src/surf/maxmin.c

   1 /*      $Id$     */
   2
   3 /* Copyright (c) 2004 Arnaud Legrand. All rights reserved.                  */
   4
   5 /* This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the license (GNU LGPL) which comes with this package. */
   7
   8
   9 #include "xbt/sysdep.h"
  10 #include "xbt/log.h"
  11 #include "xbt/mallocator.h"
  12 #include "maxmin_private.h"
  13 #include <stdlib.h>
  14 #include <stdio.h> /* sprintf */
  15 #include <math.h>
  16 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(surf_maxmin, surf,
  17                                 "Logging specific to SURF (maxmin)");
  18
  19 static void *lmm_variable_mallocator_new_f(void);
  20 static void lmm_variable_mallocator_free_f(void *var);
  21 static void lmm_variable_mallocator_reset_f(void *var);
  22
  23 lmm_system_t lmm_system_new(void)
  24 {
  25   lmm_system_t l = NULL;
  26   s_lmm_variable_t var;
  27   s_lmm_constraint_t cnst;
  28
  29   l = xbt_new0(s_lmm_system_t, 1);
  30
  31   l->modified = 0;
  32   xbt_swag_init(&(l->variable_set),
  33                 xbt_swag_offset(var, variable_set_hookup));
  34   xbt_swag_init(&(l->constraint_set),
  35                 xbt_swag_offset(cnst, constraint_set_hookup));
  36
  37   xbt_swag_init(&(l->active_constraint_set),
  38                 xbt_swag_offset(cnst, active_constraint_set_hookup));
  39
  40   xbt_swag_init(&(l->saturated_variable_set),
  41                 xbt_swag_offset(var, saturated_variable_set_hookup));
  42   xbt_swag_init(&(l->saturated_constraint_set),
  43                 xbt_swag_offset(cnst, saturated_constraint_set_hookup));
  44
  45   l->variable_mallocator = xbt_mallocator_new(64,
  46                                               lmm_variable_mallocator_new_f,
  47                                               lmm_variable_mallocator_free_f,
  48                                               lmm_variable_mallocator_reset_f);
  49
  50   return l;
  51 }
  52
  53 void lmm_system_free(lmm_system_t sys)
  54 {
  55   lmm_variable_t var = NULL;
  56   lmm_constraint_t cnst = NULL;
  57
  58   while ((var = extract_variable(sys)))
  59     lmm_var_free(sys, var);
  60
  61   while ((cnst = extract_constraint(sys)))
  62     lmm_cnst_free(sys, cnst);
  63
  64   xbt_mallocator_free(sys->variable_mallocator);
  65   free(sys);
  66 }
  67
  68 void lmm_variable_disable(lmm_system_t sys, lmm_variable_t var)
  69 {
  70   int i;
  71   lmm_element_t elem = NULL;
  72
  73   XBT_IN2("(sys=%p, var=%p)", sys, var);
  74   sys->modified = 1;
  75
  76   for (i = 0; i < var->cnsts_number; i++) {
  77     elem = &var->cnsts[i];
  78     xbt_swag_remove(elem, &(elem->constraint->element_set));
  79     xbt_swag_remove(elem, &(elem->constraint->active_element_set));
  80     if (!xbt_swag_size(&(elem->constraint->element_set)))
  81       make_constraint_inactive(sys, elem->constraint);
  82   }
  83   var->cnsts_number = 0;
  84   XBT_OUT;
  85 }
  86
  87 static void lmm_var_free(lmm_system_t sys, lmm_variable_t var)
  88 {
  89
  90   lmm_variable_disable(sys, var);
  91   free(var->cnsts);
  92   xbt_mallocator_release(sys->variable_mallocator, var);
  93 }
  94
  95 static void lmm_cnst_free(lmm_system_t sys, lmm_constraint_t cnst)
  96 {
  97 /*   xbt_assert0(xbt_swag_size(&(cnst->element_set)), */
  98 /*            "This list should be empty!"); */
  99   remove_active_constraint(sys, cnst);
 100   free(cnst);
 101 }
 102
 103 lmm_constraint_t lmm_constraint_new(lmm_system_t sys, void *id,
 104                                     double bound_value)
 105 {
 106   lmm_constraint_t cnst = NULL;
 107   s_lmm_element_t elem;
 108
 109   cnst = xbt_new0(s_lmm_constraint_t, 1);
 110   cnst->id = id;
 111   xbt_swag_init(&(cnst->element_set),
 112                 xbt_swag_offset(elem, element_set_hookup));
 113   xbt_swag_init(&(cnst->active_element_set),
 114                 xbt_swag_offset(elem, active_element_set_hookup));
 115
 116   cnst->bound = bound_value;
 117   cnst->usage = 0;
 118   cnst->shared = 1;
 119   insert_constraint(sys, cnst);
 120
 121   return cnst;
 122 }
 123
 124 void lmm_constraint_shared(lmm_constraint_t cnst)
 125 {
 126   cnst->shared = 0;
 127 }
 128
 129 int lmm_constraint_is_shared(lmm_constraint_t cnst)
 130 {
 131   return (cnst->shared);
 132 }
 133
 134 void lmm_constraint_free(lmm_system_t sys, lmm_constraint_t cnst)
 135 {
 136   remove_constraint(sys, cnst);
 137   lmm_cnst_free(sys, cnst);
 138 }
 139
 140 static void *lmm_variable_mallocator_new_f(void)
 141 {
 142   return xbt_new(s_lmm_variable_t, 1);
 143 }
 144
 145 static void lmm_variable_mallocator_free_f(void *var)
 146 {
 147   xbt_free(var);
 148 }
 149
 150 static void lmm_variable_mallocator_reset_f(void *var)
 151 {
 152   /* memset to zero like calloc */
 153   memset(var, 0, sizeof(s_lmm_variable_t));
 154 }
 155
 156 lmm_variable_t lmm_variable_new(lmm_system_t sys, void *id,
 157                                 double weight,
 158                                 double bound, int number_of_constraints)
 159 {
 160   lmm_variable_t var = NULL;
 161   int i;
 162
 163   XBT_IN5("(sys=%p, id=%p, weight=%f, bound=%f, num_cons =%d)",
 164           sys, id, weight, bound, number_of_constraints);
 165
 166   var = xbt_mallocator_get(sys->variable_mallocator);
 167   var->id = id;
 168   var->cnsts = xbt_new0(s_lmm_element_t, number_of_constraints);
 169   for (i = 0; i < number_of_constraints; i++) {
 170     /* Should be useless because of the
 171        calloc but it seems to help valgrind... */
 172     var->cnsts[i].element_set_hookup.next = NULL;
 173     var->cnsts[i].element_set_hookup.prev = NULL;
 174     var->cnsts[i].active_element_set_hookup.next = NULL;
 175     var->cnsts[i].active_element_set_hookup.prev = NULL;
 176     var->cnsts[i].constraint = NULL;
 177     var->cnsts[i].variable = NULL;
 178     var->cnsts[i].value = 0.0;
 179   }
 180   var->cnsts_size = number_of_constraints;
 181   var->cnsts_number = 0;        /* Should be useless because of the
 182                                    calloc but it seems to help valgrind... */
 183   var->weight = weight;
 184   var->bound = bound;
 185   var->value = 0.0;
 186   var->df = 0.0;
 187
 188   var->func_f = func_f_def;
 189   var->func_fp = func_fp_def;
 190   var->func_fpi = func_fpi_def;
 191
 192   if (weight)
 193     xbt_swag_insert_at_head(var, &(sys->variable_set));
 194   else
 195     xbt_swag_insert_at_tail(var, &(sys->variable_set));
 196   XBT_OUT;
 197   return var;
 198 }
 199
 200 void lmm_variable_free(lmm_system_t sys, lmm_variable_t var)
 201 {
 202   remove_variable(sys, var);
 203   lmm_var_free(sys, var);
 204 }
 205
 206 double lmm_variable_getvalue(lmm_variable_t var)
 207 {
 208   return (var->value);
 209 }
 210
 211 double lmm_variable_getbound(lmm_variable_t var)
 212 {
 213   return (var->bound);
 214 }
 215
 216 void lmm_expand(lmm_system_t sys, lmm_constraint_t cnst,
 217                 lmm_variable_t var, double value)
 218 {
 219   lmm_element_t elem = NULL;
 220
 221   sys->modified = 1;
 222
 223   xbt_assert0(var->cnsts_number < var->cnsts_size, "Too much constraints");
 224
 225   elem = &(var->cnsts[var->cnsts_number++]);
 226
 227   elem->value = value;
 228   elem->constraint = cnst;
 229   elem->variable = var;
 230
 231   if (var->weight)
 232     xbt_swag_insert_at_head(elem, &(elem->constraint->element_set));
 233   else
 234     xbt_swag_insert_at_tail(elem, &(elem->constraint->element_set));
 235
 236   make_constraint_active(sys, cnst);
 237 }
 238
 239 void lmm_expand_add(lmm_system_t sys, lmm_constraint_t cnst,
 240                     lmm_variable_t var, double value)
 241 {
 242   int i;
 243   sys->modified = 1;
 244
 245   for (i = 0; i < var->cnsts_number; i++)
 246     if (var->cnsts[i].constraint == cnst)
 247       break;
 248
 249   if (i < var->cnsts_number)
 250     var->cnsts[i].value += value;
 251   else
 252     lmm_expand(sys, cnst, var, value);
 253 }
 254
 255 void lmm_elem_set_value(lmm_system_t sys, lmm_constraint_t cnst,
 256                         lmm_variable_t var, double value)
 257 {
 258   int i;
 259
 260   for (i = 0; i < var->cnsts_number; i++)
 261     if (var->cnsts[i].constraint == cnst)
 262       break;
 263
 264   if (i < var->cnsts_number) {
 265     var->cnsts[i].value = value;
 266     sys->modified = 1;
 267   } else
 268     DIE_IMPOSSIBLE;
 269 }
 270
 271 lmm_constraint_t lmm_get_cnst_from_var(lmm_system_t sys,
 272                                        lmm_variable_t var, int num)
 273 {
 274   if (num < var->cnsts_number)
 275     return (var->cnsts[num].constraint);
 276   else
 277     return NULL;
 278 }
 279
 280 int lmm_get_number_of_cnst_from_var(lmm_system_t sys, lmm_variable_t var)
 281 {
 282   return (var->cnsts_number);
 283 }
 284
 285 lmm_variable_t lmm_get_var_from_cnst(lmm_system_t sys,
 286                                      lmm_constraint_t cnst,
 287                                      lmm_element_t * elem)
 288 {
 289   if (!(*elem))
 290     *elem = xbt_swag_getFirst(&(cnst->element_set));
 291   else
 292     *elem = xbt_swag_getNext(*elem, cnst->element_set.offset);
 293   if(*elem)
 294     return (*elem)->variable;
 295   else
 296     return NULL;
 297 }
 298
 299 void *lmm_constraint_id(lmm_constraint_t cnst)
 300 {
 301   return cnst->id;
 302 }
 303
 304 void *lmm_variable_id(lmm_variable_t var)
 305 {
 306   return var->id;
 307 }
 308
 309 static void saturated_constraint_set_update(lmm_system_t sys,
 310                                             lmm_constraint_t cnst,
 311                                             double *min_usage)
 312 {
 313   lmm_constraint_t useless_cnst = NULL;
 314
 315   XBT_IN3("sys=%p, cnst=%p, min_usage=%f", sys, cnst, *min_usage);
 316   if (cnst->usage <= 0) {
 317     XBT_OUT;
 318     return;
 319   }
 320   if (cnst->remaining <= 0) {
 321     XBT_OUT;
 322     return;
 323   }
 324   if ((*min_usage < 0) || (*min_usage > cnst->remaining / cnst->usage)) {
 325     *min_usage = cnst->remaining / cnst->usage;
 326     LOG3(xbt_log_priority_trace,
 327          "min_usage=%f (cnst->remaining=%f, cnst->usage=%f)", *min_usage,
 328          cnst->remaining, cnst->usage);
 329     while ((useless_cnst =
 330             xbt_swag_getFirst(&(sys->saturated_constraint_set))))
 331       xbt_swag_remove(useless_cnst, &(sys->saturated_constraint_set));
 332
 333     xbt_swag_insert(cnst, &(sys->saturated_constraint_set));
 334   } else if (*min_usage == cnst->remaining / cnst->usage) {
 335     xbt_swag_insert(cnst, &(sys->saturated_constraint_set));
 336   }
 337   XBT_OUT;
 338 }
 339
 340 static void saturated_variable_set_update(lmm_system_t sys)
 341 {
 342   lmm_constraint_t cnst = NULL;
 343   xbt_swag_t cnst_list = NULL;
 344   lmm_element_t elem = NULL;
 345   xbt_swag_t elem_list = NULL;
 346
 347   cnst_list = &(sys->saturated_constraint_set);
 348   while ((cnst = xbt_swag_getFirst(cnst_list))) {
 349     elem_list = &(cnst->active_element_set);
 350     xbt_swag_foreach(elem, elem_list) {
 351       if (elem->variable->weight <= 0)
 352         break;
 353       if ((elem->value > 0))
 354         xbt_swag_insert(elem->variable, &(sys->saturated_variable_set));
 355     }
 356     xbt_swag_remove(cnst, cnst_list);
 357   }
 358 }
 359
 360 void lmm_print(lmm_system_t sys)
 361 {
 362   lmm_constraint_t cnst = NULL;
 363   lmm_element_t elem = NULL;
 364   lmm_variable_t var = NULL;
 365   xbt_swag_t cnst_list = NULL;
 366   xbt_swag_t var_list = NULL;
 367   xbt_swag_t elem_list = NULL;
 368   char print_buf[1024];
 369   char *trace_buf = xbt_malloc0(sizeof(char));
 370   double sum = 0.0;
 371
 372   /* Printing Objective */
 373   var_list = &(sys->variable_set);
 374   sprintf(print_buf, "MAX-MIN ( ");
 375   trace_buf =
 376       xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 377   strcat(trace_buf, print_buf);
 378   xbt_swag_foreach(var, var_list) {
 379     sprintf(print_buf, "'%p'(%f) ", var, var->weight);
 380     trace_buf =
 381         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 382     strcat(trace_buf, print_buf);
 383   }
 384   sprintf(print_buf, ")");
 385   trace_buf =
 386       xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 387   strcat(trace_buf, print_buf);
 388   DEBUG1("%s", trace_buf);
 389   trace_buf[0] = '\000';
 390
 391   DEBUG0("Constraints");
 392   /* Printing Constraints */
 393   cnst_list = &(sys->active_constraint_set);
 394   xbt_swag_foreach(cnst, cnst_list) {
 395     sum = 0.0;
 396     elem_list = &(cnst->element_set);
 397     sprintf(print_buf, "\t");
 398     trace_buf =
 399         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 400     strcat(trace_buf, print_buf);
 401     xbt_swag_foreach(elem, elem_list) {
 402       sprintf(print_buf, "%f.'%p'(%f) + ", elem->value,
 403               elem->variable, elem->variable->value);
 404       trace_buf =
 405           xbt_realloc(trace_buf,
 406                       strlen(trace_buf) + strlen(print_buf) + 1);
 407       strcat(trace_buf, print_buf);
 408       sum += elem->value * elem->variable->value;
 409     }
 410     sprintf(print_buf, "0 <= %f ('%p')", cnst->bound, cnst);
 411     trace_buf =
 412         xbt_realloc(trace_buf, strlen(trace_buf) + strlen(print_buf) + 1);
 413     strcat(trace_buf, print_buf);
 414
 415     if (!cnst->shared) {
 416       sprintf(print_buf, " [MAX-Constraint]");
 417       trace_buf =
 418           xbt_realloc(trace_buf,
 419                       strlen(trace_buf) + strlen(print_buf) + 1);
 420       strcat(trace_buf, print_buf);
 421     }
 422     DEBUG1("%s", trace_buf);
 423     trace_buf[0] = '\000';
 424     if (double_positive(sum - cnst->bound))
 425       WARN3("Incorrect value (%f is not smaller than %f): %g",
 426             sum, cnst->bound, sum - cnst->bound);
 427   }
 428
 429   DEBUG0("Variables");
 430   /* Printing Result */
 431   xbt_swag_foreach(var, var_list) {
 432     if (var->bound > 0) {
 433       DEBUG4("'%p'(%f) : %f (<=%f)", var, var->weight, var->value,
 434              var->bound);
 435       if (double_positive(var->value - var->bound))
 436         WARN2("Incorrect value (%f is not smaller than %f",
 437               var->value, var->bound);
 438     } else
 439       DEBUG3("'%p'(%f) : %f", var, var->weight, var->value);
 440   }
 441
 442   free(trace_buf);
 443 }
 444
 445 void lmm_solve(lmm_system_t sys)
 446 {
 447   lmm_variable_t var = NULL;
 448   lmm_constraint_t cnst = NULL;
 449   lmm_element_t elem = NULL;
 450   xbt_swag_t cnst_list = NULL;
 451   xbt_swag_t var_list = NULL;
 452   xbt_swag_t elem_list = NULL;
 453   double min_usage = -1;
 454
 455   if (!(sys->modified))
 456     return;
 457
 458   /* Init */
 459   var_list = &(sys->variable_set);
 460   DEBUG1("Variable set : %d", xbt_swag_size(var_list));
 461   xbt_swag_foreach(var, var_list) {
 462     int nb=0;
 463     int i;
 464     if(var->weight<=0.0) break;
 465     var->value = 0.0;
 466     for (i = 0; i < var->cnsts_number; i++) {
 467       if(var->cnsts[i].value==0.0) nb++;
 468     }
 469     if((nb==var->cnsts_number) && (var->weight>0.0))
 470       var->value = 1.0;
 471   }
 472
 473   /*
 474    * Compute Usage and store the variables that reach the maximum.
 475    */
 476   cnst_list = &(sys->active_constraint_set);
 477   DEBUG1("Active constraints : %d", xbt_swag_size(cnst_list));
 478   xbt_swag_foreach(cnst, cnst_list) {
 479     /* INIT */
 480     cnst->remaining = cnst->bound;
 481     cnst->usage = 0;
 482     elem_list = &(cnst->element_set);
 483     cnst->usage = 0.0;
 484     xbt_swag_foreach(elem, elem_list) {
 485       if (elem->variable->weight <= 0)
 486         break;
 487       if ((elem->value > 0)) {
 488         if (cnst->shared)
 489           cnst->usage += elem->value / elem->variable->weight;
 490         else if (cnst->usage < elem->value / elem->variable->weight)
 491           cnst->usage = elem->value / elem->variable->weight;
 492         DEBUG2("Constraint Usage %p : %f", cnst, cnst->usage);
 493         make_elem_active(elem);
 494       }
 495     }
 496     /* Saturated constraints update */
 497     saturated_constraint_set_update(sys, cnst, &min_usage);
 498   }
 499   saturated_variable_set_update(sys);
 500
 501   /* Saturated variables update */
 502
 503   do {
 504     /* Fix the variables that have to be */
 505     var_list = &(sys->saturated_variable_set);
 506
 507     xbt_swag_foreach(var, var_list) {
 508       if(var->weight<=0.0) DIE_IMPOSSIBLE;
 509       /* First check if some of these variables have reach their upper
 510          bound and update min_usage accordingly. */
 511       DEBUG5
 512           ("var=%p, var->bound=%f, var->weight=%f, min_usage=%f, var->bound*var->weight=%f",
 513            var, var->bound, var->weight, min_usage,
 514            var->bound * var->weight);
 515       if ((var->bound > 0) && (var->bound * var->weight < min_usage)) {
 516         min_usage = var->bound * var->weight;
 517         DEBUG1("Updated min_usage=%f", min_usage);
 518       }
 519     }
 520
 521
 522     while ((var = xbt_swag_getFirst(var_list))) {
 523       int i;
 524
 525       var->value = min_usage / var->weight;
 526       DEBUG5("Min usage: %f, Var(%p)->weight: %f, Var(%p)->value: %f ",
 527              min_usage, var, var->weight, var, var->value);
 528
 529
 530       /* Update usage */
 531
 532       for (i = 0; i < var->cnsts_number; i++) {
 533         elem = &var->cnsts[i];
 534         cnst = elem->constraint;
 535         if (cnst->shared) {
 536           double_update(&(cnst->remaining), elem->value * var->value);
 537           double_update(&(cnst->usage), elem->value / var->weight);
 538           make_elem_inactive(elem);
 539         } else {                /* FIXME one day: We recompute usage.... :( */
 540           cnst->usage = 0.0;
 541           make_elem_inactive(elem);
 542           xbt_swag_foreach(elem, elem_list) {
 543             if (elem->variable->weight <= 0)
 544               break;
 545             if (elem->variable->value > 0)
 546               break;
 547             if ((elem->value > 0)) {
 548               if (cnst->usage < elem->value / elem->variable->weight)
 549                 cnst->usage = elem->value / elem->variable->weight;
 550               DEBUG2("Constraint Usage %p : %f", cnst, cnst->usage);
 551               make_elem_active(elem);
 552             }
 553           }
 554         }
 555       }
 556       xbt_swag_remove(var, var_list);
 557     }
 558
 559     /* Find out which variables reach the maximum */
 560     cnst_list = &(sys->active_constraint_set);
 561     min_usage = -1;
 562     xbt_swag_foreach(cnst, cnst_list) {
 563       saturated_constraint_set_update(sys, cnst, &min_usage);
 564     }
 565     saturated_variable_set_update(sys);
 566
 567   } while (xbt_swag_size(&(sys->saturated_variable_set)));
 568
 569   sys->modified = 0;
 570   if (XBT_LOG_ISENABLED(surf_maxmin, xbt_log_priority_debug)) {
 571     lmm_print(sys);
 572   }
 573 }
 574
 575 /* Not a O(1) function */
 576
 577 void lmm_update(lmm_system_t sys, lmm_constraint_t cnst,
 578                 lmm_variable_t var, double value)
 579 {
 580   int i;
 581
 582   sys->modified = 1;
 583   for (i = 0; i < var->cnsts_number; i++)
 584     if (var->cnsts[i].constraint == cnst) {
 585       var->cnsts[i].value = value;
 586       return;
 587     }
 588 }
 589
 590 /** \brief Attribute the value bound to var->bound.
 591  *
 592  *  \param sys the lmm_system_t
 593  *  \param var the lmm_variable_t
 594  *  \param bound the new bound to associate with var
 595  *
 596  *  Makes var->bound equal to bound. Whenever this function is called
 597  *  a change is  signed in the system. To
 598  *  avoid false system changing detection it is a good idea to test
 599  *  (bound != 0) before calling it.
 600  *
 601  */
 602 void lmm_update_variable_bound(lmm_system_t sys, lmm_variable_t var,
 603                                double bound)
 604 {
 605   sys->modified = 1;
 606   var->bound = bound;
 607 }
 608
 609 /** \brief Add the value delta to var->df (the sum of latencies).
 610  *
 611  *  \param sys the lmm_system_t associated
 612  *  \param var the lmm_variable_t which need to updated
 613  *  \param delta the variation of the latency
 614  *
 615  *  Add the value delta to var->df (the sum of latencys associated to the
 616  *  flow). Whenever this function is called a change is  signed in the system. To
 617  *  avoid false system changing detection it is a good idea to test
 618  *  (delta != 0) before calling it.
 619  *
 620  */
 621 void lmm_update_variable_latency(lmm_system_t sys, lmm_variable_t var,
 622                                  double delta)
 623 {
 624   sys->modified = 1;
 625   var->df += delta;
 626 }
 627
 628 void lmm_update_variable_weight(lmm_system_t sys, lmm_variable_t var,
 629                                 double weight)
 630 {
 631   int i;
 632   lmm_element_t elem;
 633
 634   if(weight==var->weight) return;
 635   XBT_IN3("(sys=%p, var=%p, weight=%f)", sys, var, weight);
 636   sys->modified = 1;
 637   var->weight = weight;
 638   xbt_swag_remove(var, &(sys->variable_set));
 639   if (weight)
 640     xbt_swag_insert_at_head(var, &(sys->variable_set));
 641   else
 642     xbt_swag_insert_at_tail(var, &(sys->variable_set));
 643
 644   for (i = 0; i < var->cnsts_number; i++) {
 645     elem = &var->cnsts[i];
 646     xbt_swag_remove(elem, &(elem->constraint->element_set));
 647     if (weight)
 648       xbt_swag_insert_at_head(elem, &(elem->constraint->element_set));
 649     else
 650       xbt_swag_insert_at_tail(elem, &(elem->constraint->element_set));
 651   }
 652   if(!weight)
 653     var->value = 0.0;
 654
 655   XBT_OUT;
 656 }
 657
 658 double lmm_get_variable_weight(lmm_variable_t var)
 659 {
 660   return var->weight;
 661 }
 662
 663 void lmm_update_constraint_bound(lmm_system_t sys, lmm_constraint_t cnst,
 664                                  double bound)
 665 {
 666   sys->modified = 1;
 667   cnst->bound = bound;
 668 }
 669
 670 int lmm_constraint_used(lmm_system_t sys, lmm_constraint_t cnst)
 671 {
 672   return xbt_swag_belongs(cnst, &(sys->active_constraint_set));
 673 }
 674
 675 lmm_constraint_t lmm_get_first_active_constraint(lmm_system_t sys)
 676 {
 677   return xbt_swag_getFirst(&(sys->active_constraint_set));
 678 }
 679
 680 lmm_constraint_t lmm_get_next_active_constraint(lmm_system_t sys,
 681                                                 lmm_constraint_t cnst)
 682 {
 683   return xbt_swag_getNext(cnst, (sys->active_constraint_set).offset);
 684 }