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171 lines
4.1 KiB
C
171 lines
4.1 KiB
C
#include "clapack.h"
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/* Subroutine */ int slarrc_(char *jobt, integer *n, real *vl, real *vu, real
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*d__, real *e, real *pivmin, integer *eigcnt, integer *lcnt, integer *
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rcnt, integer *info)
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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;
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/* Local variables */
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integer i__;
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real sl, su, tmp, tmp2;
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logical matt;
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extern logical lsame_(char *, char *);
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real lpivot, rpivot;
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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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/* Find the number of eigenvalues of the symmetric tridiagonal matrix T */
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/* that are in the interval (VL,VU] if JOBT = 'T', and of L D L^T */
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/* if JOBT = 'L'. */
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/* Arguments */
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/* ========= */
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/* JOBT (input) CHARACTER*1 */
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/* = 'T': Compute Sturm count for matrix T. */
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/* = 'L': Compute Sturm count for matrix L D L^T. */
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/* N (input) INTEGER */
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/* The order of the matrix. N > 0. */
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/* VL (input) DOUBLE PRECISION */
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/* VU (input) DOUBLE PRECISION */
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/* The lower and upper bounds for the eigenvalues. */
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/* D (input) DOUBLE PRECISION array, dimension (N) */
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/* JOBT = 'T': The N diagonal elements of the tridiagonal matrix T. */
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/* JOBT = 'L': The N diagonal elements of the diagonal matrix D. */
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/* E (input) DOUBLE PRECISION array, dimension (N) */
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/* JOBT = 'T': The N-1 offdiagonal elements of the matrix T. */
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/* JOBT = 'L': The N-1 offdiagonal elements of the matrix L. */
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/* PIVMIN (input) DOUBLE PRECISION */
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/* The minimum pivot in the Sturm sequence for T. */
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/* EIGCNT (output) INTEGER */
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/* The number of eigenvalues of the symmetric tridiagonal matrix T */
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/* that are in the interval (VL,VU] */
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/* LCNT (output) INTEGER */
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/* RCNT (output) INTEGER */
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/* The left and right negcounts of the interval. */
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/* INFO (output) INTEGER */
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/* Further Details */
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/* =============== */
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/* Based on contributions by */
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/* Beresford Parlett, University of California, Berkeley, USA */
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/* Jim Demmel, University of California, Berkeley, USA */
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/* Inderjit Dhillon, University of Texas, Austin, USA */
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/* Osni Marques, LBNL/NERSC, USA */
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/* Christof Voemel, University of California, Berkeley, USA */
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/* ===================================================================== */
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/* .. Parameters .. */
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/* .. */
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/* .. Local Scalars .. */
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/* .. */
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/* .. External Functions .. */
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/* .. */
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/* .. Executable Statements .. */
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/* Parameter adjustments */
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--e;
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--d__;
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/* Function Body */
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*info = 0;
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*lcnt = 0;
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*rcnt = 0;
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*eigcnt = 0;
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matt = lsame_(jobt, "T");
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if (matt) {
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/* Sturm sequence count on T */
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lpivot = d__[1] - *vl;
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rpivot = d__[1] - *vu;
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if (lpivot <= 0.f) {
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++(*lcnt);
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}
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if (rpivot <= 0.f) {
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++(*rcnt);
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}
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i__1 = *n - 1;
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for (i__ = 1; i__ <= i__1; ++i__) {
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/* Computing 2nd power */
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r__1 = e[i__];
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tmp = r__1 * r__1;
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lpivot = d__[i__ + 1] - *vl - tmp / lpivot;
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rpivot = d__[i__ + 1] - *vu - tmp / rpivot;
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if (lpivot <= 0.f) {
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++(*lcnt);
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}
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if (rpivot <= 0.f) {
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++(*rcnt);
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}
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/* L10: */
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}
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} else {
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/* Sturm sequence count on L D L^T */
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sl = -(*vl);
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su = -(*vu);
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i__1 = *n - 1;
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for (i__ = 1; i__ <= i__1; ++i__) {
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lpivot = d__[i__] + sl;
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rpivot = d__[i__] + su;
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if (lpivot <= 0.f) {
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++(*lcnt);
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}
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if (rpivot <= 0.f) {
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++(*rcnt);
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}
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tmp = e[i__] * d__[i__] * e[i__];
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tmp2 = tmp / lpivot;
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if (tmp2 == 0.f) {
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sl = tmp - *vl;
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} else {
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sl = sl * tmp2 - *vl;
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}
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tmp2 = tmp / rpivot;
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if (tmp2 == 0.f) {
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su = tmp - *vu;
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} else {
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su = su * tmp2 - *vu;
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}
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/* L20: */
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}
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lpivot = d__[*n] + sl;
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rpivot = d__[*n] + su;
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if (lpivot <= 0.f) {
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++(*lcnt);
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}
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if (rpivot <= 0.f) {
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++(*rcnt);
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}
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}
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*eigcnt = *rcnt - *lcnt;
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return 0;
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/* end of SLARRC */
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} /* slarrc_ */
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