Actual source code: ex3.c
petsc-3.13.6 2020-09-29
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      1: static char help[] = "Newton methods to solve u'' + u^{2} = f in parallel.\n\
      2: This example employs a user-defined monitoring routine and optionally a user-defined\n\
      3: routine to check candidate iterates produced by line search routines.\n\
      4: The command line options include:\n\
      5:   -pre_check_iterates : activate checking of iterates\n\
      6:   -post_check_iterates : activate checking of iterates\n\
      7:   -check_tol <tol>: set tolerance for iterate checking\n\
      8:   -user_precond : activate a (trivial) user-defined preconditioner\n\n";

     10: /*T
     11:    Concepts: SNES^basic parallel example
     12:    Concepts: SNES^setting a user-defined monitoring routine
     13:    Processors: n
     14: T*/

     18: /*
     19:    Include "petscdm.h" so that we can use data management objects (DMs)
     20:    Include "petscdmda.h" so that we can use distributed arrays (DMDAs).
     21:    Include "petscsnes.h" so that we can use SNES solvers.  Note that this
     22:    file automatically includes:
     23:      petscsys.h    - base PETSc routines
     24:      petscvec.h    - vectors
     25:      petscmat.h    - matrices
     26:      petscis.h     - index sets
     27:      petscksp.h    - Krylov subspace methods
     28:      petscviewer.h - viewers
     29:      petscpc.h     - preconditioners
     30:      petscksp.h    - linear solvers
     31: */

     33:  #include <petscdm.h>
     34:  #include <petscdmda.h>
     35:  #include <petscsnes.h>

     37: /*
     38:    User-defined routines.
     39: */
     40: PetscErrorCode FormJacobian(SNES,Vec,Mat,Mat,void*);
     41: PetscErrorCode FormFunction(SNES,Vec,Vec,void*);
     42: PetscErrorCode FormInitialGuess(Vec);
     43: PetscErrorCode Monitor(SNES,PetscInt,PetscReal,void*);
     44: PetscErrorCode PreCheck(SNESLineSearch,Vec,Vec,PetscBool*,void*);
     45: PetscErrorCode PostCheck(SNESLineSearch,Vec,Vec,Vec,PetscBool*,PetscBool*,void*);
     46: PetscErrorCode PostSetSubKSP(SNESLineSearch,Vec,Vec,Vec,PetscBool*,PetscBool*,void*);
     47: PetscErrorCode MatrixFreePreconditioner(PC,Vec,Vec);

     49: /*
     50:    User-defined Section 1.5 Writing Application Codes with PETSc context
     51: */
     52: typedef struct {
     53:   DM          da;      /* distributed array */
     54:   Vec         F;       /* right-hand-side of PDE */
     55:   PetscMPIInt rank;    /* rank of processor */
     56:   PetscMPIInt size;    /* size of communicator */
     57:   PetscReal   h;       /* mesh spacing */
     58:   PetscBool   sjerr;   /* if or not to test jacobian domain error */
     59: } ApplicationCtx;

     61: /*
     62:    User-defined context for monitoring
     63: */
     64: typedef struct {
     65:   PetscViewer viewer;
     66: } MonitorCtx;

     68: /*
     69:    User-defined context for checking candidate iterates that are
     70:    determined by line search methods
     71: */
     72: typedef struct {
     73:   Vec            last_step;  /* previous iterate */
     74:   PetscReal      tolerance;  /* tolerance for changes between successive iterates */
     75:   ApplicationCtx *user;
     76: } StepCheckCtx;

     78: typedef struct {
     79:   PetscInt its0; /* num of prevous outer KSP iterations */
     80: } SetSubKSPCtx;

     82: int main(int argc,char **argv)
     83: {
     84:   SNES           snes;                 /* SNES context */
     85:   SNESLineSearch linesearch;           /* SNESLineSearch context */
     86:   Mat            J;                    /* Jacobian matrix */
     87:   ApplicationCtx ctx;                  /* user-defined context */
     88:   Vec            x,r,U,F;              /* vectors */
     89:   MonitorCtx     monP;                 /* monitoring context */
     90:   StepCheckCtx   checkP;               /* step-checking context */
     91:   SetSubKSPCtx   checkP1;
     92:   PetscBool      pre_check,post_check,post_setsubksp; /* flag indicating whether we're checking candidate iterates */
     93:   PetscScalar    xp,*FF,*UU,none = -1.0;
     95:   PetscInt       its,N = 5,i,maxit,maxf,xs,xm;
     96:   PetscReal      abstol,rtol,stol,norm;
     97:   PetscBool      flg;

    100:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
    101:   MPI_Comm_rank(PETSC_COMM_WORLD,&ctx.rank);
    102:   MPI_Comm_size(PETSC_COMM_WORLD,&ctx.size);
    103:   PetscOptionsGetInt(NULL,NULL,"-n",&N,NULL);
    104:   ctx.h = 1.0/(N-1);
    105:   ctx.sjerr = PETSC_FALSE;
    106:   PetscOptionsGetBool(NULL,NULL,"-test_jacobian_domain_error",&ctx.sjerr,NULL);

    108:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    109:      Create nonlinear solver context
    110:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    112:   SNESCreate(PETSC_COMM_WORLD,&snes);

    114:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    115:      Create vector data structures; set function evaluation routine
    116:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    118:   /*
    119:      Create distributed array (DMDA) to manage parallel grid and vectors
    120:   */
    121:   DMDACreate1d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,N,1,1,NULL,&ctx.da);
    122:   DMSetFromOptions(ctx.da);
    123:   DMSetUp(ctx.da);

    125:   /*
    126:      Extract global and local vectors from DMDA; then duplicate for remaining
    127:      vectors that are the same types
    128:   */
    129:   DMCreateGlobalVector(ctx.da,&x);
    130:   VecDuplicate(x,&r);
    131:   VecDuplicate(x,&F); ctx.F = F;
    132:   VecDuplicate(x,&U);

    134:   /*
    135:      Set function evaluation routine and vector.  Whenever the nonlinear
    136:      solver needs to compute the nonlinear function, it will call this
    137:      routine.
    138:       - Note that the final routine argument is the user-defined
    139:         context that provides Section 1.5 Writing Application Codes with PETSc-specific data for the
    140:         function evaluation routine.
    141:   */
    142:   SNESSetFunction(snes,r,FormFunction,&ctx);

    144:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    145:      Create matrix data structure; set Jacobian evaluation routine
    146:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    148:   MatCreate(PETSC_COMM_WORLD,&J);
    149:   MatSetSizes(J,PETSC_DECIDE,PETSC_DECIDE,N,N);
    150:   MatSetFromOptions(J);
    151:   MatSeqAIJSetPreallocation(J,3,NULL);
    152:   MatMPIAIJSetPreallocation(J,3,NULL,3,NULL);

    154:   /*
    155:      Set Jacobian matrix data structure and default Jacobian evaluation
    156:      routine.  Whenever the nonlinear solver needs to compute the
    157:      Jacobian matrix, it will call this routine.
    158:       - Note that the final routine argument is the user-defined
    159:         context that provides Section 1.5 Writing Application Codes with PETSc-specific data for the
    160:         Jacobian evaluation routine.
    161:   */
    162:   SNESSetJacobian(snes,J,J,FormJacobian,&ctx);

    164:   /*
    165:      Optionally allow user-provided preconditioner
    166:    */
    167:   PetscOptionsHasName(NULL,NULL,"-user_precond",&flg);
    168:   if (flg) {
    169:     KSP ksp;
    170:     PC  pc;
    171:     SNESGetKSP(snes,&ksp);
    172:     KSPGetPC(ksp,&pc);
    173:     PCSetType(pc,PCSHELL);
    174:     PCShellSetApply(pc,MatrixFreePreconditioner);
    175:   }

    177:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    178:      Customize nonlinear solver; set runtime options
    179:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    181:   /*
    182:      Set an optional user-defined monitoring routine
    183:   */
    184:   PetscViewerDrawOpen(PETSC_COMM_WORLD,0,0,0,0,400,400,&monP.viewer);
    185:   SNESMonitorSet(snes,Monitor,&monP,0);

    187:   /*
    188:      Set names for some vectors to facilitate monitoring (optional)
    189:   */
    190:   PetscObjectSetName((PetscObject)x,"Approximate Solution");
    191:   PetscObjectSetName((PetscObject)U,"Exact Solution");

    193:   /*
    194:      Set SNES/KSP/KSP/PC runtime options, e.g.,
    195:          -snes_view -snes_monitor -ksp_type <ksp> -pc_type <pc>
    196:   */
    197:   SNESSetFromOptions(snes);

    199:   /*
    200:      Set an optional user-defined routine to check the validity of candidate
    201:      iterates that are determined by line search methods
    202:   */
    203:   SNESGetLineSearch(snes, &linesearch);
    204:   PetscOptionsHasName(NULL,NULL,"-post_check_iterates",&post_check);

    206:   if (post_check) {
    207:     PetscPrintf(PETSC_COMM_WORLD,"Activating post step checking routine\n");
    208:     SNESLineSearchSetPostCheck(linesearch,PostCheck,&checkP);
    209:     VecDuplicate(x,&(checkP.last_step));

    211:     checkP.tolerance = 1.0;
    212:     checkP.user      = &ctx;

    214:     PetscOptionsGetReal(NULL,NULL,"-check_tol",&checkP.tolerance,NULL);
    215:   }

    217:   PetscOptionsHasName(NULL,NULL,"-post_setsubksp",&post_setsubksp);
    218:   if (post_setsubksp) {
    219:     PetscPrintf(PETSC_COMM_WORLD,"Activating post setsubksp\n");
    220:     SNESLineSearchSetPostCheck(linesearch,PostSetSubKSP,&checkP1);
    221:   }

    223:   PetscOptionsHasName(NULL,NULL,"-pre_check_iterates",&pre_check);
    224:   if (pre_check) {
    225:     PetscPrintf(PETSC_COMM_WORLD,"Activating pre step checking routine\n");
    226:     SNESLineSearchSetPreCheck(linesearch,PreCheck,&checkP);
    227:   }

    229:   /*
    230:      Print parameters used for convergence testing (optional) ... just
    231:      to demonstrate this routine; this information is also printed with
    232:      the option -snes_view
    233:   */
    234:   SNESGetTolerances(snes,&abstol,&rtol,&stol,&maxit,&maxf);
    235:   PetscPrintf(PETSC_COMM_WORLD,"atol=%g, rtol=%g, stol=%g, maxit=%D, maxf=%D\n",(double)abstol,(double)rtol,(double)stol,maxit,maxf);

    237:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    238:      Initialize Section 1.5 Writing Application Codes with PETSc:
    239:      Store right-hand-side of PDE and exact solution
    240:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    242:   /*
    243:      Get local grid boundaries (for 1-dimensional DMDA):
    244:        xs, xm - starting grid index, width of local grid (no ghost points)
    245:   */
    246:   DMDAGetCorners(ctx.da,&xs,NULL,NULL,&xm,NULL,NULL);

    248:   /*
    249:      Get pointers to vector data
    250:   */
    251:   DMDAVecGetArray(ctx.da,F,&FF);
    252:   DMDAVecGetArray(ctx.da,U,&UU);

    254:   /*
    255:      Compute local vector entries
    256:   */
    257:   xp = ctx.h*xs;
    258:   for (i=xs; i<xs+xm; i++) {
    259:     FF[i] = 6.0*xp + PetscPowScalar(xp+1.e-12,6.0); /* +1.e-12 is to prevent 0^6 */
    260:     UU[i] = xp*xp*xp;
    261:     xp   += ctx.h;
    262:   }

    264:   /*
    265:      Restore vectors
    266:   */
    267:   DMDAVecRestoreArray(ctx.da,F,&FF);
    268:   DMDAVecRestoreArray(ctx.da,U,&UU);

    270:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    271:      Evaluate initial guess; then solve nonlinear system
    272:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    274:   /*
    275:      Note: The user should initialize the vector, x, with the initial guess
    276:      for the nonlinear solver prior to calling SNESSolve().  In particular,
    277:      to employ an initial guess of zero, the user should explicitly set
    278:      this vector to zero by calling VecSet().
    279:   */
    280:   FormInitialGuess(x);
    281:   SNESSolve(snes,NULL,x);
    282:   SNESGetIterationNumber(snes,&its);
    283:   PetscPrintf(PETSC_COMM_WORLD,"Number of SNES iterations = %D\n",its);

    285:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    286:      Check solution and clean up
    287:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    289:   /*
    290:      Check the error
    291:   */
    292:   VecAXPY(x,none,U);
    293:   VecNorm(x,NORM_2,&norm);
    294:   PetscPrintf(PETSC_COMM_WORLD,"Norm of error %g Iterations %D\n",(double)norm,its);
    295:   if (ctx.sjerr) {
    296:     SNESType       snestype;
    297:     SNESGetType(snes,&snestype);
    298:     PetscPrintf(PETSC_COMM_WORLD,"SNES Type %s\n",snestype);
    299:   }

    301:   /*
    302:      Free work space.  All PETSc objects should be destroyed when they
    303:      are no longer needed.
    304:   */
    305:   PetscViewerDestroy(&monP.viewer);
    306:   if (post_check) {VecDestroy(&checkP.last_step);}
    307:   VecDestroy(&x);
    308:   VecDestroy(&r);
    309:   VecDestroy(&U);
    310:   VecDestroy(&F);
    311:   MatDestroy(&J);
    312:   SNESDestroy(&snes);
    313:   DMDestroy(&ctx.da);
    314:   PetscFinalize();
    315:   return ierr;
    316: }

    318: /* ------------------------------------------------------------------- */
    319: /*
    320:    FormInitialGuess - Computes initial guess.

    322:    Input/Output Parameter:
    323: .  x - the solution vector
    324: */
    325: PetscErrorCode FormInitialGuess(Vec x)
    326: {
    328:   PetscScalar    pfive = .50;

    331:   VecSet(x,pfive);
    332:   return(0);
    333: }

    335: /* ------------------------------------------------------------------- */
    336: /*
    337:    FormFunction - Evaluates nonlinear function, F(x).

    339:    Input Parameters:
    340: .  snes - the SNES context
    341: .  x - input vector
    342: .  ctx - optional user-defined context, as set by SNESSetFunction()

    344:    Output Parameter:
    345: .  f - function vector

    347:    Note:
    348:    The user-defined context can contain any Section 1.5 Writing Application Codes with PETSc-specific
    349:    data needed for the function evaluation.
    350: */
    351: PetscErrorCode FormFunction(SNES snes,Vec x,Vec f,void *ctx)
    352: {
    353:   ApplicationCtx *user = (ApplicationCtx*) ctx;
    354:   DM             da    = user->da;
    355:   PetscScalar    *xx,*ff,*FF,d;
    357:   PetscInt       i,M,xs,xm;
    358:   Vec            xlocal;

    361:   DMGetLocalVector(da,&xlocal);
    362:   /*
    363:      Scatter ghost points to local vector, using the 2-step process
    364:         DMGlobalToLocalBegin(), DMGlobalToLocalEnd().
    365:      By placing code between these two statements, computations can
    366:      be done while messages are in transition.
    367:   */
    368:   DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
    369:   DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);

    371:   /*
    372:      Get pointers to vector data.
    373:        - The vector xlocal includes ghost point; the vectors x and f do
    374:          NOT include ghost points.
    375:        - Using DMDAVecGetArray() allows accessing the values using global ordering
    376:   */
    377:   DMDAVecGetArray(da,xlocal,&xx);
    378:   DMDAVecGetArray(da,f,&ff);
    379:   DMDAVecGetArray(da,user->F,&FF);

    381:   /*
    382:      Get local grid boundaries (for 1-dimensional DMDA):
    383:        xs, xm  - starting grid index, width of local grid (no ghost points)
    384:   */
    385:   DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);
    386:   DMDAGetInfo(da,NULL,&M,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);

    388:   /*
    389:      Set function values for boundary points; define local interior grid point range:
    390:         xsi - starting interior grid index
    391:         xei - ending interior grid index
    392:   */
    393:   if (xs == 0) { /* left boundary */
    394:     ff[0] = xx[0];
    395:     xs++;xm--;
    396:   }
    397:   if (xs+xm == M) {  /* right boundary */
    398:     ff[xs+xm-1] = xx[xs+xm-1] - 1.0;
    399:     xm--;
    400:   }

    402:   /*
    403:      Compute function over locally owned part of the grid (interior points only)
    404:   */
    405:   d = 1.0/(user->h*user->h);
    406:   for (i=xs; i<xs+xm; i++) ff[i] = d*(xx[i-1] - 2.0*xx[i] + xx[i+1]) + xx[i]*xx[i] - FF[i];

    408:   /*
    409:      Restore vectors
    410:   */
    411:   DMDAVecRestoreArray(da,xlocal,&xx);
    412:   DMDAVecRestoreArray(da,f,&ff);
    413:   DMDAVecRestoreArray(da,user->F,&FF);
    414:   DMRestoreLocalVector(da,&xlocal);
    415:   return(0);
    416: }

    418: /* ------------------------------------------------------------------- */
    419: /*
    420:    FormJacobian - Evaluates Jacobian matrix.

    422:    Input Parameters:
    423: .  snes - the SNES context
    424: .  x - input vector
    425: .  dummy - optional user-defined context (not used here)

    427:    Output Parameters:
    428: .  jac - Jacobian matrix
    429: .  B - optionally different preconditioning matrix
    430: .  flag - flag indicating matrix structure
    431: */
    432: PetscErrorCode FormJacobian(SNES snes,Vec x,Mat jac,Mat B,void *ctx)
    433: {
    434:   ApplicationCtx *user = (ApplicationCtx*) ctx;
    435:   PetscScalar    *xx,d,A[3];
    437:   PetscInt       i,j[3],M,xs,xm;
    438:   DM             da = user->da;

    441:   if (user->sjerr) {
    442:     SNESSetJacobianDomainError(snes);
    443:     return(0);
    444:   }
    445:   /*
    446:      Get pointer to vector data
    447:   */
    448:   DMDAVecGetArrayRead(da,x,&xx);
    449:   DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

    451:   /*
    452:     Get range of locally owned matrix
    453:   */
    454:   DMDAGetInfo(da,NULL,&M,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);

    456:   /*
    457:      Determine starting and ending local indices for interior grid points.
    458:      Set Jacobian entries for boundary points.
    459:   */

    461:   if (xs == 0) {  /* left boundary */
    462:     i = 0; A[0] = 1.0;

    464:     MatSetValues(jac,1,&i,1,&i,A,INSERT_VALUES);
    465:     xs++;xm--;
    466:   }
    467:   if (xs+xm == M) { /* right boundary */
    468:     i    = M-1;
    469:     A[0] = 1.0;
    470:     MatSetValues(jac,1,&i,1,&i,A,INSERT_VALUES);
    471:     xm--;
    472:   }

    474:   /*
    475:      Interior grid points
    476:       - Note that in this case we set all elements for a particular
    477:         row at once.
    478:   */
    479:   d = 1.0/(user->h*user->h);
    480:   for (i=xs; i<xs+xm; i++) {
    481:     j[0] = i - 1; j[1] = i; j[2] = i + 1;
    482:     A[0] = A[2] = d; A[1] = -2.0*d + 2.0*xx[i];
    483:     MatSetValues(jac,1,&i,3,j,A,INSERT_VALUES);
    484:   }

    486:   /*
    487:      Assemble matrix, using the 2-step process:
    488:        MatAssemblyBegin(), MatAssemblyEnd().
    489:      By placing code between these two statements, computations can be
    490:      done while messages are in transition.

    492:      Also, restore vector.
    493:   */

    495:   MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
    496:   DMDAVecRestoreArrayRead(da,x,&xx);
    497:   MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);

    499:   return(0);
    500: }

    502: /* ------------------------------------------------------------------- */
    503: /*
    504:    Monitor - Optional user-defined monitoring routine that views the
    505:    current iterate with an x-window plot. Set by SNESMonitorSet().

    507:    Input Parameters:
    508:    snes - the SNES context
    509:    its - iteration number
    510:    norm - 2-norm function value (may be estimated)
    511:    ctx - optional user-defined context for private data for the
    512:          monitor routine, as set by SNESMonitorSet()

    514:    Note:
    515:    See the manpage for PetscViewerDrawOpen() for useful runtime options,
    516:    such as -nox to deactivate all x-window output.
    517:  */
    518: PetscErrorCode Monitor(SNES snes,PetscInt its,PetscReal fnorm,void *ctx)
    519: {
    521:   MonitorCtx     *monP = (MonitorCtx*) ctx;
    522:   Vec            x;

    525:   PetscPrintf(PETSC_COMM_WORLD,"iter = %D,SNES Function norm %g\n",its,(double)fnorm);
    526:   SNESGetSolution(snes,&x);
    527:   VecView(x,monP->viewer);
    528:   return(0);
    529: }

    531: /* ------------------------------------------------------------------- */
    532: /*
    533:    PreCheck - Optional user-defined routine that checks the validity of
    534:    candidate steps of a line search method.  Set by SNESLineSearchSetPreCheck().

    536:    Input Parameters:
    537:    snes - the SNES context
    538:    xcurrent - current solution
    539:    y - search direction and length

    541:    Output Parameters:
    542:    y         - proposed step (search direction and length) (possibly changed)
    543:    changed_y - tells if the step has changed or not
    544:  */
    545: PetscErrorCode PreCheck(SNESLineSearch linesearch,Vec xcurrent,Vec y, PetscBool *changed_y, void * ctx)
    546: {
    548:   *changed_y = PETSC_FALSE;
    549:   return(0);
    550: }

    552: /* ------------------------------------------------------------------- */
    553: /*
    554:    PostCheck - Optional user-defined routine that checks the validity of
    555:    candidate steps of a line search method.  Set by SNESLineSearchSetPostCheck().

    557:    Input Parameters:
    558:    snes - the SNES context
    559:    ctx  - optional user-defined context for private data for the
    560:           monitor routine, as set by SNESLineSearchSetPostCheck()
    561:    xcurrent - current solution
    562:    y - search direction and length
    563:    x    - the new candidate iterate

    565:    Output Parameters:
    566:    y    - proposed step (search direction and length) (possibly changed)
    567:    x    - current iterate (possibly modified)

    569:  */
    570: PetscErrorCode PostCheck(SNESLineSearch linesearch,Vec xcurrent,Vec y,Vec x,PetscBool  *changed_y,PetscBool  *changed_x, void * ctx)
    571: {
    573:   PetscInt       i,iter,xs,xm;
    574:   StepCheckCtx   *check;
    575:   ApplicationCtx *user;
    576:   PetscScalar    *xa,*xa_last,tmp;
    577:   PetscReal      rdiff;
    578:   DM             da;
    579:   SNES           snes;

    582:   *changed_x = PETSC_FALSE;
    583:   *changed_y = PETSC_FALSE;

    585:   SNESLineSearchGetSNES(linesearch, &snes);
    586:   check = (StepCheckCtx*)ctx;
    587:   user  = check->user;
    588:   SNESGetIterationNumber(snes,&iter);

    590:   /* iteration 1 indicates we are working on the second iteration */
    591:   if (iter > 0) {
    592:     da   = user->da;
    593:     PetscPrintf(PETSC_COMM_WORLD,"Checking candidate step at iteration %D with tolerance %g\n",iter,(double)check->tolerance);

    595:     /* Access local array data */
    596:     DMDAVecGetArray(da,check->last_step,&xa_last);
    597:     DMDAVecGetArray(da,x,&xa);
    598:     DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

    600:     /*
    601:        If we fail the user-defined check for validity of the candidate iterate,
    602:        then modify the iterate as we like.  (Note that the particular modification
    603:        below is intended simply to demonstrate how to manipulate this data, not
    604:        as a meaningful or appropriate choice.)
    605:     */
    606:     for (i=xs; i<xs+xm; i++) {
    607:       if (!PetscAbsScalar(xa[i])) rdiff = 2*check->tolerance;
    608:       else rdiff = PetscAbsScalar((xa[i] - xa_last[i])/xa[i]);
    609:       if (rdiff > check->tolerance) {
    610:         tmp        = xa[i];
    611:         xa[i]      = .5*(xa[i] + xa_last[i]);
    612:         *changed_x = PETSC_TRUE;
    613:         PetscPrintf(PETSC_COMM_WORLD,"  Altering entry %D: x=%g, x_last=%g, diff=%g, x_new=%g\n",i,(double)PetscAbsScalar(tmp),(double)PetscAbsScalar(xa_last[i]),(double)rdiff,(double)PetscAbsScalar(xa[i]));
    614:       }
    615:     }
    616:     DMDAVecRestoreArray(da,check->last_step,&xa_last);
    617:     DMDAVecRestoreArray(da,x,&xa);
    618:   }
    619:   VecCopy(x,check->last_step);
    620:   return(0);
    621: }

    623: /* ------------------------------------------------------------------- */
    624: /*
    625:    PostSetSubKSP - Optional user-defined routine that reset SubKSP options when hierarchical bjacobi PC is used
    626:    e.g,
    627:      mpiexec -n 8 ./ex3 -nox -n 10000 -ksp_type fgmres -pc_type bjacobi -pc_bjacobi_blocks 4 -sub_ksp_type gmres -sub_ksp_max_it 3 -post_setsubksp -sub_ksp_rtol 1.e-16
    628:    Set by SNESLineSearchSetPostCheck().

    630:    Input Parameters:
    631:    linesearch - the LineSearch context
    632:    xcurrent - current solution
    633:    y - search direction and length
    634:    x    - the new candidate iterate

    636:    Output Parameters:
    637:    y    - proposed step (search direction and length) (possibly changed)
    638:    x    - current iterate (possibly modified)

    640:  */
    641: PetscErrorCode PostSetSubKSP(SNESLineSearch linesearch,Vec xcurrent,Vec y,Vec x,PetscBool  *changed_y,PetscBool  *changed_x, void * ctx)
    642: {
    644:   SetSubKSPCtx   *check;
    645:   PetscInt       iter,its,sub_its,maxit;
    646:   KSP            ksp,sub_ksp,*sub_ksps;
    647:   PC             pc;
    648:   PetscReal      ksp_ratio;
    649:   SNES           snes;

    652:   SNESLineSearchGetSNES(linesearch, &snes);
    653:   check   = (SetSubKSPCtx*)ctx;
    654:   SNESGetIterationNumber(snes,&iter);
    655:   SNESGetKSP(snes,&ksp);
    656:   KSPGetPC(ksp,&pc);
    657:   PCBJacobiGetSubKSP(pc,NULL,NULL,&sub_ksps);
    658:   sub_ksp = sub_ksps[0];
    659:   KSPGetIterationNumber(ksp,&its);      /* outer KSP iteration number */
    660:   KSPGetIterationNumber(sub_ksp,&sub_its); /* inner KSP iteration number */

    662:   if (iter) {
    663:     PetscPrintf(PETSC_COMM_WORLD,"    ...PostCheck snes iteration %D, ksp_it %D %D, subksp_it %D\n",iter,check->its0,its,sub_its);
    664:     ksp_ratio = ((PetscReal)(its))/check->its0;
    665:     maxit     = (PetscInt)(ksp_ratio*sub_its + 0.5);
    666:     if (maxit < 2) maxit = 2;
    667:     KSPSetTolerances(sub_ksp,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT,maxit);
    668:     PetscPrintf(PETSC_COMM_WORLD,"    ...ksp_ratio %g, new maxit %D\n\n",(double)ksp_ratio,maxit);
    669:   }
    670:   check->its0 = its; /* save current outer KSP iteration number */
    671:   return(0);
    672: }

    674: /* ------------------------------------------------------------------- */
    675: /*
    676:    MatrixFreePreconditioner - This routine demonstrates the use of a
    677:    user-provided preconditioner.  This code implements just the null
    678:    preconditioner, which of course is not recommended for general use.

    680:    Input Parameters:
    681: +  pc - preconditioner
    682: -  x - input vector

    684:    Output Parameter:
    685: .  y - preconditioned vector
    686: */
    687: PetscErrorCode MatrixFreePreconditioner(PC pc,Vec x,Vec y)
    688: {
    690:   VecCopy(x,y);
    691:   return 0;
    692: }

    695: /*TEST

    697:    test:
    698:       args: -nox -snes_monitor_cancel -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always

    700:    test:
    701:       suffix: 2
    702:       nsize: 3
    703:       args: -nox -pc_type asm -mat_type mpiaij -snes_monitor_cancel -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always

    705:    test:
    706:       suffix: 3
    707:       nsize: 2
    708:       args: -nox -snes_monitor_cancel -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always

    710:    test:
    711:       suffix: 4
    712:       args: -nox -pre_check_iterates -post_check_iterates

    714:    test:
    715:       suffix: 5
    716:       requires: double !complex !single
    717:       nsize: 2
    718:       args: -nox -snes_test_jacobian  -snes_test_jacobian_view

    720:    test:
    721:       suffix: 6
    722:       requires: double !complex !single
    723:       nsize: 4
    724:       args: -test_jacobian_domain_error -snes_converged_reason -snes_check_jacobian_domain_error 1

    726:    test:
    727:       suffix: 7
    728:       requires: double !complex !single
    729:       nsize: 4
    730:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type newtontr -snes_check_jacobian_domain_error 1

    732:    test:
    733:       suffix: 8
    734:       requires: double !complex !single
    735:       nsize: 4
    736:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type vinewtonrsls -snes_check_jacobian_domain_error 1

    738:    test:
    739:       suffix: 9
    740:       requires: double !complex !single
    741:       nsize: 4
    742:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type vinewtonssls -snes_check_jacobian_domain_error 1

    744:    test:
    745:       suffix: 10
    746:       requires: double !complex !single
    747:       nsize: 4
    748:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type qn -snes_qn_scale_type jacobian -snes_check_jacobian_domain_error 1

    750:    test:
    751:       suffix: 11
    752:       requires: double !complex !single
    753:       nsize: 4
    754:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type ms -snes_check_jacobian_domain_error 1

    756: TEST*/