1 /* Copyright (c) 2007-2008 Massachusetts Institute of Technology
3 * Permission is hereby granted, free of charge, to any person obtaining
4 * a copy of this software and associated documentation files (the
5 * "Software"), to deal in the Software without restriction, including
6 * without limitation the rights to use, copy, modify, merge, publish,
7 * distribute, sublicense, and/or sell copies of the Software, and to
8 * permit persons to whom the Software is furnished to do so, subject to
9 * the following conditions:
11 * The above copyright notice and this permission notice shall be
12 * included in all copies or substantial portions of the Software.
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
15 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
16 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
17 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
18 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
19 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
20 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
27 #include "nlopt-util.h"
33 #define MIN(a,b) ((a) < (b) ? (a) : (b))
34 #define MAX(a,b) ((a) > (b) ? (a) : (b))
36 /***************************************************************************/
37 /* basic data structure:
39 * a hyper-rectangle is stored as an array of length L = 2n+3, where [1]
40 * is the value (f) of the function at the center, [0] is the "size"
41 * measure (d) of the rectangle, [3..n+2] are the coordinates of the
42 * center (c), [n+3..2n+2] are the widths of the sides (w), and [2]
43 * is an "age" measure for tie-breaking purposes.
45 * we store the hyper-rectangles in a red-black tree, sorted by (d,f)
46 * in lexographic order, to allow us to perform quick convex-hull
47 * calculations (in the future, we might make this data structure
48 * more sophisticated based on the dynamic convex-hull literature).
50 * n > 0 always, of course.
53 /* parameters of the search algorithm and various information that
54 needs to be passed around */
56 int n; /* dimension */
57 int L; /* size of each rectangle (2n+3) */
58 double magic_eps; /* Jones' epsilon parameter (1e-4 is recommended) */
59 int which_diam; /* which measure of hyper-rectangle diam to use:
60 0 = Jones, 1 = Gablonsky */
61 int which_div; /* which way to divide rects:
62 0: orig. Jones (divide all longest sides)
63 1: Gablonsky (cubes divide all, rects longest)
64 2: Jones Encyc. Opt.: pick random longest side */
65 int which_opt; /* which rects are considered "potentially optimal"
66 0: Jones (all pts on cvx hull, even equal pts)
67 1: Gablonsky DIRECT-L (pick one pt, if equal pts)
68 2: ~ 1, but pick points randomly if equal pts
69 ... 2 seems to suck compared to just picking oldest pt */
71 const double *lb, *ub;
72 nlopt_stopping *stop; /* stopping criteria */
73 nlopt_func f; void *f_data;
74 double *work; /* workspace, of length >= 2*n */
75 int *iwork; /* workspace, length >= n */
76 double minf, *xmin; /* minimum so far */
78 /* red-black tree of hyperrects, sorted by (d,f,age) in
79 lexographical order */
81 int age; /* age for next new rect */
82 double **hull; /* array to store convex hull */
83 int hull_len; /* allocated length of hull array */
86 /***************************************************************************/
88 /* Evaluate the "diameter" (d) of a rectangle of widths w[n]
90 We round the result to single precision, which should be plenty for
91 the use we put the diameter to (rect sorting), to allow our
92 performance hack in convex_hull to work (in the Jones and Gablonsky
93 DIRECT algorithms, all of the rects fall into a few diameter
94 values, and we don't want rounding error to spoil this) */
95 static double rect_diameter(int n, const double *w, const params *p)
98 if (p->which_diam == 0) { /* Jones measure */
100 for (i = 0; i < n; ++i)
102 /* distance from center to a vertex */
103 return ((float) (sqrt(sum) * 0.5));
105 else { /* Gablonsky measure */
107 for (i = 0; i < n; ++i)
110 /* half-width of longest side */
111 return ((float) (maxw * 0.5));
115 #define ALLOC_RECT(rect, L) if (!(rect = (double*) malloc(sizeof(double)*(L)))) return NLOPT_OUT_OF_MEMORY
117 static double *fv_qsort = 0;
118 static int sort_fv_compare(const void *a_, const void *b_)
120 int a = *((const int *) a_), b = *((const int *) b_);
121 double fa = MIN(fv_qsort[2*a], fv_qsort[2*a+1]);
122 double fb = MIN(fv_qsort[2*b], fv_qsort[2*b+1]);
130 static void sort_fv(int n, double *fv, int *isort)
133 for (i = 0; i < n; ++i) isort[i] = i;
134 fv_qsort = fv; /* not re-entrant, sigh... */
135 qsort(isort, (unsigned) n, sizeof(int), sort_fv_compare);
139 static double function_eval(const double *x, params *p) {
140 double f = p->f(p->n, x, NULL, p->f_data);
143 memcpy(p->xmin, x, sizeof(double) * p->n);
148 #define FUNCTION_EVAL(fv,x,p,freeonerr) fv = function_eval(x, p); if (p->minf < p->stop->minf_max) { free(freeonerr); return NLOPT_MINF_MAX_REACHED; } else if (nlopt_stop_evals((p)->stop)) { free(freeonerr); return NLOPT_MAXEVAL_REACHED; } else if (nlopt_stop_time((p)->stop)) { free(freeonerr); return NLOPT_MAXTIME_REACHED; }
150 #define THIRD (0.3333333333333333333333)
152 #define EQUAL_SIDE_TOL 5e-2 /* tolerance to equate side sizes */
154 /* divide rectangle idiv in the list p->rects */
155 static nlopt_result divide_rect(double *rdiv, params *p)
158 const const int n = p->n;
160 double *c = rdiv + 3; /* center of rect to divide */
161 double *w = c + n; /* widths of rect to divide */
163 int imax = 0, nlongest = 0;
166 for (i = 1; i < n; ++i)
169 for (i = 0; i < n; ++i)
170 if (wmax - w[i] <= wmax * EQUAL_SIDE_TOL)
172 if (p->which_div == 1 || (p->which_div == 0 && nlongest == n)) {
173 /* trisect all longest sides, in increasing order of the average
174 function value along that direction */
175 double *fv = p->work;
176 int *isort = p->iwork;
177 for (i = 0; i < n; ++i) {
178 if (wmax - w[i] <= wmax * EQUAL_SIDE_TOL) {
180 c[i] = csave - w[i] * THIRD;
181 FUNCTION_EVAL(fv[2*i], c, p, 0);
182 c[i] = csave + w[i] * THIRD;
183 FUNCTION_EVAL(fv[2*i+1], c, p, 0);
187 fv[2*i] = fv[2*i+1] = HUGE_VAL;
190 sort_fv(n, fv, isort);
191 if (!(node = rb_tree_find(&p->rtree, rdiv)))
192 return NLOPT_FAILURE;
193 for (i = 0; i < nlongest; ++i) {
195 w[isort[i]] *= THIRD;
196 rdiv[0] = rect_diameter(n, w, p);
198 node = rb_tree_resort(&p->rtree, node);
199 for (k = 0; k <= 1; ++k) {
202 memcpy(rnew, rdiv, sizeof(double) * L);
203 rnew[3 + isort[i]] += w[isort[i]] * (2*k-1);
204 rnew[1] = fv[2*isort[i]+k];
206 if (!rb_tree_insert(&p->rtree, rnew)) {
208 return NLOPT_OUT_OF_MEMORY;
215 if (nlongest > 1 && p->which_div == 2) {
216 /* randomly choose longest side */
217 i = nlopt_iurand(nlongest);
218 for (k = 0; k < n; ++k)
219 if (wmax - w[k] <= wmax * EQUAL_SIDE_TOL) {
220 if (!i) { i = k; break; }
225 i = imax; /* trisect longest side */
226 if (!(node = rb_tree_find(&p->rtree, rdiv)))
227 return NLOPT_FAILURE;
229 rdiv[0] = rect_diameter(n, w, p);
231 node = rb_tree_resort(&p->rtree, node);
232 for (k = 0; k <= 1; ++k) {
235 memcpy(rnew, rdiv, sizeof(double) * L);
236 rnew[3 + i] += w[i] * (2*k-1);
237 FUNCTION_EVAL(rnew[1], rnew + 3, p, rnew);
239 if (!rb_tree_insert(&p->rtree, rnew)) {
241 return NLOPT_OUT_OF_MEMORY;
245 return NLOPT_SUCCESS;
248 /***************************************************************************/
249 /* Convex hull algorithm, used later to find the potentially optimal
250 points. What we really have in DIRECT is a "dynamic convex hull"
251 problem, since we are dynamically adding/removing points and
252 updating the hull, but I haven't implemented any of the fancy
253 algorithms for this problem yet. */
255 /* Find the lower convex hull of a set of points (x,y) stored in a rb-tree
256 of pointers to {x,y} arrays sorted in lexographic order by (x,y).
258 Unlike standard convex hulls, we allow redundant points on the hull,
259 and even allow duplicate points if allow_dups is nonzero.
261 The return value is the number of points in the hull, with pointers
262 stored in hull[i] (should be an array of length >= t->N).
264 static int convex_hull(rb_tree *t, double **hull, int allow_dups)
268 double xmin, xmax, yminmin, ymaxmin;
271 /* Monotone chain algorithm [Andrew, 1979]. */
275 nmax = rb_tree_max(t);
282 do { /* include any duplicate points at (xmin,yminmin) */
283 hull[nhull++] = n->k;
285 } while (n && n->k[0] == xmin && n->k[1] == yminmin);
287 hull[nhull++] = n->k;
289 if (xmin == xmax) return nhull;
291 /* set nmax = min mode with x == xmax */
293 while (nmax->k[0] == xmax)
294 nmax = rb_tree_pred(nmax); /* non-NULL since xmin != xmax */
295 nmax = rb_tree_succ(nmax);
297 /* performance hack (see also below) */
300 kshift[0] = xmax * (1 - 1e-13);
301 kshift[1] = -HUGE_VAL;
302 nmax = rb_tree_find_gt(t, kshift); /* non-NULL since xmin != xmax */
306 ymaxmin = nmax->k[1];
307 minslope = (ymaxmin - yminmin) / (xmax - xmin);
309 /* set n = first node with x != xmin */
311 while (n->k[0] == xmin)
312 n = rb_tree_succ(n); /* non-NULL since xmin != xmax */
314 /* performance hack (see also below) */
317 kshift[0] = xmin * (1 + 1e-13);
318 kshift[1] = -HUGE_VAL;
319 n = rb_tree_find_gt(t, kshift); /* non-NULL since xmin != xmax */
323 for (; n != nmax; n = rb_tree_succ(n)) {
325 if (k[1] > yminmin + (k[0] - xmin) * minslope)
328 /* performance hack: most of the points in DIRECT lie along
329 vertical lines at a few x values, and we can exploit this */
330 if (nhull && k[0] == hull[nhull - 1][0]) { /* x == previous x */
331 if (k[1] > hull[nhull - 1][1]) {
333 /* because of the round to float in rect_diameter, above,
334 it shouldn't be possible for two diameters (x values)
335 to have a fractional difference < 1e-13. Note
336 that k[0] > 0 always in DIRECT */
337 kshift[0] = k[0] * (1 + 1e-13);
338 kshift[1] = -HUGE_VAL;
339 n = rb_tree_pred(rb_tree_find_gt(t, kshift));
342 else { /* equal y values, add to hull */
349 /* remove points until we are making a "left turn" to k */
351 double *t1 = hull[nhull - 1], *t2;
353 /* because we allow equal points in our hull, we have
354 to modify the standard convex-hull algorithm slightly:
355 we need to look backwards in the hull list until we
356 find a point t2 != t1 */
360 } while (it2 >= 0 && t2[0] == t1[0] && t2[1] == t1[1]);
363 /* cross product (t1-t2) x (k-t2) > 0 for a left turn: */
364 if ((t1[0]-t2[0]) * (k[1]-t2[1])
365 - (t1[1]-t2[1]) * (k[0]-t2[0]) >= 0)
373 do { /* include any duplicate points at (xmax,ymaxmin) */
374 hull[nhull++] = nmax->k;
375 nmax = rb_tree_succ(nmax);
376 } while (nmax && nmax->k[0] == xmax && n->k[1] == ymaxmin);
378 hull[nhull++] = nmax->k;
383 /***************************************************************************/
385 static int small(double *w, params *p)
388 for (i = 0; i < p->n; ++i)
389 if (w[i] > p->stop->xtol_abs[i] &&
390 w[i] > (p->ub[i] - p->lb[i]) * p->stop->xtol_rel)
395 static nlopt_result divide_good_rects(params *p)
399 int nhull, i, xtol_reached = 1, divided_some = 0;
400 double magic_eps = p->magic_eps;
402 if (p->hull_len < p->rtree.N) {
403 p->hull_len += p->rtree.N;
404 p->hull = (double **) realloc(p->hull, sizeof(double*)*p->hull_len);
405 if (!p->hull) return NLOPT_OUT_OF_MEMORY;
407 nhull = convex_hull(&p->rtree, hull = p->hull, p->which_opt != 1);
409 for (i = 0; i < nhull; ++i) {
410 double K1 = -HUGE_VAL, K2 = -HUGE_VAL, K;
413 /* find unequal points before (im) and after (ip) to get slope */
414 for (im = i-1; im >= 0 && hull[im][0] == hull[i][0]; --im);
415 for (ip = i+1; ip < nhull && hull[ip][0] == hull[i][0]; ++ip);
418 K1 = (hull[i][1] - hull[im][1]) / (hull[i][0] - hull[im][0]);
420 K1 = (hull[i][1] - hull[ip][1]) / (hull[i][0] - hull[ip][0]);
422 if (hull[i][1] - K * hull[i][0]
423 <= p->minf - magic_eps * fabs(p->minf) || ip == nhull) {
424 /* "potentially optimal" rectangle, so subdivide */
425 nlopt_result ret = divide_rect(hull[i], p);
427 if (ret != NLOPT_SUCCESS) return ret;
428 xtol_reached = xtol_reached && small(hull[i] + 3+n, p);
431 /* for the DIRECT-L variant, we only divide one rectangle out
432 of all points with equal diameter and function values
433 ... note that for p->which_opt == 1, i == ip-1 should be a no-op
434 anyway, since we set allow_dups=0 in convex_hull above */
435 if (p->which_opt == 1)
436 i = ip - 1; /* skip to next unequal point for next iteration */
437 else if (p->which_opt == 2) /* like DIRECT-L but randomized */
438 i += nlopt_iurand(ip - i); /* possibly do another equal pt */
441 if (magic_eps != 0) {
443 goto divisions; /* try again */
445 else { /* WTF? divide largest rectangle with smallest f */
446 /* (note that this code actually gets called from time
447 to time, and the heuristic here seems to work well,
448 but I don't recall this situation being discussed in
450 rb_node *max = rb_tree_max(&p->rtree);
452 double wmax = max->k[0];
453 do { /* note: this loop is O(N) worst-case time */
455 pred = rb_tree_pred(max);
456 } while (pred && pred->k[0] == wmax);
457 return divide_rect(max->k, p);
460 return xtol_reached ? NLOPT_XTOL_REACHED : NLOPT_SUCCESS;
463 /***************************************************************************/
465 /* lexographic sort order (d,f,age) of hyper-rects, for red-black tree */
466 int cdirect_hyperrect_compare(double *a, double *b)
468 if (a[0] < b[0]) return -1;
469 if (a[0] > b[0]) return +1;
470 if (a[1] < b[1]) return -1;
471 if (a[1] > b[1]) return +1;
472 if (a[2] < b[2]) return -1;
473 if (a[2] > b[2]) return +1;
474 return (int) (a - b); /* tie-breaker, shouldn't be needed */
477 /***************************************************************************/
479 nlopt_result cdirect_unscaled(int n, nlopt_func f, void *f_data,
480 const double *lb, const double *ub,
483 nlopt_stopping *stop,
484 double magic_eps, int which_alg)
489 nlopt_result ret = NLOPT_OUT_OF_MEMORY;
491 p.magic_eps = magic_eps;
492 p.which_diam = which_alg % 3;
493 p.which_div = (which_alg / 3) % 3;
494 p.which_opt = (which_alg / (3*3)) % 3;
495 p.lb = lb; p.ub = ub;
508 rb_tree_init(&p.rtree, cdirect_hyperrect_compare);
510 p.work = (double *) malloc(sizeof(double) * (2*n));
511 if (!p.work) goto done;
512 p.iwork = (int *) malloc(sizeof(int) * n);
513 if (!p.iwork) goto done;
514 p.hull_len = 128; /* start with a reasonable number */
515 p.hull = (double **) malloc(sizeof(double *) * p.hull_len);
516 if (!p.hull) goto done;
518 if (!(rnew = (double *) malloc(sizeof(double) * p.L))) goto done;
519 for (i = 0; i < n; ++i) {
520 rnew[3+i] = 0.5 * (lb[i] + ub[i]);
521 rnew[3+n+i] = ub[i] - lb[i];
523 rnew[0] = rect_diameter(n, rnew+3+n, &p);
524 rnew[1] = function_eval(rnew+3, &p);
526 if (!rb_tree_insert(&p.rtree, rnew)) {
531 ret = divide_rect(rnew, &p);
532 if (ret != NLOPT_SUCCESS) goto done;
535 double minf0 = p.minf;
536 ret = divide_good_rects(&p);
537 if (ret != NLOPT_SUCCESS) goto done;
538 if (p.minf < minf0 && nlopt_stop_f(p.stop, p.minf, minf0)) {
539 ret = NLOPT_FTOL_REACHED;
545 rb_tree_destroy_with_keys(&p.rtree);
554 /* in the conventional DIRECT-type algorithm, we first rescale our
555 coordinates to a unit hypercube ... we do this simply by
556 wrapping cdirect() around cdirect_unscaled(). */
558 double cdirect_uf(int n, const double *xu, double *grad, void *d_)
560 cdirect_uf_data *d = (cdirect_uf_data *) d_;
563 for (i = 0; i < n; ++i)
564 d->x[i] = d->lb[i] + xu[i] * (d->ub[i] - d->lb[i]);
565 f = d->f(n, d->x, grad, d->f_data);
567 for (i = 0; i < n; ++i)
568 grad[i] *= d->ub[i] - d->lb[i];
572 nlopt_result cdirect(int n, nlopt_func f, void *f_data,
573 const double *lb, const double *ub,
576 nlopt_stopping *stop,
577 double magic_eps, int which_alg)
581 const double *xtol_abs_save;
584 d.f = f; d.f_data = f_data; d.lb = lb; d.ub = ub;
585 d.x = (double *) malloc(sizeof(double) * n*4);
586 if (!d.x) return NLOPT_OUT_OF_MEMORY;
588 for (i = 0; i < n; ++i) {
589 x[i] = (x[i] - lb[i]) / (ub[i] - lb[i]);
592 d.x[3*n+i] = stop->xtol_abs[i] / (ub[i] - lb[i]);
594 xtol_abs_save = stop->xtol_abs;
595 stop->xtol_abs = d.x + 3*n;
596 ret = cdirect_unscaled(n, cdirect_uf, &d, d.x+n, d.x+2*n, x, minf, stop,
597 magic_eps, which_alg);
598 stop->xtol_abs = xtol_abs_save;
599 for (i = 0; i < n; ++i)
600 x[i] = lb[i]+ x[i] * (ub[i] - lb[i]);