xref: /petsc/src/ts/event/tsevent.c (revision a6c783d25db86bccc73f5f62db72582ec8c7dead)
1 #include <petsc/private/tsimpl.h> /*I  "petscts.h" I*/
2 
3 #undef __FUNCT__
4 #define __FUNCT__ "TSEventInitialize"
5 /*
6   TSEventInitialize - Initializes TSEvent for TSSolve
7 */
8 PetscErrorCode TSEventInitialize(TSEvent event,TS ts,PetscReal t,Vec U)
9 {
10   PetscErrorCode ierr;
11 
12   PetscFunctionBegin;
13   if (!event) PetscFunctionReturn(0);
14   PetscValidPointer(event,1);
15   PetscValidHeaderSpecific(ts,TS_CLASSID,2);
16   PetscValidHeaderSpecific(U,VEC_CLASSID,4);
17   event->ptime_prev = t;
18   event->iterctr=0;
19   ierr = (*event->eventhandler)(ts,t,U,event->fvalue_prev,event->ctx);CHKERRQ(ierr);
20   /* Initialize the event recorder */
21   event->recorder.ctr = 0;
22   PetscFunctionReturn(0);
23 }
24 
25 #undef __FUNCT__
26 #define __FUNCT__ "TSEventDestroy"
27 PetscErrorCode TSEventDestroy(TSEvent *event)
28 {
29   PetscErrorCode ierr;
30   PetscInt       i;
31 
32   PetscFunctionBegin;
33   PetscValidPointer(event,1);
34   if (!*event) PetscFunctionReturn(0);
35   ierr = PetscFree((*event)->fvalue);CHKERRQ(ierr);
36   ierr = PetscFree((*event)->fvalue_prev);CHKERRQ(ierr);
37   ierr = PetscFree((*event)->fvalue_right);CHKERRQ(ierr);
38   ierr = PetscFree((*event)->zerocrossing);CHKERRQ(ierr);
39   ierr = PetscFree((*event)->side);CHKERRQ(ierr);
40   ierr = PetscFree((*event)->direction);CHKERRQ(ierr);
41   ierr = PetscFree((*event)->terminate);CHKERRQ(ierr);
42   ierr = PetscFree((*event)->events_zero);CHKERRQ(ierr);
43   ierr = PetscFree((*event)->vtol);CHKERRQ(ierr);
44 
45 
46   for (i=0; i < (*event)->recsize; i++) {
47     ierr = PetscFree((*event)->recorder.eventidx[i]);CHKERRQ(ierr);
48   }
49   ierr = PetscFree((*event)->recorder.eventidx);CHKERRQ(ierr);
50   ierr = PetscFree((*event)->recorder.nevents);CHKERRQ(ierr);
51   ierr = PetscFree((*event)->recorder.stepnum);CHKERRQ(ierr);
52   ierr = PetscFree((*event)->recorder.time);CHKERRQ(ierr);
53 
54   ierr = PetscViewerDestroy(&(*event)->monitor);CHKERRQ(ierr);
55   ierr = PetscFree(*event);CHKERRQ(ierr);
56   PetscFunctionReturn(0);
57 }
58 
59 #undef __FUNCT__
60 #define __FUNCT__ "TSSetEventTolerances"
61 /*@
62    TSSetEventTolerances - Set tolerances for event zero crossings when using event handler
63 
64    Logically Collective
65 
66    Input Arguments:
67 +  ts - time integration context
68 .  tol - scalar tolerance, PETSC_DECIDE to leave current value
69 -  vtol - array of tolerances or NULL, used in preference to tol if present
70 
71    Options Database Keys:
72 .  -ts_event_tol <tol> tolerance for event zero crossing
73 
74    Notes:
75    Must call TSSetEventHandler() before setting the tolerances.
76 
77    The size of vtol is equal to the number of events.
78 
79    Level: beginner
80 
81 .seealso: TS, TSEvent, TSSetEventHandler()
82 @*/
83 PetscErrorCode TSSetEventTolerances(TS ts,PetscReal tol,PetscReal vtol[])
84 {
85   TSEvent        event;
86   PetscInt       i;
87 
88   PetscFunctionBegin;
89   PetscValidHeaderSpecific(ts,TS_CLASSID,1);
90   if (vtol) PetscValidRealPointer(vtol,3);
91   if (!ts->event) SETERRQ(PetscObjectComm((PetscObject)ts),PETSC_ERR_USER,"Must set the events first by calling TSSetEventHandler()");
92 
93   event = ts->event;
94   if (vtol) {
95     for (i=0; i < event->nevents; i++) event->vtol[i] = vtol[i];
96   } else {
97     if (tol != PETSC_DECIDE || tol != PETSC_DEFAULT) {
98       for (i=0; i < event->nevents; i++) event->vtol[i] = tol;
99     }
100   }
101   PetscFunctionReturn(0);
102 }
103 
104 #undef __FUNCT__
105 #define __FUNCT__ "TSSetEventHandler"
106 /*@C
107    TSSetEventHandler - Sets a monitoring function used for detecting events
108 
109    Logically Collective on TS
110 
111    Input Parameters:
112 +  ts - the TS context obtained from TSCreate()
113 .  nevents - number of local events
114 .  direction - direction of zero crossing to be detected. -1 => Zero crossing in negative direction,
115                +1 => Zero crossing in positive direction, 0 => both ways (one for each event)
116 .  terminate - flag to indicate whether time stepping should be terminated after
117                event is detected (one for each event)
118 .  eventhandler - event monitoring routine
119 .  postevent - [optional] post-event function
120 -  ctx       - [optional] user-defined context for private data for the
121                event monitor and post event routine (use NULL if no
122                context is desired)
123 
124    Calling sequence of eventhandler:
125    PetscErrorCode EventHandler(TS ts,PetscReal t,Vec U,PetscScalar fvalue[],void* ctx)
126 
127    Input Parameters:
128 +  ts  - the TS context
129 .  t   - current time
130 .  U   - current iterate
131 -  ctx - [optional] context passed with eventhandler
132 
133    Output parameters:
134 .  fvalue    - function value of events at time t
135 
136    Calling sequence of postevent:
137    PetscErrorCode PostEvent(TS ts,PetscInt nevents_zero, PetscInt events_zero[], PetscReal t,Vec U,PetscBool forwardsolve,void* ctx)
138 
139    Input Parameters:
140 +  ts - the TS context
141 .  nevents_zero - number of local events whose event function is zero
142 .  events_zero  - indices of local events which have reached zero
143 .  t            - current time
144 .  U            - current solution
145 .  forwardsolve - Flag to indicate whether TS is doing a forward solve (1) or adjoint solve (0)
146 -  ctx          - the context passed with eventhandler
147 
148    Level: intermediate
149 
150 .keywords: TS, event, set, monitor
151 
152 .seealso: TSCreate(), TSSetTimeStep(), TSSetConvergedReason()
153 @*/
154 PetscErrorCode TSSetEventHandler(TS ts,PetscInt nevents,PetscInt direction[],PetscBool terminate[],PetscErrorCode (*eventhandler)(TS,PetscReal,Vec,PetscScalar[],void*),PetscErrorCode (*postevent)(TS,PetscInt,PetscInt[],PetscReal,Vec,PetscBool,void*),void *ctx)
155 {
156   PetscErrorCode ierr;
157   TSEvent        event;
158   PetscInt       i;
159   PetscBool      flg;
160 #if defined PETSC_USE_REAL_SINGLE
161   PetscReal      tol=1e-4;
162 #else
163   PetscReal      to=1e-6;
164 #endif
165 
166   PetscFunctionBegin;
167   PetscValidHeaderSpecific(ts,TS_CLASSID,1);
168   PetscValidIntPointer(direction,2);
169   PetscValidIntPointer(terminate,3);
170 
171   ierr = PetscNewLog(ts,&event);CHKERRQ(ierr);
172   ierr = PetscMalloc1(nevents,&event->fvalue);CHKERRQ(ierr);
173   ierr = PetscMalloc1(nevents,&event->fvalue_prev);CHKERRQ(ierr);
174   ierr = PetscMalloc1(nevents,&event->fvalue_right);CHKERRQ(ierr);
175   ierr = PetscMalloc1(nevents,&event->zerocrossing);CHKERRQ(ierr);
176   ierr = PetscMalloc1(nevents,&event->side);CHKERRQ(ierr);
177   ierr = PetscMalloc1(nevents,&event->direction);CHKERRQ(ierr);
178   ierr = PetscMalloc1(nevents,&event->terminate);CHKERRQ(ierr);
179   ierr = PetscMalloc1(nevents,&event->vtol);CHKERRQ(ierr);
180   for (i=0; i < nevents; i++) {
181     event->direction[i] = direction[i];
182     event->terminate[i] = terminate[i];
183     event->zerocrossing[i] = PETSC_FALSE;
184     event->side[i] = 0;
185   }
186   ierr = PetscMalloc1(nevents,&event->events_zero);CHKERRQ(ierr);
187   event->nevents = nevents;
188   event->eventhandler = eventhandler;
189   event->postevent = postevent;
190   event->ctx = ctx;
191 
192   event->recsize = 12;  /* Initial size of the recorder */
193   ierr = PetscOptionsBegin(((PetscObject)ts)->comm,"","TS Event options","");CHKERRQ(ierr);
194   {
195     ierr = PetscOptionsReal("-ts_event_tol","Scalar event tolerance for zero crossing check","",tol,&tol,NULL);CHKERRQ(ierr);
196     ierr = PetscOptionsName("-ts_event_monitor","Print choices made by event handler","",&flg);CHKERRQ(ierr);
197     ierr = PetscOptionsInt("-ts_event_recorder_initial_size","Initial size of event recorder","",event->recsize,&event->recsize,NULL);CHKERRQ(ierr);
198   }
199   PetscOptionsEnd();
200 
201   ierr = PetscMalloc1(event->recsize,&event->recorder.time);CHKERRQ(ierr);
202   ierr = PetscMalloc1(event->recsize,&event->recorder.stepnum);CHKERRQ(ierr);
203   ierr = PetscMalloc1(event->recsize,&event->recorder.nevents);CHKERRQ(ierr);
204   ierr = PetscMalloc1(event->recsize,&event->recorder.eventidx);CHKERRQ(ierr);
205   for (i=0; i < event->recsize; i++) {
206     ierr = PetscMalloc1(event->nevents,&event->recorder.eventidx[i]);CHKERRQ(ierr);
207   }
208 
209   for (i=0; i < event->nevents; i++) event->vtol[i] = tol;
210   if (flg) {ierr = PetscViewerASCIIOpen(PETSC_COMM_SELF,"stdout",&event->monitor);CHKERRQ(ierr);}
211 
212   ierr = TSEventDestroy(&ts->event);CHKERRQ(ierr);
213   ts->event = event;
214   PetscFunctionReturn(0);
215 }
216 
217 #undef __FUNCT__
218 #define __FUNCT__ "TSEventRecorderResize"
219 /*
220   TSEventRecorderResize - Resizes (2X) the event recorder arrays whenever the recording limit (event->recsize)
221                           is reached.
222 */
223 PetscErrorCode TSEventRecorderResize(TSEvent event)
224 {
225   PetscErrorCode ierr;
226   PetscReal      *time;
227   PetscInt       *stepnum;
228   PetscInt       *nevents;
229   PetscInt       **eventidx;
230   PetscInt       i,fact=2;
231 
232   PetscFunctionBegin;
233 
234   /* Create large arrays */
235   ierr = PetscMalloc1(fact*event->recsize,&time);CHKERRQ(ierr);
236   ierr = PetscMalloc1(fact*event->recsize,&stepnum);CHKERRQ(ierr);
237   ierr = PetscMalloc1(fact*event->recsize,&nevents);CHKERRQ(ierr);
238   ierr = PetscMalloc1(fact*event->recsize,&eventidx);CHKERRQ(ierr);
239   for (i=0; i < fact*event->recsize; i++) {
240     ierr = PetscMalloc1(event->nevents,&eventidx[i]);CHKERRQ(ierr);
241   }
242 
243   /* Copy over data */
244   ierr = PetscMemcpy(time,event->recorder.time,event->recsize*sizeof(PetscReal));CHKERRQ(ierr);
245   ierr = PetscMemcpy(stepnum,event->recorder.stepnum,event->recsize*sizeof(PetscInt));CHKERRQ(ierr);
246   ierr = PetscMemcpy(nevents,event->recorder.nevents,event->recsize*sizeof(PetscInt));CHKERRQ(ierr);
247   for(i=0; i < event->recsize; i++) {
248     ierr = PetscMemcpy(eventidx[i],event->recorder.eventidx[i],event->recorder.nevents[i]*sizeof(PetscInt));CHKERRQ(ierr);
249   }
250 
251   /* Destroy old arrays */
252   for (i=0; i < event->recsize; i++) {
253     ierr = PetscFree(event->recorder.eventidx[i]);CHKERRQ(ierr);
254   }
255   ierr = PetscFree(event->recorder.eventidx);CHKERRQ(ierr);
256   ierr = PetscFree(event->recorder.nevents);CHKERRQ(ierr);
257   ierr = PetscFree(event->recorder.stepnum);CHKERRQ(ierr);
258   ierr = PetscFree(event->recorder.time);CHKERRQ(ierr);
259 
260   /* Set pointers */
261   event->recorder.time = time;
262   event->recorder.stepnum = stepnum;
263   event->recorder.nevents = nevents;
264   event->recorder.eventidx = eventidx;
265 
266   /* Double size */
267   event->recsize *= fact;
268 
269   PetscFunctionReturn(0);
270 }
271 
272 /*
273    Helper rutine to handle user postenvents and recording
274 */
275 #undef __FUNCT__
276 #define __FUNCT__ "TSPostEvent"
277 static PetscErrorCode TSPostEvent(TS ts,PetscReal t,Vec U)
278 {
279   PetscErrorCode ierr;
280   TSEvent        event = ts->event;
281   PetscBool      terminate = PETSC_FALSE;
282   PetscInt       i,ctr,stepnum;
283   PetscBool      ts_terminate;
284   PetscBool      forwardsolve = PETSC_TRUE; /* Flag indicating that TS is doing a forward solve */
285 
286   PetscFunctionBegin;
287   if (event->postevent) {
288     ierr = (*event->postevent)(ts,event->nevents_zero,event->events_zero,t,U,forwardsolve,event->ctx);CHKERRQ(ierr);
289   }
290 
291   /* Handle termination events */
292   for (i=0; i < event->nevents_zero; i++) {
293     terminate = (PetscBool)(terminate || event->terminate[event->events_zero[i]]);
294   }
295   ierr = MPIU_Allreduce(&terminate,&ts_terminate,1,MPIU_BOOL,MPI_LOR,((PetscObject)ts)->comm);CHKERRQ(ierr);
296   if (ts_terminate) {
297     ierr = TSSetConvergedReason(ts,TS_CONVERGED_EVENT);CHKERRQ(ierr);
298     event->status = TSEVENT_NONE;
299   } else {
300     event->status = TSEVENT_RESET_NEXTSTEP;
301   }
302 
303   event->ptime_prev = t;
304   /* Reset event residual functions as states might get changed by the postevent callback */
305   if (event->postevent) {ierr = (*event->eventhandler)(ts,t,U,event->fvalue,event->ctx);CHKERRQ(ierr);}
306   /* Cache current event residual functions */
307   for (i=0; i < event->nevents; i++) event->fvalue_prev[i] = event->fvalue[i];
308 
309   /* Record the event in the event recorder */
310   ierr = TSGetTimeStepNumber(ts,&stepnum);CHKERRQ(ierr);
311   ctr = event->recorder.ctr;
312   if (ctr == event->recsize) {
313     ierr = TSEventRecorderResize(event);CHKERRQ(ierr);
314   }
315   event->recorder.time[ctr] = t;
316   event->recorder.stepnum[ctr] = stepnum;
317   event->recorder.nevents[ctr] = event->nevents_zero;
318   for (i=0; i < event->nevents_zero; i++) event->recorder.eventidx[ctr][i] = event->events_zero[i];
319   event->recorder.ctr++;
320   PetscFunctionReturn(0);
321 }
322 
323 /* Uses Anderson-Bjorck variant of regular falsi method */
324 PETSC_STATIC_INLINE PetscReal TSEventComputeStepSize(PetscReal tleft,PetscReal t, PetscReal tright, PetscScalar fleft, PetscScalar f, PetscScalar fright, PetscInt side,PetscReal dt)
325 {
326   PetscReal scal=1.0;
327   if(PetscRealPart(fleft)*PetscRealPart(f) < 0) {
328     if(side == 1) {
329       scal = (PetscRealPart(fright) - PetscRealPart(f))/PetscRealPart(fright);
330       if(scal < PETSC_SMALL) scal = 0.5;
331     }
332     dt = PetscMin(dt,(scal*PetscRealPart(fleft)*t - PetscRealPart(f)*tleft)/(scal*PetscRealPart(fleft) - PetscRealPart(f)) - tleft);
333   } else {
334     if(side == -1) {
335       scal = (PetscRealPart(fleft) - PetscRealPart(f))/PetscRealPart(fleft);
336       if(scal < PETSC_SMALL) scal = 0.5;
337     }
338     dt = PetscMin(dt,(PetscRealPart(f)*tright - scal*PetscRealPart(fright)*t)/(PetscRealPart(f) - scal*PetscRealPart(fright)) - t);
339   }
340   return dt;
341 }
342 
343 
344 #undef __FUNCT__
345 #define __FUNCT__ "TSEventHandler"
346 PetscErrorCode TSEventHandler(TS ts)
347 {
348   PetscErrorCode ierr;
349   TSEvent        event;
350   PetscReal      t;
351   Vec            U;
352   PetscInt       i;
353   PetscReal      dt,dt_min;
354   PetscInt       rollback=0,in[2],out[2];
355   PetscInt       fvalue_sign,fvalueprev_sign;
356 
357   PetscFunctionBegin;
358   PetscValidHeaderSpecific(ts,TS_CLASSID,1);
359   if (!ts->event) PetscFunctionReturn(0);
360   event = ts->event;
361 
362   ierr = TSGetTime(ts,&t);CHKERRQ(ierr);
363   ierr = TSGetTimeStep(ts,&dt);CHKERRQ(ierr);
364   ierr = TSGetSolution(ts,&U);CHKERRQ(ierr);
365 
366   if (event->status == TSEVENT_NONE) {
367     event->timestep_prev = dt;
368   }
369 
370   if (event->status == TSEVENT_RESET_NEXTSTEP) {
371     /* Restore previous time step */
372     dt = event->timestep_prev;
373     ierr = TSSetTimeStep(ts,dt);CHKERRQ(ierr);
374     event->status = TSEVENT_NONE;
375   }
376 
377   if (event->status == TSEVENT_NONE) {
378     event->ptime_end = t;
379   }
380 
381   ierr = (*event->eventhandler)(ts,t,U,event->fvalue,event->ctx);CHKERRQ(ierr);
382 
383   for (i=0; i < event->nevents; i++) {
384     if (PetscAbsScalar(event->fvalue[i]) < event->vtol[i]) {
385       event->status = TSEVENT_ZERO;
386       event->fvalue_right[i] = event->fvalue[i];
387       continue;
388     }
389     fvalue_sign = PetscSign(PetscRealPart(event->fvalue[i]));
390     fvalueprev_sign = PetscSign(PetscRealPart(event->fvalue_prev[i]));
391     if (fvalueprev_sign != 0 && (fvalue_sign != fvalueprev_sign) && (PetscAbsScalar(event->fvalue_prev[i]) > event->vtol[i])) {
392       switch (event->direction[i]) {
393       case -1:
394         if (fvalue_sign < 0) {
395 	  rollback = 1;
396 
397 	  /* Compute new time step */
398 	  dt = TSEventComputeStepSize(event->ptime_prev,t,event->ptime_right,event->fvalue_prev[i],event->fvalue[i],event->fvalue_right[i],event->side[i],dt);
399 
400 	  if (event->monitor) {
401 	    ierr = PetscViewerASCIIPrintf(event->monitor,"TSEvent: iter %D - Event %D interval detected [%g - %g]\n",event->iterctr,i,(double)event->ptime_prev,(double)t);CHKERRQ(ierr);
402 	  }
403 	  event->fvalue_right[i] = event->fvalue[i];
404 	  event->side[i] = 1;
405 
406 	  if(!event->iterctr) event->zerocrossing[i] = PETSC_TRUE;
407 	  event->status = TSEVENT_LOCATED_INTERVAL;
408         }
409         break;
410       case 1:
411         if (fvalue_sign > 0) {
412 	  rollback = 1;
413 
414  	  /* Compute new time step */
415 	  dt = TSEventComputeStepSize(event->ptime_prev,t,event->ptime_right,event->fvalue_prev[i],event->fvalue[i],event->fvalue_right[i],event->side[i],dt);
416 
417 	  if (event->monitor) {
418 	    ierr = PetscViewerASCIIPrintf(event->monitor,"TSEvent: iter %D - Event %D interval detected [%g - %g]\n",event->iterctr,i,(double)event->ptime_prev,(double)t);CHKERRQ(ierr);
419 	  }
420 	  event->fvalue_right[i] = event->fvalue[i];
421 	  event->side[i] = 1;
422 
423      	  if(!event->iterctr) event->zerocrossing[i] = PETSC_TRUE;
424 	  event->status = TSEVENT_LOCATED_INTERVAL;
425         }
426         break;
427       case 0:
428 	rollback = 1;
429 
430 	/* Compute new time step */
431 	dt = TSEventComputeStepSize(event->ptime_prev,t,event->ptime_right,event->fvalue_prev[i],event->fvalue[i],event->fvalue_right[i],event->side[i],dt);
432 
433 	if (event->monitor) {
434 	  ierr = PetscViewerASCIIPrintf(event->monitor,"TSEvent: iter %D - Event %D interval detected [%g - %g]\n",event->iterctr,i,(double)event->ptime_prev,(double)t);CHKERRQ(ierr);
435 	}
436 	event->fvalue_right[i] = event->fvalue[i];
437 	event->side[i] = 1;
438 
439 	if(!event->iterctr) event->zerocrossing[i] = PETSC_TRUE;
440 	event->status = TSEVENT_LOCATED_INTERVAL;
441 
442         break;
443       }
444     }
445   }
446 
447   in[0] = event->status; in[1] = rollback;
448   ierr = MPIU_Allreduce(in,out,2,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)ts));CHKERRQ(ierr);
449   event->status = (TSEventStatus)out[0]; rollback = out[1];
450   if (rollback) event->status = TSEVENT_LOCATED_INTERVAL;
451 
452   event->nevents_zero = 0;
453   if (event->status == TSEVENT_ZERO) {
454     for (i=0; i < event->nevents; i++) {
455       if (PetscAbsScalar(event->fvalue[i]) < event->vtol[i]) {
456         event->events_zero[event->nevents_zero++] = i;
457         if (event->monitor) {
458           ierr = PetscViewerASCIIPrintf(event->monitor,"TSEvent: Event %D zero crossing at time %g located in %D iterations\n",i,(double)t,event->iterctr);CHKERRQ(ierr);
459         }
460 	event->zerocrossing[i] = PETSC_FALSE;
461       }
462       event->side[i] = 0;
463     }
464     ierr = TSPostEvent(ts,t,U);CHKERRQ(ierr);
465 
466     dt = event->ptime_end - t;
467     if (PetscAbsReal(dt) < PETSC_SMALL) dt += event->timestep_prev; /* XXX Should be done better */
468     ierr = TSSetTimeStep(ts,dt);CHKERRQ(ierr);
469     event->iterctr = 0;
470     PetscFunctionReturn(0);
471   }
472 
473   if (event->status == TSEVENT_LOCATED_INTERVAL) {
474     ierr = TSRollBack(ts);CHKERRQ(ierr);
475     ts->steps--;
476     ts->total_steps--;
477     ierr = TSSetConvergedReason(ts,TS_CONVERGED_ITERATING);CHKERRQ(ierr);
478     event->status = TSEVENT_PROCESSING;
479 
480     event->ptime_right = t;
481   } else {
482     for(i=0; i < event->nevents; i++) {
483       if (event->status == TSEVENT_PROCESSING && event->zerocrossing[i]) {
484 	/* Compute new time step */
485 	dt = TSEventComputeStepSize(event->ptime_prev,t,event->ptime_right,event->fvalue_prev[i],event->fvalue[i],event->fvalue_right[i],event->side[i],dt);
486 
487 	event->side[i] = -1;
488       }
489       event->fvalue_prev[i] = event->fvalue[i];
490     }
491 
492     if (event->monitor && event->status == TSEVENT_PROCESSING) {
493       ierr = PetscViewerASCIIPrintf(event->monitor,"TSEvent: iter %D - Stepping forward as no event detected in interval [%g - %g]\n",event->iterctr,(double)event->ptime_prev,(double)t);CHKERRQ(ierr);
494     }
495     event->ptime_prev = t;
496   }
497 
498   if(event->status == TSEVENT_PROCESSING) event->iterctr++;
499 
500   ierr = MPIU_Allreduce(&dt,&dt_min,1,MPIU_REAL,MPIU_MIN,PetscObjectComm((PetscObject)ts));CHKERRQ(ierr);
501   ierr = TSSetTimeStep(ts,dt_min);CHKERRQ(ierr);
502   PetscFunctionReturn(0);
503 }
504 
505 #undef __FUNCT__
506 #define __FUNCT__ "TSAdjointEventHandler"
507 PetscErrorCode TSAdjointEventHandler(TS ts)
508 {
509   PetscErrorCode ierr;
510   TSEvent        event;
511   PetscReal      t;
512   Vec            U;
513   PetscInt       ctr;
514   PetscBool      forwardsolve=PETSC_FALSE; /* Flag indicating that TS is doing an adjoint solve */
515 
516   PetscFunctionBegin;
517   PetscValidHeaderSpecific(ts,TS_CLASSID,1);
518   if (!ts->event) PetscFunctionReturn(0);
519   event = ts->event;
520 
521   ierr = TSGetTime(ts,&t);CHKERRQ(ierr);
522   ierr = TSGetSolution(ts,&U);CHKERRQ(ierr);
523 
524   ctr = event->recorder.ctr-1;
525   if (ctr >= 0 && PetscAbsReal(t - event->recorder.time[ctr]) < PETSC_SMALL) {
526     /* Call the user postevent function */
527     if (event->postevent) {
528       ierr = (*event->postevent)(ts,event->recorder.nevents[ctr],event->recorder.eventidx[ctr],t,U,forwardsolve,event->ctx);CHKERRQ(ierr);
529       event->recorder.ctr--;
530     }
531   }
532 
533   PetscBarrier((PetscObject)ts);
534   PetscFunctionReturn(0);
535 }
536