__,d__);
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/* Computing MIN */
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r__1 = emin, r__2 = z__[j4 - 1];
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emin = dmin(r__1,r__2);
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/* L20: */
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}
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}
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/* Unroll last two steps. */
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*dnm2 = d__;
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*dmin2 = *dmin__;
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j4 = (*n0 - 2 << 2) - *pp;
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j4p2 = j4 + (*pp << 1) - 1;
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z__[j4 - 2] = *dnm2 + z__[j4p2];
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if (z__[j4 - 2] == 0.f) {
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z__[j4] = 0.f;
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*dnm1 = z__[j4p2 + 2];
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*dmin__ = *dnm1;
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emin = 0.f;
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} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
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z__[j4p2 + 2]) {
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temp = z__[j4p2 + 2] / z__[j4 - 2];
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z__[j4] = z__[j4p2] * temp;
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*dnm1 = *dnm2 * temp;
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} else {
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z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
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*dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]);
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}
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*dmin__ = dmin(*dmin__,*dnm1);
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*dmin1 = *dmin__;
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j4 += 4;
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j4p2 = j4 + (*pp << 1) - 1;
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z__[j4 - 2] = *dnm1 + z__[j4p2];
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if (z__[j4 - 2] == 0.f) {
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z__[j4] = 0.f;
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*dn = z__[j4p2 + 2];
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*dmin__ = *dn;
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emin = 0.f;
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} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
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z__[j4p2 + 2]) {
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temp = z__[j4p2 + 2] / z__[j4 - 2];
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z__[j4] = z__[j4p2] * temp;
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*dn = *dnm1 * temp;
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} else {
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z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
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*dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]);
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}
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*dmin__ = dmin(*dmin__,*dn);
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z__[j4 + 2] = *dn;
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z__[(*n0 << 2) - *pp] = emin;
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return 0;
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/* End of SLASQ6 */
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} /* slasq6_ */
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