Actual source code: ssp.c

      1: /*
      2:        Code for Timestepping with explicit SSP.
      3: */
      4: #include <petsc/private/tsimpl.h>

      6: PetscFunctionList TSSSPList = NULL;
      7: static PetscBool  TSSSPPackageInitialized;

      9: typedef struct {
     10:   PetscErrorCode (*onestep)(TS, PetscReal, PetscReal, Vec);
     11:   char     *type_name;
     12:   PetscInt  nstages;
     13:   Vec      *work;
     14:   PetscInt  nwork;
     15:   PetscBool workout;
     16: } TS_SSP;

     18: static PetscErrorCode TSSSPGetWorkVectors(TS ts, PetscInt n, Vec **work)
     19: {
     20:   TS_SSP *ssp = (TS_SSP *)ts->data;

     22:   PetscFunctionBegin;
     23:   PetscCheck(!ssp->workout, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Work vectors already gotten");
     24:   if (ssp->nwork < n) {
     25:     if (ssp->nwork > 0) PetscCall(VecDestroyVecs(ssp->nwork, &ssp->work));
     26:     PetscCall(VecDuplicateVecs(ts->vec_sol, n, &ssp->work));
     27:     ssp->nwork = n;
     28:   }
     29:   *work        = ssp->work;
     30:   ssp->workout = PETSC_TRUE;
     31:   PetscFunctionReturn(PETSC_SUCCESS);
     32: }

     34: static PetscErrorCode TSSSPRestoreWorkVectors(TS ts, PetscInt n, Vec **work)
     35: {
     36:   TS_SSP *ssp = (TS_SSP *)ts->data;

     38:   PetscFunctionBegin;
     39:   PetscCheck(ssp->workout, PETSC_COMM_SELF, PETSC_ERR_ORDER, "Work vectors have not been gotten");
     40:   PetscCheck(*work == ssp->work, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Wrong work vectors checked out");
     41:   ssp->workout = PETSC_FALSE;
     42:   *work        = NULL;
     43:   PetscFunctionReturn(PETSC_SUCCESS);
     44: }

     46: /*MC
     47:    TSSSPRKS2 - Optimal second order SSP Runge-Kutta method, low-storage, c_eff=(s-1)/s. Pseudocode 2 of {cite}`ketcheson_2008`

     49:    Level: beginner

     51: .seealso: [](ch_ts), `TSSSP`, `TSSSPSetType()`, `TSSSPSetNumStages()`
     52: M*/
     53: static PetscErrorCode TSSSPStep_RK_2(TS ts, PetscReal t0, PetscReal dt, Vec sol)
     54: {
     55:   TS_SSP  *ssp = (TS_SSP *)ts->data;
     56:   Vec     *work, F;
     57:   PetscInt i, s;

     59:   PetscFunctionBegin;
     60:   s = ssp->nstages;
     61:   PetscCall(TSSSPGetWorkVectors(ts, 2, &work));
     62:   F = work[1];
     63:   PetscCall(VecCopy(sol, work[0]));
     64:   for (i = 0; i < s - 1; i++) {
     65:     PetscReal stage_time = t0 + dt * (i / (s - 1.));
     66:     PetscCall(TSPreStage(ts, stage_time));
     67:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
     68:     PetscCall(VecAXPY(work[0], dt / (s - 1.), F));
     69:   }
     70:   PetscCall(TSComputeRHSFunction(ts, t0 + dt, work[0], F));
     71:   PetscCall(VecAXPBYPCZ(sol, (s - 1.) / s, dt / s, 1. / s, work[0], F));
     72:   PetscCall(TSSSPRestoreWorkVectors(ts, 2, &work));
     73:   PetscFunctionReturn(PETSC_SUCCESS);
     74: }

     76: /*MC
     77:    TSSSPRKS3 - Optimal third order SSP Runge-Kutta, low-storage, $c_eff=(PetscSqrtReal(s)-1)/PetscSqrtReal(s)$, where `PetscSqrtReal`(s) is an integer

     79:    Pseudocode 2 of {cite}`ketcheson_2008`

     81:    Level: beginner

     83: .seealso: [](ch_ts), `TSSSP`, `TSSSPSetType()`, `TSSSPSetNumStages()`
     84: M*/
     85: static PetscErrorCode TSSSPStep_RK_3(TS ts, PetscReal t0, PetscReal dt, Vec sol)
     86: {
     87:   TS_SSP   *ssp = (TS_SSP *)ts->data;
     88:   Vec      *work, F;
     89:   PetscInt  i, s, n, r;
     90:   PetscReal c, stage_time;

     92:   PetscFunctionBegin;
     93:   s = ssp->nstages;
     94:   n = (PetscInt)(PetscSqrtReal((PetscReal)s) + 0.001);
     95:   r = s - n;
     96:   PetscCheck(n * n == s, PETSC_COMM_SELF, PETSC_ERR_SUP, "No support for optimal third order schemes with %" PetscInt_FMT " stages, must be a square number at least 4", s);
     97:   PetscCall(TSSSPGetWorkVectors(ts, 3, &work));
     98:   F = work[2];
     99:   PetscCall(VecCopy(sol, work[0]));
    100:   for (i = 0; i < (n - 1) * (n - 2) / 2; i++) {
    101:     c          = (i < n * (n + 1) / 2) ? 1. * i / (s - n) : (1. * i - n) / (s - n);
    102:     stage_time = t0 + c * dt;
    103:     PetscCall(TSPreStage(ts, stage_time));
    104:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    105:     PetscCall(VecAXPY(work[0], dt / r, F));
    106:   }
    107:   PetscCall(VecCopy(work[0], work[1]));
    108:   for (; i < n * (n + 1) / 2 - 1; i++) {
    109:     c          = (i < n * (n + 1) / 2) ? 1. * i / (s - n) : (1. * i - n) / (s - n);
    110:     stage_time = t0 + c * dt;
    111:     PetscCall(TSPreStage(ts, stage_time));
    112:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    113:     PetscCall(VecAXPY(work[0], dt / r, F));
    114:   }
    115:   {
    116:     c          = (i < n * (n + 1) / 2) ? 1. * i / (s - n) : (1. * i - n) / (s - n);
    117:     stage_time = t0 + c * dt;
    118:     PetscCall(TSPreStage(ts, stage_time));
    119:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    120:     PetscCall(VecAXPBYPCZ(work[0], 1. * n / (2 * n - 1.), (n - 1.) * dt / (r * (2 * n - 1)), (n - 1.) / (2 * n - 1.), work[1], F));
    121:     i++;
    122:   }
    123:   for (; i < s; i++) {
    124:     c          = (i < n * (n + 1) / 2) ? 1. * i / (s - n) : (1. * i - n) / (s - n);
    125:     stage_time = t0 + c * dt;
    126:     PetscCall(TSPreStage(ts, stage_time));
    127:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    128:     PetscCall(VecAXPY(work[0], dt / r, F));
    129:   }
    130:   PetscCall(VecCopy(work[0], sol));
    131:   PetscCall(TSSSPRestoreWorkVectors(ts, 3, &work));
    132:   PetscFunctionReturn(PETSC_SUCCESS);
    133: }

    135: /*MC
    136:    TSSSPRKS104 - Optimal fourth order SSP Runge-Kutta, low-storage (2N), c_eff=0.6

    138:    SSPRK(10,4), Pseudocode 3 of {cite}`ketcheson_2008`

    140:    Level: beginner

    142: .seealso: [](ch_ts), `TSSSP`, `TSSSPSetType()`
    143: M*/
    144: static PetscErrorCode TSSSPStep_RK_10_4(TS ts, PetscReal t0, PetscReal dt, Vec sol)
    145: {
    146:   const PetscReal c[10] = {0, 1. / 6, 2. / 6, 3. / 6, 4. / 6, 2. / 6, 3. / 6, 4. / 6, 5. / 6, 1};
    147:   Vec            *work, F;
    148:   PetscInt        i;
    149:   PetscReal       stage_time;

    151:   PetscFunctionBegin;
    152:   PetscCall(TSSSPGetWorkVectors(ts, 3, &work));
    153:   F = work[2];
    154:   PetscCall(VecCopy(sol, work[0]));
    155:   for (i = 0; i < 5; i++) {
    156:     stage_time = t0 + c[i] * dt;
    157:     PetscCall(TSPreStage(ts, stage_time));
    158:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    159:     PetscCall(VecAXPY(work[0], dt / 6, F));
    160:   }
    161:   PetscCall(VecAXPBYPCZ(work[1], 1. / 25, 9. / 25, 0, sol, work[0]));
    162:   PetscCall(VecAXPBY(work[0], 15, -5, work[1]));
    163:   for (; i < 9; i++) {
    164:     stage_time = t0 + c[i] * dt;
    165:     PetscCall(TSPreStage(ts, stage_time));
    166:     PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    167:     PetscCall(VecAXPY(work[0], dt / 6, F));
    168:   }
    169:   stage_time = t0 + dt;
    170:   PetscCall(TSPreStage(ts, stage_time));
    171:   PetscCall(TSComputeRHSFunction(ts, stage_time, work[0], F));
    172:   PetscCall(VecAXPBYPCZ(work[1], 3. / 5, dt / 10, 1, work[0], F));
    173:   PetscCall(VecCopy(work[1], sol));
    174:   PetscCall(TSSSPRestoreWorkVectors(ts, 3, &work));
    175:   PetscFunctionReturn(PETSC_SUCCESS);
    176: }

    178: static PetscErrorCode TSSetUp_SSP(TS ts)
    179: {
    180:   PetscFunctionBegin;
    181:   PetscCall(TSCheckImplicitTerm(ts));
    182:   PetscCall(TSGetAdapt(ts, &ts->adapt));
    183:   PetscCall(TSAdaptCandidatesClear(ts->adapt));
    184:   PetscFunctionReturn(PETSC_SUCCESS);
    185: }

    187: static PetscErrorCode TSStep_SSP(TS ts)
    188: {
    189:   TS_SSP   *ssp = (TS_SSP *)ts->data;
    190:   Vec       sol = ts->vec_sol;
    191:   PetscBool stageok, accept = PETSC_TRUE;
    192:   PetscReal next_time_step = ts->time_step;

    194:   PetscFunctionBegin;
    195:   PetscCall((*ssp->onestep)(ts, ts->ptime, ts->time_step, sol));
    196:   PetscCall(TSPostStage(ts, ts->ptime, 0, &sol));
    197:   PetscCall(TSAdaptCheckStage(ts->adapt, ts, ts->ptime + ts->time_step, sol, &stageok));
    198:   if (!stageok) {
    199:     ts->reason = TS_DIVERGED_STEP_REJECTED;
    200:     PetscFunctionReturn(PETSC_SUCCESS);
    201:   }

    203:   PetscCall(TSAdaptChoose(ts->adapt, ts, ts->time_step, NULL, &next_time_step, &accept));
    204:   if (!accept) {
    205:     ts->reason = TS_DIVERGED_STEP_REJECTED;
    206:     PetscFunctionReturn(PETSC_SUCCESS);
    207:   }

    209:   ts->ptime += ts->time_step;
    210:   ts->time_step = next_time_step;
    211:   PetscFunctionReturn(PETSC_SUCCESS);
    212: }

    214: static PetscErrorCode TSReset_SSP(TS ts)
    215: {
    216:   TS_SSP *ssp = (TS_SSP *)ts->data;

    218:   PetscFunctionBegin;
    219:   if (ssp->work) PetscCall(VecDestroyVecs(ssp->nwork, &ssp->work));
    220:   ssp->nwork   = 0;
    221:   ssp->workout = PETSC_FALSE;
    222:   PetscFunctionReturn(PETSC_SUCCESS);
    223: }

    225: static PetscErrorCode TSDestroy_SSP(TS ts)
    226: {
    227:   TS_SSP *ssp = (TS_SSP *)ts->data;

    229:   PetscFunctionBegin;
    230:   PetscCall(TSReset_SSP(ts));
    231:   PetscCall(PetscFree(ssp->type_name));
    232:   PetscCall(PetscFree(ts->data));
    233:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPGetType_C", NULL));
    234:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPSetType_C", NULL));
    235:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPGetNumStages_C", NULL));
    236:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPSetNumStages_C", NULL));
    237:   PetscFunctionReturn(PETSC_SUCCESS);
    238: }

    240: /*@
    241:   TSSSPSetType - set the `TSSSP` time integration scheme to use

    243:   Logically Collective

    245:   Input Parameters:
    246: + ts      - time stepping object
    247: - ssptype - type of scheme to use

    249:   Options Database Keys:
    250: + -ts_ssp_type (rks2|rks3|rk104) - Type of `TSSSP` method, see `TSSSPType`
    251: - -ts_ssp_num_stages nstages     - Number of stages

    253:   Level: beginner

    255: .seealso: [](ch_ts), `TSSSP`, `TSSSPGetType()`, `TSSSPSetNumStages()`, `TSSSPRKS2`, `TSSSPRKS3`, `TSSSPRK104`
    256: @*/
    257: PetscErrorCode TSSSPSetType(TS ts, TSSSPType ssptype)
    258: {
    259:   PetscFunctionBegin;
    261:   PetscAssertPointer(ssptype, 2);
    262:   PetscTryMethod(ts, "TSSSPSetType_C", (TS, TSSSPType), (ts, ssptype));
    263:   PetscFunctionReturn(PETSC_SUCCESS);
    264: }

    266: /*@
    267:   TSSSPGetType - get the `TSSSP` time integration scheme

    269:   Logically Collective

    271:   Input Parameter:
    272: . ts - time stepping object

    274:   Output Parameter:
    275: . type - type of scheme being used

    277:   Level: beginner

    279: .seealso: [](ch_ts), `TSSSP`, `TSSSPSetType()`, `TSSSPSetNumStages()`, `TSSSPRKS2`, `TSSSPRKS3`, `TSSSPRK104`
    280: @*/
    281: PetscErrorCode TSSSPGetType(TS ts, TSSSPType *type)
    282: {
    283:   PetscFunctionBegin;
    285:   PetscUseMethod(ts, "TSSSPGetType_C", (TS, TSSSPType *), (ts, type));
    286:   PetscFunctionReturn(PETSC_SUCCESS);
    287: }

    289: /*@
    290:   TSSSPSetNumStages - set the number of stages to use with the `TSSSP` method. Must be called after
    291:   `TSSSPSetType()`.

    293:   Logically Collective

    295:   Input Parameters:
    296: + ts      - time stepping object
    297: - nstages - number of stages

    299:   Options Database Keys:
    300: + -ts_ssp_type (rks2|rks3|rk104) - Type of `TSSSP` method, see `TSSSPType`
    301: - -ts_ssp_num_stages nstages     - number of stages

    303:   Level: beginner

    305: .seealso: [](ch_ts), `TSSSP`, `TSSSPGetNumStages()`, `TSSSPRKS2`, `TSSSPRKS3`, `TSSSPRK104`
    306: @*/
    307: PetscErrorCode TSSSPSetNumStages(TS ts, PetscInt nstages)
    308: {
    309:   PetscFunctionBegin;
    311:   PetscTryMethod(ts, "TSSSPSetNumStages_C", (TS, PetscInt), (ts, nstages));
    312:   PetscFunctionReturn(PETSC_SUCCESS);
    313: }

    315: /*@
    316:   TSSSPGetNumStages - get the number of stages in the `TSSSP` time integration scheme

    318:   Logically Collective

    320:   Input Parameter:
    321: . ts - time stepping object

    323:   Output Parameter:
    324: . nstages - number of stages

    326:   Level: beginner

    328: .seealso: [](ch_ts), `TSSSP`, `TSSSPGetType()`, `TSSSPSetNumStages()`, `TSSSPRKS2`, `TSSSPRKS3`, `TSSSPRK104`
    329: @*/
    330: PetscErrorCode TSSSPGetNumStages(TS ts, PetscInt *nstages)
    331: {
    332:   PetscFunctionBegin;
    334:   PetscUseMethod(ts, "TSSSPGetNumStages_C", (TS, PetscInt *), (ts, nstages));
    335:   PetscFunctionReturn(PETSC_SUCCESS);
    336: }

    338: static PetscErrorCode TSSSPSetType_SSP(TS ts, TSSSPType type)
    339: {
    340:   TS_SSP *ssp = (TS_SSP *)ts->data;
    341:   PetscErrorCode (*r)(TS, PetscReal, PetscReal, Vec);
    342:   PetscBool flag;

    344:   PetscFunctionBegin;
    345:   PetscCall(PetscFunctionListFind(TSSSPList, type, &r));
    346:   PetscCheck(r, PetscObjectComm((PetscObject)ts), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unknown TS_SSP type %s given", type);
    347:   ssp->onestep = r;
    348:   PetscCall(PetscFree(ssp->type_name));
    349:   PetscCall(PetscStrallocpy(type, &ssp->type_name));
    350:   ts->default_adapt_type = TSADAPTNONE;
    351:   PetscCall(PetscStrcmp(type, TSSSPRKS2, &flag));
    352:   if (flag) {
    353:     ssp->nstages = 5;
    354:   } else {
    355:     PetscCall(PetscStrcmp(type, TSSSPRKS3, &flag));
    356:     if (flag) {
    357:       ssp->nstages = 9;
    358:     } else {
    359:       ssp->nstages = 5;
    360:     }
    361:   }
    362:   PetscFunctionReturn(PETSC_SUCCESS);
    363: }
    364: static PetscErrorCode TSSSPGetType_SSP(TS ts, TSSSPType *type)
    365: {
    366:   TS_SSP *ssp = (TS_SSP *)ts->data;

    368:   PetscFunctionBegin;
    369:   *type = ssp->type_name;
    370:   PetscFunctionReturn(PETSC_SUCCESS);
    371: }
    372: static PetscErrorCode TSSSPSetNumStages_SSP(TS ts, PetscInt nstages)
    373: {
    374:   TS_SSP *ssp = (TS_SSP *)ts->data;

    376:   PetscFunctionBegin;
    377:   ssp->nstages = nstages;
    378:   PetscFunctionReturn(PETSC_SUCCESS);
    379: }
    380: static PetscErrorCode TSSSPGetNumStages_SSP(TS ts, PetscInt *nstages)
    381: {
    382:   TS_SSP *ssp = (TS_SSP *)ts->data;

    384:   PetscFunctionBegin;
    385:   *nstages = ssp->nstages;
    386:   PetscFunctionReturn(PETSC_SUCCESS);
    387: }

    389: static PetscErrorCode TSSetFromOptions_SSP(TS ts, PetscOptionItems PetscOptionsObject)
    390: {
    391:   char      tname[256] = TSSSPRKS2;
    392:   TS_SSP   *ssp        = (TS_SSP *)ts->data;
    393:   PetscBool flg;

    395:   PetscFunctionBegin;
    396:   PetscOptionsHeadBegin(PetscOptionsObject, "SSP ODE solver options");
    397:   {
    398:     PetscCall(PetscOptionsFList("-ts_ssp_type", "Type of SSP method", "TSSSPSetType", TSSSPList, tname, tname, sizeof(tname), &flg));
    399:     if (flg) PetscCall(TSSSPSetType(ts, tname));
    400:     PetscCall(PetscOptionsInt("-ts_ssp_num_stages", "Number of stages", "TSSSPSetNumStages", ssp->nstages, &ssp->nstages, NULL));
    401:   }
    402:   PetscOptionsHeadEnd();
    403:   PetscFunctionReturn(PETSC_SUCCESS);
    404: }

    406: static PetscErrorCode TSView_SSP(TS ts, PetscViewer viewer)
    407: {
    408:   TS_SSP   *ssp = (TS_SSP *)ts->data;
    409:   PetscBool ascii;

    411:   PetscFunctionBegin;
    412:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &ascii));
    413:   if (ascii) PetscCall(PetscViewerASCIIPrintf(viewer, "  Scheme: %s\n", ssp->type_name));
    414:   PetscFunctionReturn(PETSC_SUCCESS);
    415: }

    417: /*MC
    418:       TSSSP - Explicit strong stability preserving ODE solver {cite}`ketcheson_2008` {cite}`gottliebketchesonshu2009`

    420:   Most hyperbolic conservation laws have exact solutions that are total variation diminishing (TVD) or total variation
    421:   bounded (TVB) although these solutions often contain discontinuities.  Spatial discretizations such as Godunov's
    422:   scheme and high-resolution finite volume methods (TVD limiters, ENO/WENO) are designed to preserve these properties,
    423:   but they are usually formulated using a forward Euler time discretization or by coupling the space and time
    424:   discretization as in the classical Lax-Wendroff scheme.  When the space and time discretization is coupled, it is very
    425:   difficult to produce schemes with high temporal accuracy while preserving TVD properties.  An alternative is the
    426:   semidiscrete formulation where we choose a spatial discretization that is TVD with forward Euler and then choose a
    427:   time discretization that preserves the TVD property.  Such integrators are called strong stability preserving (SSP).

    429:   Let c_eff be the minimum number of function evaluations required to step as far as one step of forward Euler while
    430:   still being SSP.  Some theoretical bounds

    432:   1. There are no explicit methods with c_eff > 1.

    434:   2. There are no explicit methods beyond order 4 (for nonlinear problems) and c_eff > 0.

    436:   3. There are no implicit methods with order greater than 1 and c_eff > 2.

    438:   This integrator provides Runge-Kutta methods of order 2, 3, and 4 with maximal values of c_eff.  More stages allows
    439:   for larger values of c_eff which improves efficiency.  These implementations are low-memory and only use 2 or 3 work
    440:   vectors regardless of the total number of stages, so e.g. 25-stage 3rd order methods may be an excellent choice.

    442:   Methods can be chosen with -ts_ssp_type {rks2,rks3,rk104}

    444:   rks2: Second order methods with any number s>1 of stages.  c_eff = (s-1)/s

    446:   rks3: Third order methods with s=n^2 stages, n>1.  c_eff = (s-n)/s

    448:   rk104: A 10-stage fourth order method.  c_eff = 0.6

    450:   Level: beginner

    452: .seealso: [](ch_ts), `TSCreate()`, `TS`, `TSSetType()`
    453: M*/
    454: PETSC_EXTERN PetscErrorCode TSCreate_SSP(TS ts)
    455: {
    456:   TS_SSP *ssp;

    458:   PetscFunctionBegin;
    459:   PetscCall(TSSSPInitializePackage());

    461:   ts->ops->setup          = TSSetUp_SSP;
    462:   ts->ops->step           = TSStep_SSP;
    463:   ts->ops->reset          = TSReset_SSP;
    464:   ts->ops->destroy        = TSDestroy_SSP;
    465:   ts->ops->setfromoptions = TSSetFromOptions_SSP;
    466:   ts->ops->view           = TSView_SSP;

    468:   PetscCall(PetscNew(&ssp));
    469:   ts->data = (void *)ssp;

    471:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPGetType_C", TSSSPGetType_SSP));
    472:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPSetType_C", TSSSPSetType_SSP));
    473:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPGetNumStages_C", TSSSPGetNumStages_SSP));
    474:   PetscCall(PetscObjectComposeFunction((PetscObject)ts, "TSSSPSetNumStages_C", TSSSPSetNumStages_SSP));

    476:   PetscCall(TSSSPSetType(ts, TSSSPRKS2));
    477:   PetscFunctionReturn(PETSC_SUCCESS);
    478: }

    480: /*@C
    481:   TSSSPInitializePackage - This function initializes everything in the `TSSSP` package. It is called
    482:   from `TSInitializePackage()`.

    484:   Level: developer

    486: .seealso: [](ch_ts), `PetscInitialize()`, `TSSSPFinalizePackage()`, `TSInitializePackage()`
    487: @*/
    488: PetscErrorCode TSSSPInitializePackage(void)
    489: {
    490:   PetscFunctionBegin;
    491:   if (TSSSPPackageInitialized) PetscFunctionReturn(PETSC_SUCCESS);
    492:   TSSSPPackageInitialized = PETSC_TRUE;
    493:   PetscCall(PetscFunctionListAdd(&TSSSPList, TSSSPRKS2, TSSSPStep_RK_2));
    494:   PetscCall(PetscFunctionListAdd(&TSSSPList, TSSSPRKS3, TSSSPStep_RK_3));
    495:   PetscCall(PetscFunctionListAdd(&TSSSPList, TSSSPRK104, TSSSPStep_RK_10_4));
    496:   PetscCall(PetscRegisterFinalize(TSSSPFinalizePackage));
    497:   PetscFunctionReturn(PETSC_SUCCESS);
    498: }

    500: /*@C
    501:   TSSSPFinalizePackage - This function destroys everything in the `TSSSP` package. It is
    502:   called from `PetscFinalize()`.

    504:   Level: developer

    506: .seealso: [](ch_ts), `PetscFinalize()`, `TSSSPInitiallizePackage()`, `TSInitializePackage()`
    507: @*/
    508: PetscErrorCode TSSSPFinalizePackage(void)
    509: {
    510:   PetscFunctionBegin;
    511:   TSSSPPackageInitialized = PETSC_FALSE;
    512:   PetscCall(PetscFunctionListDestroy(&TSSSPList));
    513:   PetscFunctionReturn(PETSC_SUCCESS);
    514: }