Date: 2016-07-24T17:16:06+00:00

Actual source code: armijo.c
petsc-3.7.3 2016-07-24
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      1: #include <petsc/private/taolinesearchimpl.h>
      2: #include <../src/tao/linesearch/impls/armijo/armijo.h>

      4: #define REPLACE_FIFO 1
      5: #define REPLACE_MRU  2

      7: #define REFERENCE_MAX  1
      8: #define REFERENCE_AVE  2
      9: #define REFERENCE_MEAN 3

     13: static PetscErrorCode TaoLineSearchDestroy_Armijo(TaoLineSearch ls)
     14: {
     15:   TaoLineSearch_ARMIJO *armP = (TaoLineSearch_ARMIJO *)ls->data;
     16:   PetscErrorCode       ierr;

     19:   PetscFree(armP->memory);
     20:   VecDestroy(&armP->x);
     21:   VecDestroy(&armP->work);
     22:   PetscFree(ls->data);
     23:   return(0);
     24: }

     28: static PetscErrorCode TaoLineSearchReset_Armijo(TaoLineSearch ls)
     29: {
     30:   TaoLineSearch_ARMIJO *armP = (TaoLineSearch_ARMIJO *)ls->data;
     31:   PetscErrorCode       ierr;

     34:   PetscFree(armP->memory);
     35:   armP->memorySetup = PETSC_FALSE;
     36:   return(0);
     37: }

     41: static PetscErrorCode TaoLineSearchSetFromOptions_Armijo(PetscOptionItems *PetscOptionsObject,TaoLineSearch ls)
     42: {
     43:   TaoLineSearch_ARMIJO *armP = (TaoLineSearch_ARMIJO *)ls->data;
     44:   PetscErrorCode       ierr;

     47:   PetscOptionsHead(PetscOptionsObject,"Armijo linesearch options");
     48:   PetscOptionsReal("-tao_ls_armijo_alpha", "initial reference constant", "", armP->alpha, &armP->alpha,NULL);
     49:   PetscOptionsReal("-tao_ls_armijo_beta_inf", "decrease constant one", "", armP->beta_inf, &armP->beta_inf,NULL);
     50:   PetscOptionsReal("-tao_ls_armijo_beta", "decrease constant", "", armP->beta, &armP->beta,NULL);
     51:   PetscOptionsReal("-tao_ls_armijo_sigma", "acceptance constant", "", armP->sigma, &armP->sigma,NULL);
     52:   PetscOptionsInt("-tao_ls_armijo_memory_size", "number of historical elements", "", armP->memorySize, &armP->memorySize,NULL);
     53:   PetscOptionsInt("-tao_ls_armijo_reference_policy", "policy for updating reference value", "", armP->referencePolicy, &armP->referencePolicy,NULL);
     54:   PetscOptionsInt("-tao_ls_armijo_replacement_policy", "policy for updating memory", "", armP->replacementPolicy, &armP->replacementPolicy,NULL);
     55:   PetscOptionsBool("-tao_ls_armijo_nondescending","Use nondescending armijo algorithm","",armP->nondescending,&armP->nondescending,NULL);
     56:   PetscOptionsTail();
     57:   return(0);
     58: }

     62: static PetscErrorCode TaoLineSearchView_Armijo(TaoLineSearch ls, PetscViewer pv)
     63: {
     64:   TaoLineSearch_ARMIJO *armP = (TaoLineSearch_ARMIJO *)ls->data;
     65:   PetscBool            isascii;
     66:   PetscErrorCode       ierr;

     69:   PetscObjectTypeCompare((PetscObject)pv, PETSCVIEWERASCII, &isascii);
     70:   if (isascii) {
     71:     ierr=PetscViewerASCIIPrintf(pv,"  Armijo linesearch",armP->alpha);
     72:     if (armP->nondescending) {
     73:       PetscViewerASCIIPrintf(pv, " (nondescending)");
     74:     }
     75:     if (ls->bounded) {
     76:       PetscViewerASCIIPrintf(pv," (projected)");
     77:     }
     78:     ierr=PetscViewerASCIIPrintf(pv,": alpha=%g beta=%g ",(double)armP->alpha,(double)armP->beta);
     79:     ierr=PetscViewerASCIIPrintf(pv,"sigma=%g ",(double)armP->sigma);
     80:     ierr=PetscViewerASCIIPrintf(pv,"memsize=%D\n",armP->memorySize);
     81:   }
     82:   return(0);
     83: }

     87: /* @ TaoApply_Armijo - This routine performs a linesearch. It
     88:    backtracks until the (nonmonotone) Armijo conditions are satisfied.

     90:    Input Parameters:
     91: +  tao - Tao context
     92: .  X - current iterate (on output X contains new iterate, X + step*S)
     93: .  S - search direction
     94: .  f - merit function evaluated at X
     95: .  G - gradient of merit function evaluated at X
     96: .  W - work vector
     97: -  step - initial estimate of step length

     99:    Output parameters:
    100: +  f - merit function evaluated at new iterate, X + step*S
    101: .  G - gradient of merit function evaluated at new iterate, X + step*S
    102: .  X - new iterate
    103: -  step - final step length

    105: @ */
    106: static PetscErrorCode TaoLineSearchApply_Armijo(TaoLineSearch ls, Vec x, PetscReal *f, Vec g, Vec s)
    107: {
    108:   TaoLineSearch_ARMIJO *armP = (TaoLineSearch_ARMIJO *)ls->data;
    109:   PetscErrorCode       ierr;
    110:   PetscInt             i;
    111:   PetscReal            fact, ref, gdx;
    112:   PetscInt             idx;
    113:   PetscBool            g_computed=PETSC_FALSE; /* to prevent extra gradient computation */

    117:   ls->reason = TAOLINESEARCH_CONTINUE_ITERATING;
    118:   if (!armP->work) {
    119:     VecDuplicate(x,&armP->work);
    120:     armP->x = x;
    121:     PetscObjectReference((PetscObject)armP->x);
    122:   } else if (x != armP->x) {
    123:     /* If x has changed, then recreate work */
    124:     VecDestroy(&armP->work);
    125:     VecDuplicate(x,&armP->work);
    126:     PetscObjectDereference((PetscObject)armP->x);
    127:     armP->x = x;
    128:     PetscObjectReference((PetscObject)armP->x);
    129:   }

    131:   /* Check linesearch parameters */
    132:   if (armP->alpha < 1) {
    133:     PetscInfo1(ls,"Armijo line search error: alpha (%g) < 1\n", (double)armP->alpha);
    134:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    135:   } else if ((armP->beta <= 0) || (armP->beta >= 1)) {
    136:     PetscInfo1(ls,"Armijo line search error: beta (%g) invalid\n", (double)armP->beta);
    137:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    138:   } else if ((armP->beta_inf <= 0) || (armP->beta_inf >= 1)) {
    139:     PetscInfo1(ls,"Armijo line search error: beta_inf (%g) invalid\n", (double)armP->beta_inf);
    140:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    141:   } else if ((armP->sigma <= 0) || (armP->sigma >= 0.5)) {
    142:     PetscInfo1(ls,"Armijo line search error: sigma (%g) invalid\n", (double)armP->sigma);
    143:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    144:   } else if (armP->memorySize < 1) {
    145:     PetscInfo1(ls,"Armijo line search error: memory_size (%D) < 1\n", armP->memorySize);
    146:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    147:   } else if ((armP->referencePolicy != REFERENCE_MAX) && (armP->referencePolicy != REFERENCE_AVE) && (armP->referencePolicy != REFERENCE_MEAN)) {
    148:     PetscInfo(ls,"Armijo line search error: reference_policy invalid\n");
    149:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    150:   } else if ((armP->replacementPolicy != REPLACE_FIFO) && (armP->replacementPolicy != REPLACE_MRU)) {
    151:     PetscInfo(ls,"Armijo line search error: replacement_policy invalid\n");
    152:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    153:   } else if (PetscIsInfOrNanReal(*f)) {
    154:     PetscInfo(ls,"Armijo line search error: initial function inf or nan\n");
    155:     ls->reason=TAOLINESEARCH_FAILED_BADPARAMETER;
    156:   }

    158:   if (ls->reason != TAOLINESEARCH_CONTINUE_ITERATING) {
    159:     return(0);
    160:   }

    162:   /* Check to see of the memory has been allocated.  If not, allocate
    163:      the historical array and populate it with the initial function
    164:      values. */
    165:   if (!armP->memory) {
    166:     PetscMalloc1(armP->memorySize, &armP->memory );
    167:   }

    169:   if (!armP->memorySetup) {
    170:     for (i = 0; i < armP->memorySize; i++) {
    171:       armP->memory[i] = armP->alpha*(*f);
    172:     }

    174:     armP->current = 0;
    175:     armP->lastReference = armP->memory[0];
    176:     armP->memorySetup=PETSC_TRUE;
    177:   }

    179:   /* Calculate reference value (MAX) */
    180:   ref = armP->memory[0];
    181:   idx = 0;

    183:   for (i = 1; i < armP->memorySize; i++) {
    184:     if (armP->memory[i] > ref) {
    185:       ref = armP->memory[i];
    186:       idx = i;
    187:     }
    188:   }

    190:   if (armP->referencePolicy == REFERENCE_AVE) {
    191:     ref = 0;
    192:     for (i = 0; i < armP->memorySize; i++) {
    193:       ref += armP->memory[i];
    194:     }
    195:     ref = ref / armP->memorySize;
    196:     ref = PetscMax(ref, armP->memory[armP->current]);
    197:   } else if (armP->referencePolicy == REFERENCE_MEAN) {
    198:     ref = PetscMin(ref, 0.5*(armP->lastReference + armP->memory[armP->current]));
    199:   }
    200:   VecDot(g,s,&gdx);

    202:   if (PetscIsInfOrNanReal(gdx)) {
    203:     PetscInfo1(ls,"Initial Line Search step * g is Inf or Nan (%g)\n",(double)gdx);
    204:     ls->reason=TAOLINESEARCH_FAILED_INFORNAN;
    205:     return(0);
    206:   }
    207:   if (gdx >= 0.0) {
    208:     PetscInfo1(ls,"Initial Line Search step is not descent direction (g's=%g)\n",(double)gdx);
    209:     ls->reason = TAOLINESEARCH_FAILED_ASCENT;
    210:     return(0);
    211:   }

    213:   if (armP->nondescending) {
    214:     fact = armP->sigma;
    215:   } else {
    216:     fact = armP->sigma * gdx;
    217:   }
    218:   ls->step = ls->initstep;
    219:   while (ls->step >= ls->stepmin && (ls->nfeval+ls->nfgeval) < ls->max_funcs) {
    220:     /* Calculate iterate */
    221:     VecCopy(x,armP->work);
    222:     VecAXPY(armP->work,ls->step,s);
    223:     if (ls->bounded) {
    224:       VecMedian(ls->lower,armP->work,ls->upper,armP->work);
    225:     }

    227:     /* Calculate function at new iterate */
    228:     if (ls->hasobjective) {
    229:       TaoLineSearchComputeObjective(ls,armP->work,f);
    230:       g_computed=PETSC_FALSE;
    231:     } else if (ls->usegts) {
    232:       TaoLineSearchComputeObjectiveAndGTS(ls,armP->work,f,&gdx);
    233:       g_computed=PETSC_FALSE;
    234:     } else {
    235:       TaoLineSearchComputeObjectiveAndGradient(ls,armP->work,f,g);
    236:       g_computed=PETSC_TRUE;
    237:     }
    238:     if (ls->step == ls->initstep) {
    239:       ls->f_fullstep = *f;
    240:     }

    242:     if (PetscIsInfOrNanReal(*f)) {
    243:       ls->step *= armP->beta_inf;
    244:     } else {
    245:       /* Check descent condition */
    246:       if (armP->nondescending && *f <= ref - ls->step*fact*ref)
    247:         break;
    248:       if (!armP->nondescending && *f <= ref + ls->step*fact) {
    249:         break;
    250:       }

    252:       ls->step *= armP->beta;
    253:     }
    254:   }

    256:   /* Check termination */
    257:   if (PetscIsInfOrNanReal(*f)) {
    258:     PetscInfo(ls, "Function is inf or nan.\n");
    259:     ls->reason = TAOLINESEARCH_FAILED_INFORNAN;
    260:   } else if (ls->step < ls->stepmin) {
    261:     PetscInfo(ls, "Step length is below tolerance.\n");
    262:     ls->reason = TAOLINESEARCH_HALTED_RTOL;
    263:   } else if ((ls->nfeval+ls->nfgeval) >= ls->max_funcs) {
    264:     PetscInfo2(ls, "Number of line search function evals (%D) > maximum allowed (%D)\n",ls->nfeval+ls->nfgeval, ls->max_funcs);
    265:     ls->reason = TAOLINESEARCH_HALTED_MAXFCN;
    266:   }
    267:   if (ls->reason) {
    268:     return(0);
    269:   }

    271:   /* Successful termination, update memory */
    272:   ls->reason = TAOLINESEARCH_SUCCESS;
    273:   armP->lastReference = ref;
    274:   if (armP->replacementPolicy == REPLACE_FIFO) {
    275:     armP->memory[armP->current++] = *f;
    276:     if (armP->current >= armP->memorySize) {
    277:       armP->current = 0;
    278:     }
    279:   } else {
    280:     armP->current = idx;
    281:     armP->memory[idx] = *f;
    282:   }

    284:   /* Update iterate and compute gradient */
    285:   VecCopy(armP->work,x);
    286:   if (!g_computed) {
    287:     TaoLineSearchComputeGradient(ls, x, g);
    288:   }
    289:   PetscInfo2(ls, "%D function evals in line search, step = %g\n",ls->nfeval, (double)ls->step);
    290:   return(0);
    291: }

    295: PETSC_EXTERN PetscErrorCode TaoLineSearchCreate_Armijo(TaoLineSearch ls)
    296: {
    297:   TaoLineSearch_ARMIJO *armP;
    298:   PetscErrorCode       ierr;

    302:   PetscNewLog(ls,&armP);

    304:   armP->memory = NULL;
    305:   armP->alpha = 1.0;
    306:   armP->beta = 0.5;
    307:   armP->beta_inf = 0.5;
    308:   armP->sigma = 1e-4;
    309:   armP->memorySize = 1;
    310:   armP->referencePolicy = REFERENCE_MAX;
    311:   armP->replacementPolicy = REPLACE_MRU;
    312:   armP->nondescending=PETSC_FALSE;
    313:   ls->data = (void*)armP;
    314:   ls->initstep=1.0;
    315:   ls->ops->setup=0;
    316:   ls->ops->apply=TaoLineSearchApply_Armijo;
    317:   ls->ops->view = TaoLineSearchView_Armijo;
    318:   ls->ops->destroy = TaoLineSearchDestroy_Armijo;
    319:   ls->ops->reset = TaoLineSearchReset_Armijo;
    320:   ls->ops->setfromoptions = TaoLineSearchSetFromOptions_Armijo;
    321:   return(0);
    322: }