Actual source code: ex3.c
petsc-3.15.0 2021-03-30
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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 application 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,viewinitial = PETSC_FALSE;

    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);
    107:   PetscOptionsGetBool(NULL,NULL,"-view_initial",&viewinitial,NULL);

    109:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    110:      Create nonlinear solver context
    111:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    113:   SNESCreate(PETSC_COMM_WORLD,&snes);

    115:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    116:      Create vector data structures; set function evaluation routine
    117:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

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

    145:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    146:      Create matrix data structure; set Jacobian evaluation routine
    147:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

    165:   /*
    166:      Optionally allow user-provided preconditioner
    167:    */
    168:   PetscOptionsHasName(NULL,NULL,"-user_precond",&flg);
    169:   if (flg) {
    170:     KSP ksp;
    171:     PC  pc;
    172:     SNESGetKSP(snes,&ksp);
    173:     KSPGetPC(ksp,&pc);
    174:     PCSetType(pc,PCSHELL);
    175:     PCShellSetApply(pc,MatrixFreePreconditioner);
    176:   }

    178:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    179:      Customize nonlinear solver; set runtime options
    180:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

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

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

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

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

    215:     PetscOptionsGetReal(NULL,NULL,"-check_tol",&checkP.tolerance,NULL);
    216:   }

    218:   PetscOptionsHasName(NULL,NULL,"-post_setsubksp",&post_setsubksp);
    219:   if (post_setsubksp) {
    220:     PetscPrintf(PETSC_COMM_WORLD,"Activating post setsubksp\n");
    221:     SNESLineSearchSetPostCheck(linesearch,PostSetSubKSP,&checkP1);
    222:   }

    224:   PetscOptionsHasName(NULL,NULL,"-pre_check_iterates",&pre_check);
    225:   if (pre_check) {
    226:     PetscPrintf(PETSC_COMM_WORLD,"Activating pre step checking routine\n");
    227:     SNESLineSearchSetPreCheck(linesearch,PreCheck,&checkP);
    228:   }

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

    238:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    239:      Initialize application:
    240:      Store right-hand-side of PDE and exact solution
    241:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

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

    255:   /*
    256:      Compute local vector entries
    257:   */
    258:   xp = ctx.h*xs;
    259:   for (i=xs; i<xs+xm; i++) {
    260:     FF[i] = 6.0*xp + PetscPowScalar(xp+1.e-12,6.0); /* +1.e-12 is to prevent 0^6 */
    261:     UU[i] = xp*xp*xp;
    262:     xp   += ctx.h;
    263:   }

    265:   /*
    266:      Restore vectors
    267:   */
    268:   DMDAVecRestoreArray(ctx.da,F,&FF);
    269:   DMDAVecRestoreArray(ctx.da,U,&UU);
    270:   if (viewinitial) {
    271:     VecView(U,0);
    272:     VecView(F,0);
    273:   }

    275:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    276:      Evaluate initial guess; then solve nonlinear system
    277:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    279:   /*
    280:      Note: The user should initialize the vector, x, with the initial guess
    281:      for the nonlinear solver prior to calling SNESSolve().  In particular,
    282:      to employ an initial guess of zero, the user should explicitly set
    283:      this vector to zero by calling VecSet().
    284:   */
    285:   FormInitialGuess(x);
    286:   SNESSolve(snes,NULL,x);
    287:   SNESGetIterationNumber(snes,&its);
    288:   PetscPrintf(PETSC_COMM_WORLD,"Number of SNES iterations = %D\n",its);

    290:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    291:      Check solution and clean up
    292:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    294:   /*
    295:      Check the error
    296:   */
    297:   VecAXPY(x,none,U);
    298:   VecNorm(x,NORM_2,&norm);
    299:   PetscPrintf(PETSC_COMM_WORLD,"Norm of error %g Iterations %D\n",(double)norm,its);
    300:   if (ctx.sjerr) {
    301:     SNESType       snestype;
    302:     SNESGetType(snes,&snestype);
    303:     PetscPrintf(PETSC_COMM_WORLD,"SNES Type %s\n",snestype);
    304:   }

    306:   /*
    307:      Free work space.  All PETSc objects should be destroyed when they
    308:      are no longer needed.
    309:   */
    310:   PetscViewerDestroy(&monP.viewer);
    311:   if (post_check) {VecDestroy(&checkP.last_step);}
    312:   VecDestroy(&x);
    313:   VecDestroy(&r);
    314:   VecDestroy(&U);
    315:   VecDestroy(&F);
    316:   MatDestroy(&J);
    317:   SNESDestroy(&snes);
    318:   DMDestroy(&ctx.da);
    319:   PetscFinalize();
    320:   return ierr;
    321: }

    323: /* ------------------------------------------------------------------- */
    324: /*
    325:    FormInitialGuess - Computes initial guess.

    327:    Input/Output Parameter:
    328: .  x - the solution vector
    329: */
    330: PetscErrorCode FormInitialGuess(Vec x)
    331: {
    333:   PetscScalar    pfive = .50;

    336:   VecSet(x,pfive);
    337:   return(0);
    338: }

    340: /* ------------------------------------------------------------------- */
    341: /*
    342:    FormFunction - Evaluates nonlinear function, F(x).

    344:    Input Parameters:
    345: .  snes - the SNES context
    346: .  x - input vector
    347: .  ctx - optional user-defined context, as set by SNESSetFunction()

    349:    Output Parameter:
    350: .  f - function vector

    352:    Note:
    353:    The user-defined context can contain any application-specific
    354:    data needed for the function evaluation.
    355: */
    356: PetscErrorCode FormFunction(SNES snes,Vec x,Vec f,void *ctx)
    357: {
    358:   ApplicationCtx *user = (ApplicationCtx*) ctx;
    359:   DM             da    = user->da;
    360:   PetscScalar    *xx,*ff,*FF,d;
    362:   PetscInt       i,M,xs,xm;
    363:   Vec            xlocal;

    366:   DMGetLocalVector(da,&xlocal);
    367:   /*
    368:      Scatter ghost points to local vector, using the 2-step process
    369:         DMGlobalToLocalBegin(), DMGlobalToLocalEnd().
    370:      By placing code between these two statements, computations can
    371:      be done while messages are in transition.
    372:   */
    373:   DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
    374:   DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);

    376:   /*
    377:      Get pointers to vector data.
    378:        - The vector xlocal includes ghost point; the vectors x and f do
    379:          NOT include ghost points.
    380:        - Using DMDAVecGetArray() allows accessing the values using global ordering
    381:   */
    382:   DMDAVecGetArray(da,xlocal,&xx);
    383:   DMDAVecGetArray(da,f,&ff);
    384:   DMDAVecGetArray(da,user->F,&FF);

    386:   /*
    387:      Get local grid boundaries (for 1-dimensional DMDA):
    388:        xs, xm  - starting grid index, width of local grid (no ghost points)
    389:   */
    390:   DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);
    391:   DMDAGetInfo(da,NULL,&M,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);

    393:   /*
    394:      Set function values for boundary points; define local interior grid point range:
    395:         xsi - starting interior grid index
    396:         xei - ending interior grid index
    397:   */
    398:   if (xs == 0) { /* left boundary */
    399:     ff[0] = xx[0];
    400:     xs++;xm--;
    401:   }
    402:   if (xs+xm == M) {  /* right boundary */
    403:     ff[xs+xm-1] = xx[xs+xm-1] - 1.0;
    404:     xm--;
    405:   }

    407:   /*
    408:      Compute function over locally owned part of the grid (interior points only)
    409:   */
    410:   d = 1.0/(user->h*user->h);
    411:   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];

    413:   /*
    414:      Restore vectors
    415:   */
    416:   DMDAVecRestoreArray(da,xlocal,&xx);
    417:   DMDAVecRestoreArray(da,f,&ff);
    418:   DMDAVecRestoreArray(da,user->F,&FF);
    419:   DMRestoreLocalVector(da,&xlocal);
    420:   return(0);
    421: }

    423: /* ------------------------------------------------------------------- */
    424: /*
    425:    FormJacobian - Evaluates Jacobian matrix.

    427:    Input Parameters:
    428: .  snes - the SNES context
    429: .  x - input vector
    430: .  dummy - optional user-defined context (not used here)

    432:    Output Parameters:
    433: .  jac - Jacobian matrix
    434: .  B - optionally different preconditioning matrix
    435: .  flag - flag indicating matrix structure
    436: */
    437: PetscErrorCode FormJacobian(SNES snes,Vec x,Mat jac,Mat B,void *ctx)
    438: {
    439:   ApplicationCtx *user = (ApplicationCtx*) ctx;
    440:   PetscScalar    *xx,d,A[3];
    442:   PetscInt       i,j[3],M,xs,xm;
    443:   DM             da = user->da;

    446:   if (user->sjerr) {
    447:     SNESSetJacobianDomainError(snes);
    448:     return(0);
    449:   }
    450:   /*
    451:      Get pointer to vector data
    452:   */
    453:   DMDAVecGetArrayRead(da,x,&xx);
    454:   DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

    456:   /*
    457:     Get range of locally owned matrix
    458:   */
    459:   DMDAGetInfo(da,NULL,&M,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);

    461:   /*
    462:      Determine starting and ending local indices for interior grid points.
    463:      Set Jacobian entries for boundary points.
    464:   */

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

    469:     MatSetValues(jac,1,&i,1,&i,A,INSERT_VALUES);
    470:     xs++;xm--;
    471:   }
    472:   if (xs+xm == M) { /* right boundary */
    473:     i    = M-1;
    474:     A[0] = 1.0;
    475:     MatSetValues(jac,1,&i,1,&i,A,INSERT_VALUES);
    476:     xm--;
    477:   }

    479:   /*
    480:      Interior grid points
    481:       - Note that in this case we set all elements for a particular
    482:         row at once.
    483:   */
    484:   d = 1.0/(user->h*user->h);
    485:   for (i=xs; i<xs+xm; i++) {
    486:     j[0] = i - 1; j[1] = i; j[2] = i + 1;
    487:     A[0] = A[2] = d; A[1] = -2.0*d + 2.0*xx[i];
    488:     MatSetValues(jac,1,&i,3,j,A,INSERT_VALUES);
    489:   }

    491:   /*
    492:      Assemble matrix, using the 2-step process:
    493:        MatAssemblyBegin(), MatAssemblyEnd().
    494:      By placing code between these two statements, computations can be
    495:      done while messages are in transition.

    497:      Also, restore vector.
    498:   */

    500:   MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
    501:   DMDAVecRestoreArrayRead(da,x,&xx);
    502:   MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);

    504:   return(0);
    505: }

    507: /* ------------------------------------------------------------------- */
    508: /*
    509:    Monitor - Optional user-defined monitoring routine that views the
    510:    current iterate with an x-window plot. Set by SNESMonitorSet().

    512:    Input Parameters:
    513:    snes - the SNES context
    514:    its - iteration number
    515:    norm - 2-norm function value (may be estimated)
    516:    ctx - optional user-defined context for private data for the
    517:          monitor routine, as set by SNESMonitorSet()

    519:    Note:
    520:    See the manpage for PetscViewerDrawOpen() for useful runtime options,
    521:    such as -nox to deactivate all x-window output.
    522:  */
    523: PetscErrorCode Monitor(SNES snes,PetscInt its,PetscReal fnorm,void *ctx)
    524: {
    526:   MonitorCtx     *monP = (MonitorCtx*) ctx;
    527:   Vec            x;

    530:   PetscPrintf(PETSC_COMM_WORLD,"iter = %D,SNES Function norm %g\n",its,(double)fnorm);
    531:   SNESGetSolution(snes,&x);
    532:   VecView(x,monP->viewer);
    533:   return(0);
    534: }

    536: /* ------------------------------------------------------------------- */
    537: /*
    538:    PreCheck - Optional user-defined routine that checks the validity of
    539:    candidate steps of a line search method.  Set by SNESLineSearchSetPreCheck().

    541:    Input Parameters:
    542:    snes - the SNES context
    543:    xcurrent - current solution
    544:    y - search direction and length

    546:    Output Parameters:
    547:    y         - proposed step (search direction and length) (possibly changed)
    548:    changed_y - tells if the step has changed or not
    549:  */
    550: PetscErrorCode PreCheck(SNESLineSearch linesearch,Vec xcurrent,Vec y, PetscBool *changed_y, void * ctx)
    551: {
    553:   *changed_y = PETSC_FALSE;
    554:   return(0);
    555: }

    557: /* ------------------------------------------------------------------- */
    558: /*
    559:    PostCheck - Optional user-defined routine that checks the validity of
    560:    candidate steps of a line search method.  Set by SNESLineSearchSetPostCheck().

    562:    Input Parameters:
    563:    snes - the SNES context
    564:    ctx  - optional user-defined context for private data for the
    565:           monitor routine, as set by SNESLineSearchSetPostCheck()
    566:    xcurrent - current solution
    567:    y - search direction and length
    568:    x    - the new candidate iterate

    570:    Output Parameters:
    571:    y    - proposed step (search direction and length) (possibly changed)
    572:    x    - current iterate (possibly modified)

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

    587:   *changed_x = PETSC_FALSE;
    588:   *changed_y = PETSC_FALSE;

    590:   SNESLineSearchGetSNES(linesearch, &snes);
    591:   check = (StepCheckCtx*)ctx;
    592:   user  = check->user;
    593:   SNESGetIterationNumber(snes,&iter);

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

    600:     /* Access local array data */
    601:     DMDAVecGetArray(da,check->last_step,&xa_last);
    602:     DMDAVecGetArray(da,x,&xa);
    603:     DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

    605:     /*
    606:        If we fail the user-defined check for validity of the candidate iterate,
    607:        then modify the iterate as we like.  (Note that the particular modification
    608:        below is intended simply to demonstrate how to manipulate this data, not
    609:        as a meaningful or appropriate choice.)
    610:     */
    611:     for (i=xs; i<xs+xm; i++) {
    612:       if (!PetscAbsScalar(xa[i])) rdiff = 2*check->tolerance;
    613:       else rdiff = PetscAbsScalar((xa[i] - xa_last[i])/xa[i]);
    614:       if (rdiff > check->tolerance) {
    615:         tmp        = xa[i];
    616:         xa[i]      = .5*(xa[i] + xa_last[i]);
    617:         *changed_x = PETSC_TRUE;
    618:         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]));
    619:       }
    620:     }
    621:     DMDAVecRestoreArray(da,check->last_step,&xa_last);
    622:     DMDAVecRestoreArray(da,x,&xa);
    623:   }
    624:   VecCopy(x,check->last_step);
    625:   return(0);
    626: }

    628: /* ------------------------------------------------------------------- */
    629: /*
    630:    PostSetSubKSP - Optional user-defined routine that reset SubKSP options when hierarchical bjacobi PC is used
    631:    e.g,
    632:      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
    633:    Set by SNESLineSearchSetPostCheck().

    635:    Input Parameters:
    636:    linesearch - the LineSearch context
    637:    xcurrent - current solution
    638:    y - search direction and length
    639:    x    - the new candidate iterate

    641:    Output Parameters:
    642:    y    - proposed step (search direction and length) (possibly changed)
    643:    x    - current iterate (possibly modified)

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

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

    667:   if (iter) {
    668:     PetscPrintf(PETSC_COMM_WORLD,"    ...PostCheck snes iteration %D, ksp_it %D %D, subksp_it %D\n",iter,check->its0,its,sub_its);
    669:     ksp_ratio = ((PetscReal)(its))/check->its0;
    670:     maxit     = (PetscInt)(ksp_ratio*sub_its + 0.5);
    671:     if (maxit < 2) maxit = 2;
    672:     KSPSetTolerances(sub_ksp,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT,maxit);
    673:     PetscPrintf(PETSC_COMM_WORLD,"    ...ksp_ratio %g, new maxit %D\n\n",(double)ksp_ratio,maxit);
    674:   }
    675:   check->its0 = its; /* save current outer KSP iteration number */
    676:   return(0);
    677: }

    679: /* ------------------------------------------------------------------- */
    680: /*
    681:    MatrixFreePreconditioner - This routine demonstrates the use of a
    682:    user-provided preconditioner.  This code implements just the null
    683:    preconditioner, which of course is not recommended for general use.

    685:    Input Parameters:
    686: +  pc - preconditioner
    687: -  x - input vector

    689:    Output Parameter:
    690: .  y - preconditioned vector
    691: */
    692: PetscErrorCode MatrixFreePreconditioner(PC pc,Vec x,Vec y)
    693: {
    695:   VecCopy(x,y);
    696:   return 0;
    697: }

    700: /*TEST

    702:    test:
    703:       args: -nox -snes_monitor_cancel -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always

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

    710:    test:
    711:       suffix: 3
    712:       nsize: 2
    713:       args: -nox -snes_monitor_cancel -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always

    715:    test:
    716:       suffix: 4
    717:       args: -nox -pre_check_iterates -post_check_iterates

    719:    test:
    720:       suffix: 5
    721:       requires: double !complex !single
    722:       nsize: 2
    723:       args: -nox -snes_test_jacobian  -snes_test_jacobian_view

    725:    test:
    726:       suffix: 6
    727:       requires: double !complex !single
    728:       nsize: 4
    729:       args: -test_jacobian_domain_error -snes_converged_reason -snes_check_jacobian_domain_error 1

    731:    test:
    732:       suffix: 7
    733:       requires: double !complex !single
    734:       nsize: 4
    735:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type newtontr -snes_check_jacobian_domain_error 1

    737:    test:
    738:       suffix: 8
    739:       requires: double !complex !single
    740:       nsize: 4
    741:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type vinewtonrsls -snes_check_jacobian_domain_error 1

    743:    test:
    744:       suffix: 9
    745:       requires: double !complex !single
    746:       nsize: 4
    747:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type vinewtonssls -snes_check_jacobian_domain_error 1

    749:    test:
    750:       suffix: 10
    751:       requires: double !complex !single
    752:       nsize: 4
    753:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type qn -snes_qn_scale_type jacobian -snes_check_jacobian_domain_error 1

    755:    test:
    756:       suffix: 11
    757:       requires: double !complex !single
    758:       nsize: 4
    759:       args: -test_jacobian_domain_error -snes_converged_reason -snes_type ms -snes_ms_type m62 -snes_ms_damping 0.9 -snes_check_jacobian_domain_error 1

    761:    test:
    762:       suffix: 12
    763:       args: -view_initial
    764:       filter: grep -v "type:"

    766: TEST*/