Actual source code: ex41.c

petsc-3.13.3 2020-07-01
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  1: static char help[] = "Parallel bouncing ball example to test TS event feature.\n";

  3: /*
  4:   The dynamics of the bouncing ball is described by the ODE
  5:                   u1_t = u2
  6:                   u2_t = -9.8

  8:   Each processor is assigned one ball.

 10:   The event function routine checks for the ball hitting the
 11:   ground (u1 = 0). Every time the ball hits the ground, its velocity u2 is attenuated by
 12:   a factor of 0.9 and its height set to 1.0*rank.
 13: */

 15:  #include <petscts.h>

 17: PetscErrorCode EventFunction(TS ts,PetscReal t,Vec U,PetscScalar *fvalue,void *ctx)
 18: {
 19:   PetscErrorCode    ierr;
 20:   const PetscScalar *u;

 23:   /* Event for ball height */
 24:   VecGetArrayRead(U,&u);
 25:   fvalue[0] = u[0];
 26:   VecRestoreArrayRead(U,&u);
 27:   return(0);
 28: }

 30: PetscErrorCode PostEventFunction(TS ts,PetscInt nevents,PetscInt event_list[],PetscReal t,Vec U,PetscBool forwardsolve,void* ctx)
 31: {
 33:   PetscScalar    *u;
 34:   PetscMPIInt    rank;

 37:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 38:   if (nevents) {
 39:     PetscPrintf(PETSC_COMM_SELF,"Ball hit the ground at t = %5.2f seconds -> Processor[%d]\n",(double)t,rank);
 40:     /* Set new initial conditions with .9 attenuation */
 41:     VecGetArray(U,&u);
 42:     u[0] =  1.0*rank;
 43:     u[1] = -0.9*u[1];
 44:     VecRestoreArray(U,&u);
 45:   }
 46:   return(0);
 47: }

 49: /*
 50:      Defines the ODE passed to the ODE solver in explicit form: U_t = F(U)
 51: */
 52: static PetscErrorCode RHSFunction(TS ts,PetscReal t,Vec U,Vec F,void *ctx)
 53: {
 54:   PetscErrorCode    ierr;
 55:   PetscScalar       *f;
 56:   const PetscScalar *u;

 59:   /*  The next three lines allow us to access the entries of the vectors directly */
 60:   VecGetArrayRead(U,&u);
 61:   VecGetArray(F,&f);

 63:   f[0] = u[1];
 64:   f[1] = - 9.8;

 66:   VecRestoreArrayRead(U,&u);
 67:   VecRestoreArray(F,&f);
 68:   return(0);
 69: }

 71: /*
 72:      Defines the Jacobian of the ODE passed to the ODE solver. See TSSetRHSJacobian() for the meaning the Jacobian.
 73: */
 74: static PetscErrorCode RHSJacobian(TS ts,PetscReal t,Vec U,Mat A,Mat B,void *ctx)
 75: {
 76:   PetscErrorCode    ierr;
 77:   PetscInt          rowcol[2],rstart;
 78:   PetscScalar       J[2][2];
 79:   const PetscScalar *u;

 82:   VecGetArrayRead(U,&u);

 84:   MatGetOwnershipRange(B,&rstart,NULL);
 85:   rowcol[0] = rstart; rowcol[1] = rstart+1;

 87:   J[0][0] = 0.0;      J[0][1] = 1.0;
 88:   J[1][0] = 0.0;      J[1][1] = 0.0;
 89:   MatSetValues(B,2,rowcol,2,rowcol,&J[0][0],INSERT_VALUES);

 91:   VecRestoreArrayRead(U,&u);
 92:   MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
 93:   MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
 94:   if (A != B) {
 95:     MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 96:     MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
 97:   }
 98:   return(0);
 99: }

101: /*
102:      Defines the ODE passed to the ODE solver in implicit form: F(U_t,U) = 0
103: */
104: static PetscErrorCode IFunction(TS ts,PetscReal t,Vec U,Vec Udot,Vec F,void *ctx)
105: {
106:   PetscErrorCode    ierr;
107:   PetscScalar       *f;
108:   const PetscScalar *u,*udot;

111:   /*  The next three lines allow us to access the entries of the vectors directly */
112:   VecGetArrayRead(U,&u);
113:   VecGetArrayRead(Udot,&udot);
114:   VecGetArray(F,&f);

116:   f[0] = udot[0] - u[1];
117:   f[1] = udot[1] + 9.8;

119:   VecRestoreArrayRead(U,&u);
120:   VecRestoreArrayRead(Udot,&udot);
121:   VecRestoreArray(F,&f);
122:   return(0);
123: }

125: /*
126:      Defines the Jacobian of the ODE passed to the ODE solver. See TSSetIJacobian() for the meaning of a and the Jacobian.
127: */
128: static PetscErrorCode IJacobian(TS ts,PetscReal t,Vec U,Vec Udot,PetscReal a,Mat A,Mat B,void *ctx)
129: {
130:   PetscErrorCode    ierr;
131:   PetscInt          rowcol[2],rstart;
132:   PetscScalar       J[2][2];
133:   const PetscScalar *u,*udot;

136:   VecGetArrayRead(U,&u);
137:   VecGetArrayRead(Udot,&udot);

139:   MatGetOwnershipRange(B,&rstart,NULL);
140:   rowcol[0] = rstart; rowcol[1] = rstart+1;

142:   J[0][0] = a;        J[0][1] = -1.0;
143:   J[1][0] = 0.0;      J[1][1] = a;
144:   MatSetValues(B,2,rowcol,2,rowcol,&J[0][0],INSERT_VALUES);

146:   VecRestoreArrayRead(U,&u);
147:   VecRestoreArrayRead(Udot,&udot);

149:   MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
150:   MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
151:   if (A != B) {
152:     MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
153:     MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
154:   }
155:   return(0);
156: }

158: int main(int argc,char **argv)
159: {
160:   TS             ts;            /* ODE integrator */
161:   Vec            U;             /* solution will be stored here */
163:   PetscMPIInt    rank;
164:   PetscInt       n = 2;
165:   PetscScalar    *u;
166:   PetscInt       direction=-1;
167:   PetscBool      terminate=PETSC_FALSE;
168:   PetscBool      rhs_form=PETSC_FALSE,hist=PETSC_TRUE;
169:   TSAdapt        adapt;

171:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
172:      Initialize program
173:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
174:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
175:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

177:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
178:      Create timestepping solver context
179:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
180:   TSCreate(PETSC_COMM_WORLD,&ts);
181:   TSSetType(ts,TSROSW);

183:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
184:      Set ODE routines
185:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
186:   TSSetProblemType(ts,TS_NONLINEAR);
187:   /* Users are advised against the following branching and code duplication.
188:      For problems without a mass matrix like the one at hand, the RHSFunction
189:      (and companion RHSJacobian) interface is enough to support both explicit
190:      and implicit timesteppers. This tutorial example also deals with the
191:      IFunction/IJacobian interface for demonstration and testing purposes. */
192:   PetscOptionsGetBool(NULL,NULL,"-rhs-form",&rhs_form,NULL);
193:   if (rhs_form) {
194:     TSSetRHSFunction(ts,NULL,RHSFunction,NULL);
195:     TSSetRHSJacobian(ts,NULL,NULL,RHSJacobian,NULL);
196:   } else {
197:     TSSetIFunction(ts,NULL,IFunction,NULL);
198:     TSSetIJacobian(ts,NULL,NULL,IJacobian,NULL);
199:   }

201:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
202:      Set initial conditions
203:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
204:   VecCreate(PETSC_COMM_WORLD,&U);
205:   VecSetSizes(U,n,PETSC_DETERMINE);
206:   VecSetUp(U);
207:   VecGetArray(U,&u);
208:   u[0] = 1.0*rank;
209:   u[1] = 20.0;
210:   VecRestoreArray(U,&u);
211:   TSSetSolution(ts,U);

213:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
214:      Set solver options
215:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
216:   TSSetSaveTrajectory(ts);
217:   TSSetMaxTime(ts,30.0);
218:   TSSetExactFinalTime(ts,TS_EXACTFINALTIME_STEPOVER);
219:   TSSetTimeStep(ts,0.1);
220:   /* The adapative time step controller could take very large timesteps resulting in
221:      the same event occuring multiple times in the same interval. A maximum step size
222:      limit is enforced here to avoid this issue. */
223:   TSGetAdapt(ts,&adapt);
224:   TSAdaptSetType(adapt,TSADAPTBASIC);
225:   TSAdaptSetStepLimits(adapt,0.0,0.5);

227:   /* Set direction and terminate flag for the event */
228:   TSSetEventHandler(ts,1,&direction,&terminate,EventFunction,PostEventFunction,NULL);

230:   TSSetFromOptions(ts);

232:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
233:      Run timestepping solver
234:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
235:   TSSolve(ts,U);

237:   if (hist) { /* replay following history */
238:     TSTrajectory tj;
239:     PetscReal    tf,t0,dt;

241:     TSGetTime(ts,&tf);
242:     TSSetMaxTime(ts,tf);
243:     TSSetStepNumber(ts,0);
244:     TSRestartStep(ts);
245:     TSSetExactFinalTime(ts,TS_EXACTFINALTIME_MATCHSTEP);
246:     TSSetFromOptions(ts);
247:     TSSetEventHandler(ts,1,&direction,&terminate,EventFunction,PostEventFunction,NULL);
248:     TSGetAdapt(ts,&adapt);
249:     TSAdaptSetType(adapt,TSADAPTHISTORY);
250:     TSGetTrajectory(ts,&tj);
251:     TSAdaptHistorySetTrajectory(adapt,tj,PETSC_FALSE);
252:     TSAdaptHistoryGetStep(adapt,0,&t0,&dt);
253:     /* this example fails with single (or smaller) precision */
254: #if defined(PETSC_USE_REAL_SINGLE) || defined(PETSC_USE_REAL__FP16)
255:     TSAdaptSetType(adapt,TSADAPTBASIC);
256:     TSAdaptSetStepLimits(adapt,0.0,0.5);
257:     TSSetFromOptions(ts);
258: #endif
259:     TSSetTime(ts,t0);
260:     TSSetTimeStep(ts,dt);
261:     TSResetTrajectory(ts);
262:     VecGetArray(U,&u);
263:     u[0] = 1.0*rank;
264:     u[1] = 20.0;
265:     VecRestoreArray(U,&u);
266:     TSSolve(ts,U);
267:   }
268:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
269:      Free work space.  All PETSc objects should be destroyed when they are no longer needed.
270:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
271:   VecDestroy(&U);
272:   TSDestroy(&ts);

274:   PetscFinalize();
275:   return ierr;
276: }

278: /*TEST

280:    test:
281:       suffix: a
282:       nsize: 2
283:       args: -ts_trajectory_type memory -snes_stol 1e-4
284:       filter: sort -b

286:    test:
287:       suffix: b
288:       nsize: 2
289:       args: -ts_trajectory_type memory -ts_type arkimex -snes_stol 1e-4
290:       filter: sort -b

292:    test:
293:       suffix: c
294:       nsize: 2
295:       args: -ts_trajectory_type memory -ts_type theta -ts_adapt_type basic -ts_atol 1e-1 -snes_stol 1e-4
296:       filter: sort -b

298:    test:
299:       suffix: d
300:       nsize: 2
301:       args: -ts_trajectory_type memory -ts_type alpha -ts_adapt_type basic -ts_atol 1e-1 -snes_stol 1e-4
302:       filter: sort -b

304:    test:
305:       suffix: e
306:       nsize: 2
307:       args: -ts_trajectory_type memory -ts_type bdf -ts_adapt_dt_max 0.015 -ts_max_steps 3000
308:       filter: sort -b

310:    test:
311:       suffix: f
312:       nsize: 2
313:       args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 3bs
314:       filter: sort -b

316:    test:
317:       suffix: g
318:       nsize: 2
319:       args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 5bs
320:       filter: sort -b

322:    test:
323:       suffix: h
324:       nsize: 2
325:       args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 6vr
326:       filter: sort -b
327:       output_file: output/ex41_g.out

329:    test:
330:       suffix: i
331:       nsize: 2
332:       args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 7vr
333:       filter: sort -b
334:       output_file: output/ex41_g.out

336:    test:
337:       suffix: j
338:       nsize: 2
339:       args: -ts_trajectory_type memory -rhs-form -ts_type rk -ts_rk_type 8vr
340:       filter: sort -b
341:       output_file: output/ex41_g.out

343: TEST*/