Actual source code: ex40.c

petsc-3.7.2 2016-06-05
Report Typos and Errors
  1: static char help[] = "Serial 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:   There are two events set in this example. The first one checks for the ball hitting the
  9:   ground (u1 = 0). Every time the ball hits the ground, its velocity u2 is attenuated by
 10:   a factor of 0.9. The second event sets a limit on the number of ball bounces.
 11: */

 13: #include <petscts.h>

 15: typedef struct {
 16:   PetscInt maxbounces;
 17:   PetscInt nbounces;
 18: } AppCtx;

 22: PetscErrorCode EventFunction(TS ts,PetscReal t,Vec U,PetscScalar *fvalue,void *ctx)
 23: {
 24:   AppCtx            *app=(AppCtx*)ctx;
 25:   PetscErrorCode    ierr;
 26:   const PetscScalar *u;

 29:   /* Event for ball height */
 30:   VecGetArrayRead(U,&u);
 31:   fvalue[0] = u[0];
 32:   /* Event for number of bounces */
 33:   fvalue[1] = app->maxbounces - app->nbounces;
 34:   VecRestoreArrayRead(U,&u);
 35:   return(0);
 36: }

 40: PetscErrorCode PostEventFunction(TS ts,PetscInt nevents,PetscInt event_list[],PetscReal t,Vec U,PetscBool forwardsolve,void* ctx)
 41: {
 42:   AppCtx         *app=(AppCtx*)ctx;
 44:   PetscScalar    *u;

 47:   if (event_list[0] == 0) {
 48:     PetscPrintf(PETSC_COMM_SELF,"Ball hit the ground at t = %5.2f seconds\n",(double)t);
 49:     /* Set new initial conditions with .9 attenuation */
 50:     VecGetArray(U,&u);
 51:     u[0] =  0.0;
 52:     u[1] = -0.9*u[1];
 53:     VecRestoreArray(U,&u);
 54:   } else if (event_list[0] == 1) {
 55:     PetscPrintf(PETSC_COMM_SELF,"Ball bounced %D times\n",app->nbounces);
 56:   }
 57:   app->nbounces++;
 58:   return(0);
 59: }

 63: /*
 64:      Defines the ODE passed to the ODE solver
 65: */
 66: static PetscErrorCode IFunction(TS ts,PetscReal t,Vec U,Vec Udot,Vec F,void *ctx)
 67: {
 68:   PetscErrorCode    ierr;
 69:   PetscScalar       *f;
 70:   const PetscScalar *u,*udot;

 73:   /*  The next three lines allow us to access the entries of the vectors directly */
 74:   VecGetArrayRead(U,&u);
 75:   VecGetArrayRead(Udot,&udot);
 76:   VecGetArray(F,&f);

 78:   f[0] = udot[0] - u[1];
 79:   f[1] = udot[1] + 9.8;

 81:   VecRestoreArrayRead(U,&u);
 82:   VecRestoreArrayRead(Udot,&udot);
 83:   VecRestoreArray(F,&f);
 84:   return(0);
 85: }

 89: /*
 90:      Defines the Jacobian of the ODE passed to the ODE solver. See TSSetIJacobian() for the meaning of a and the Jacobian.
 91: */
 92: static PetscErrorCode IJacobian(TS ts,PetscReal t,Vec U,Vec Udot,PetscReal a,Mat A,Mat B,void *ctx)
 93: {
 94:   PetscErrorCode    ierr;
 95:   PetscInt          rowcol[] = {0,1};
 96:   PetscScalar       J[2][2];
 97:   const PetscScalar *u,*udot;

100:   VecGetArrayRead(U,&u);
101:   VecGetArrayRead(Udot,&udot);

103:   J[0][0] = a;                       J[0][1] = -1;
104:   J[1][0] = 0.0;                     J[1][1] = a;
105:   MatSetValues(B,2,rowcol,2,rowcol,&J[0][0],INSERT_VALUES);

107:   VecRestoreArrayRead(U,&u);
108:   VecRestoreArrayRead(Udot,&udot);

110:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
111:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
112:   if (A != B) {
113:     MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
114:     MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
115:   }
116:   return(0);
117: }

121: int main(int argc,char **argv)
122: {
123:   TS             ts;            /* ODE integrator */
124:   Vec            U;             /* solution will be stored here */
125:   Mat            A;             /* Jacobian matrix */
127:   PetscMPIInt    size;
128:   PetscInt       n = 2;
129:   PetscScalar    *u;
130:   AppCtx         app;
131:   PetscInt       direction[2];
132:   PetscBool      terminate[2];
133:   TSAdapt        adapt;

135:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
136:      Initialize program
137:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
138:   PetscInitialize(&argc,&argv,(char*)0,help);
139:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
140:   if (size > 1) SETERRQ(PETSC_COMM_WORLD,PETSC_ERR_SUP,"Only for sequential runs");

142:   app.nbounces = 0;
143:   app.maxbounces = 10;
144:   PetscOptionsBegin(PETSC_COMM_WORLD,NULL,"ex21 options","");
145:   PetscOptionsInt("-maxbounces","","",app.maxbounces,&app.maxbounces,NULL);
146:   PetscOptionsEnd();

148:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
149:     Create necessary matrix and vectors
150:     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
151:   MatCreate(PETSC_COMM_WORLD,&A);
152:   MatSetSizes(A,n,n,PETSC_DETERMINE,PETSC_DETERMINE);
153:   MatSetType(A,MATDENSE);
154:   MatSetFromOptions(A);
155:   MatSetUp(A);

157:   MatCreateVecs(A,&U,NULL);

159:   VecGetArray(U,&u);
160:   u[0] = 0.0;
161:   u[1] = 20.0;
162:   VecRestoreArray(U,&u);

164:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
165:      Create timestepping solver context
166:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
167:   TSCreate(PETSC_COMM_WORLD,&ts);
168:   TSSetSaveTrajectory(ts);
169:   TSSetProblemType(ts,TS_NONLINEAR);
170:   TSSetType(ts,TSROSW);
171:   TSSetIFunction(ts,NULL,(TSIFunction) IFunction,NULL);
172:   TSSetIJacobian(ts,A,A,(TSIJacobian)IJacobian,NULL);

174:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
175:      Set initial conditions
176:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
177:   TSSetSolution(ts,U);

179:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
180:      Set solver options
181:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
182:   TSSetDuration(ts,1000,30.0);
183:   TSSetExactFinalTime(ts,TS_EXACTFINALTIME_STEPOVER);
184:   TSSetInitialTimeStep(ts,0.0,0.1);
185:   TSSetFromOptions(ts);

187:   /* Set directions and terminate flags for the two events */
188:   direction[0] = -1;            direction[1] = -1;
189:   terminate[0] = PETSC_FALSE;   terminate[1] = PETSC_TRUE;
190:   TSSetEventHandler(ts,2,direction,terminate,EventFunction,PostEventFunction,(void*)&app);

192:   /* The adapative time step controller could take very large timesteps resulting in
193:      the same event occuring multiple times in the same interval. A maximum step size
194:      limit is enforced here to avoid this issue.
195:   */
196:   TSGetAdapt(ts,&adapt);
197:   TSAdaptSetStepLimits(adapt,0.0,0.5);

199:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
200:      Run timestepping solver
201:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
202:   TSSolve(ts,U);

204:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
205:      Free work space.  All PETSc objects should be destroyed when they are no longer needed.
206:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
207:   MatDestroy(&A);
208:   VecDestroy(&U);
209:   TSDestroy(&ts);

211:   PetscFinalize();
212:   return(0);
213: }