structuredPlaner_tpl.h

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/****************************************************************************
 *   This file is part of the aGrUM/pyAgrum library.                        *
 *                                                                          *
 *   Copyright (c) 2005-2026 by                                             *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
 *                                                                          *
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 *   SPDX-FileCopyrightText: Copyright 2005-2026                            *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
 *   SPDX-License-Identifier: LGPL-3.0-or-later OR MIT                      *
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 ****************************************************************************/
 
#pragma once
 

 
// =========================================================================
#include <queue>
#include <vector>
// #include <algorithm>
// #include <utility>
//  =========================================================================
#include <agrum/base/core/functors.h>
 
#include <agrum/base/core/math/math_utils.h>
// =========================================================================
#include <agrum/base/multidim/implementations/multiDimFunctionGraph.h>
#include <agrum/base/multidim/instantiation.h>
#include <agrum/base/multidim/tensor.h>
// =========================================================================
#include <agrum/FMDP/planning/structuredPlaner.h>
// =========================================================================

#define RECAST(x) reinterpret_cast< const MultiDimFunctionGraph< GUM_ELEMENT >* >(x)
 
namespace gum {
 
 
  /* **************************************************************************************************
   * **/
  /* ** **/
  /* **                                Constructors / Destructors **/
  /* ** **/
  /* **************************************************************************************************
   * **/
 
  // ===========================================================================
  // Default constructor
  // ===========================================================================
  template < typename GUM_ELEMENT >
  StructuredPlaner< GUM_ELEMENT >::StructuredPlaner(IOperatorStrategy< GUM_ELEMENT >* opi,
                                                    GUM_ELEMENT discountFactor,
                                                    GUM_ELEMENT epsilon,
                                                    bool        verbose) :
      discountFactor_(discountFactor), operator_(opi), verbose_(verbose) {
    GUM_CONSTRUCTOR(StructuredPlaner);
 
    _threshold_    = epsilon;
    vFunction_     = nullptr;
    optimalPolicy_ = nullptr;
  }
 
  // ===========================================================================
  // Default destructor
  // ===========================================================================
  template < typename GUM_ELEMENT >
  StructuredPlaner< GUM_ELEMENT >::~StructuredPlaner() {
    GUM_DESTRUCTOR(StructuredPlaner);
 
    if (vFunction_) { delete vFunction_; }
 
    if (optimalPolicy_) delete optimalPolicy_;
 
    delete operator_;
  }
 
  /* **************************************************************************************************
   * **/
  /* ** **/
  /* **                                Datastructure access methods **/
  /* ** **/
  /* **************************************************************************************************
   * **/
 
  // ===========================================================================
  // Initializes data structure needed for making the planning
  // ===========================================================================
  template < typename GUM_ELEMENT >
  std::string StructuredPlaner< GUM_ELEMENT >::optimalPolicy2String() {
    // ************************************************************************
    // Discarding the case where no \pi* have been computed
    if (!optimalPolicy_ || optimalPolicy_->root() == 0) return "NO OPTIMAL POLICY CALCULATED YET";
 
    // ************************************************************************
    // Initialisation
 
    // Declaration of the needed string stream
    std::string output;
    std::string terminalStream;
    std::string nonTerminalStream;
    std::string arcstream;
 
    // First line for the toDot
    output += "\ndigraph \" OPTIMAL POLICY \" {\n";
 
    // Form line for the internal node stream en the terminal node stream
    terminalStream += "node [shape = box];\n";
    nonTerminalStream += "node [shape = ellipse];\n";
 
    // For somme clarity in the final string
    std::string tab = "\t";
 
    // To know if we already checked a node or not
    Set< NodeId > visited;
 
    // FIFO of nodes to visit
    std::queue< NodeId > fifo;
 
    // Loading the FIFO
    fifo.push(optimalPolicy_->root());
    visited << optimalPolicy_->root();
 
 
    // ************************************************************************
    // Main loop
    while (!fifo.empty()) {
      // Node to visit
      NodeId currentNodeId = fifo.front();
      fifo.pop();
 
      // Checking if it is terminal
      if (optimalPolicy_->isTerminalNode(currentNodeId)) {
        // Get back the associated ActionSet
        ActionSet ase = optimalPolicy_->nodeValue(currentNodeId);
 
        // Creating a line for this node
        terminalStream += std::format("{0}{1};{0}{1} [label=\"{1} - ", tab, currentNodeId);
 
        // Enumerating and adding to the line the associated optimal actions
        for (SequenceIteratorSafe< Idx > valIter = ase.beginSafe(); valIter != ase.endSafe();
             ++valIter) {
          terminalStream += fmdp_->actionName(*valIter);
          terminalStream += ' ';
        }
 
        // Terminating line
        terminalStream += "\"];\n";
        continue;
      }
 
      // Either wise
      {
        // Geting back the associated internal node
        const InternalNode* currentNode = optimalPolicy_->node(currentNodeId);
 
        // Creating a line in internalnode stream for this node
        nonTerminalStream += std::format("{0}{1};{0}{1} [label=\"{1} - {2}\"];\n",
                                         tab,
                                         currentNodeId,
                                         currentNode->nodeVar()->name());
 
        // Going through the sons and agregating them according the the sons Ids
        HashTable< NodeId, LinkedList< Idx >* > sonMap;
        for (Idx sonIter = 0; sonIter < currentNode->nbSons(); ++sonIter) {
          if (!visited.exists(currentNode->son(sonIter))) {
            fifo.push(currentNode->son(sonIter));
            visited << currentNode->son(sonIter);
          }
          if (!sonMap.exists(currentNode->son(sonIter)))
            sonMap.insert(currentNode->son(sonIter), new LinkedList< Idx >());
          sonMap[currentNode->son(sonIter)]->addLink(sonIter);
        }
 
        // Adding to the arc stram
        for (auto sonIter = sonMap.beginSafe(); sonIter != sonMap.endSafe(); ++sonIter) {
          arcstream += std::format("{}{} -> {} [label=\" ", tab, currentNodeId, sonIter.key());
          Link< Idx >* modaIter = sonIter.val()->list();
          while (modaIter) {
            arcstream += currentNode->nodeVar()->label(modaIter->element());
            if (modaIter->nextLink()) arcstream += ", ";
            modaIter = modaIter->nextLink();
          }
          arcstream += "\",color=\"#00ff00\"];\n";
          delete sonIter.val();
        }
      }
    }
 
    // Terminating
    output += terminalStream + '\n' + nonTerminalStream + '\n' + arcstream + "\n}\n";
 
    return output;
  }
 
  /* **************************************************************************************************
   * **/
  /* ** **/
  /* **                                     Planning Methods **/
  /* ** **/
  /* **************************************************************************************************
   * **/
 
  // ===========================================================================
  // Initializes data structure needed for making the planning
  // ===========================================================================
  template < typename GUM_ELEMENT >
  void StructuredPlaner< GUM_ELEMENT >::initialize(const FMDP< GUM_ELEMENT >* fmdp) {
    fmdp_ = fmdp;
 
    // Determination of the threshold value
    _threshold_ *= (1 - discountFactor_) / (2 * discountFactor_);
 
    // Establishement of sequence of variable elemination
    for (auto varIter = fmdp_->beginVariables(); varIter != fmdp_->endVariables(); ++varIter)
      elVarSeq_ << fmdp_->main2prime(*varIter);
 
    // Initialisation of the value function
    vFunction_     = operator_->getFunctionInstance();
    optimalPolicy_ = operator_->getAggregatorInstance();
    _firstTime_    = true;
  }
 
  // ===========================================================================
  // Performs a value iteration
  // ===========================================================================
  template < typename GUM_ELEMENT >
  void StructuredPlaner< GUM_ELEMENT >::makePlanning(Idx nbStep) {
    if (_firstTime_) {
      this->initVFunction_();
      _firstTime_ = false;
    }
 
    // *****************************************************************************************
    // Main loop
    // *****************************************************************************************
    Idx         nbIte = 0;
    GUM_ELEMENT gap   = _threshold_ + 1;
    while ((gap > _threshold_) && (nbIte < nbStep)) {
      ++nbIte;
 
      MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = this->valueIteration_();
 
      // *****************************************************************************************
      // Then we compare new value function and the old one
      MultiDimFunctionGraph< GUM_ELEMENT >* deltaV = operator_->subtract(newVFunction, vFunction_);
      gap                                          = 0;
 
      for (deltaV->beginValues(); deltaV->hasValue(); deltaV->nextValue())
        if (gap < fabs(deltaV->value())) gap = fabs(deltaV->value());
      delete deltaV;
 
      if (verbose_)
        std::cout << " ------------------- Fin itération n° " << nbIte << std::endl
                  << " Gap : " << gap << " - " << _threshold_ << std::endl;
 
      // *****************************************************************************************
      // And eventually we update pointers for next loop
      delete vFunction_;
      vFunction_ = newVFunction;
    }
 
    // *****************************************************************************************
    // Policy matching value function research
    // *****************************************************************************************
    this->evalPolicy_();
  }
 
  // ===========================================================================
  // Performs a single step of value iteration
  // ===========================================================================
  template < typename GUM_ELEMENT >
  void StructuredPlaner< GUM_ELEMENT >::initVFunction_() {
    vFunction_->copy(*(RECAST(fmdp_->reward())));
  }
 
  /* **************************************************************************************************
   * **/
  /* ** **/
  /* **                                   Value Iteration Methods **/
  /* ** **/
  /* **************************************************************************************************
   * **/
 
 
  // ===========================================================================
  // Performs a single step of value iteration
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::valueIteration_() {
    // *****************************************************************************************
    // Loop reset
    MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = operator_->getFunctionInstance();
    newVFunction->copyAndReassign(*vFunction_, fmdp_->mapMainPrime());
 
    // *****************************************************************************************
    // For each action
    std::vector< MultiDimFunctionGraph< GUM_ELEMENT >* > qActionsSet;
    for (auto actionIter = fmdp_->beginActions(); actionIter != fmdp_->endActions(); ++actionIter) {
      MultiDimFunctionGraph< GUM_ELEMENT >* qAction = this->evalQaction_(newVFunction, *actionIter);
      qActionsSet.push_back(qAction);
    }
    delete newVFunction;
 
    // *****************************************************************************************
    // Next to evaluate main value function, we take maximise over all action
    // value, ...
    newVFunction = this->maximiseQactions_(qActionsSet);
 
    // *******************************************************************************************
    // Next, we eval the new function value
    newVFunction = this->addReward_(newVFunction);
 
    return newVFunction;
  }
 
  // ===========================================================================
  // Evals the q function for current fmdp action
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::evalQaction_(
      const MultiDimFunctionGraph< GUM_ELEMENT >* Vold,
      Idx                                         actionId) {
    // ******************************************************************************
    // Initialisation :
    // Creating a copy of last Vfunction to deduce from the new Qaction
    // And finding the first var to eleminate (the one at the end)
 
    return operator_->regress(Vold, actionId, this->fmdp_, this->elVarSeq_);
  }
 
  // ===========================================================================
  // Maximise the AAction to iobtain the vFunction
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::maximiseQactions_(
      std::vector< MultiDimFunctionGraph< GUM_ELEMENT >* >& qActionsSet) {
    MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = qActionsSet.back();
    qActionsSet.pop_back();
 
    while (!qActionsSet.empty()) {
      MultiDimFunctionGraph< GUM_ELEMENT >* qAction = qActionsSet.back();
      qActionsSet.pop_back();
      newVFunction = operator_->maximize(newVFunction, qAction);
    }
 
    return newVFunction;
  }
 
  // ===========================================================================
  // Maximise the AAction to iobtain the vFunction
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::minimiseFunctions_(
      std::vector< MultiDimFunctionGraph< GUM_ELEMENT >* >& qActionsSet) {
    MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = qActionsSet.back();
    qActionsSet.pop_back();
 
    while (!qActionsSet.empty()) {
      MultiDimFunctionGraph< GUM_ELEMENT >* qAction = qActionsSet.back();
      qActionsSet.pop_back();
      newVFunction = operator_->minimize(newVFunction, qAction);
    }
 
    return newVFunction;
  }
 
  // ===========================================================================
  // Updates the value function by multiplying by discount and adding reward
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< GUM_ELEMENT >*
      StructuredPlaner< GUM_ELEMENT >::addReward_(MultiDimFunctionGraph< GUM_ELEMENT >* Vold,
                                                  Idx                                   actionId) {
    // *****************************************************************************************
    // ... we multiply the result by the discount factor, ...
    MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = operator_->getFunctionInstance();
    newVFunction->copyAndMultiplyByScalar(*Vold, this->discountFactor_);
    delete Vold;
 
    // *****************************************************************************************
    // ... and finally add reward
    newVFunction = operator_->add(newVFunction, RECAST(fmdp_->reward(actionId)));
 
    return newVFunction;
  }
 
  /* **************************************************************************************************
   * **/
  /* ** **/
  /* **                                   Optimal Policy Evaluation Methods **/
  /* ** **/
  /* **************************************************************************************************
   * **/
 
  // ===========================================================================
  // Evals the policy corresponding to the given value function
  // ===========================================================================
  template < typename GUM_ELEMENT >
  void StructuredPlaner< GUM_ELEMENT >::evalPolicy_() {
    // *****************************************************************************************
    // Loop reset
    MultiDimFunctionGraph< GUM_ELEMENT >* newVFunction = operator_->getFunctionInstance();
    newVFunction->copyAndReassign(*vFunction_, fmdp_->mapMainPrime());
 
    std::vector< MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* >
        argMaxQActionsSet;
    // *****************************************************************************************
    // For each action
    for (auto actionIter = fmdp_->beginActions(); actionIter != fmdp_->endActions(); ++actionIter) {
      MultiDimFunctionGraph< GUM_ELEMENT >* qAction = this->evalQaction_(newVFunction, *actionIter);
 
      qAction = this->addReward_(qAction);
 
      argMaxQActionsSet.push_back(makeArgMax_(qAction, *actionIter));
    }
    delete newVFunction;
 
 
    // *****************************************************************************************
    // Next to evaluate main value function, we take maximise over all action
    // value, ...
    MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* argMaxVFunction
        = argmaximiseQactions_(argMaxQActionsSet);
 
    // *****************************************************************************************
    // Next to evaluate main value function, we take maximise over all action
    // value, ...
    extractOptimalPolicy_(argMaxVFunction);
  }
 
  // ===========================================================================
  // Creates a copy of given in parameter decision Graph and replaces leaves
  // of that Graph by a pair containing value of the leaf and action to which
  // is bind this Graph (given in parameter).
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >*
      StructuredPlaner< GUM_ELEMENT >::makeArgMax_(
          const MultiDimFunctionGraph< GUM_ELEMENT >* qAction,
          Idx                                         actionId) {
    MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* amcpy
        = operator_->getArgMaxFunctionInstance();
 
    // Insertion des nouvelles variables
    for (SequenceIteratorSafe< const DiscreteVariable* > varIter
         = qAction->variablesSequence().beginSafe();
         varIter != qAction->variablesSequence().endSafe();
         ++varIter)
      amcpy->add(**varIter);
 
    HashTable< NodeId, NodeId > src2dest;
    amcpy->manager()->setRootNode(
        _recurArgMaxCopy_(qAction->root(), actionId, qAction, amcpy, src2dest));
 
    delete qAction;
    return amcpy;
  }
 
  // ==========================================================================
  // Recursion part for the createArgMaxCopy
  // ==========================================================================
  template < typename GUM_ELEMENT >
  NodeId StructuredPlaner< GUM_ELEMENT >::_recurArgMaxCopy_(
      NodeId                                                                         currentNodeId,
      Idx                                                                            actionId,
      const MultiDimFunctionGraph< GUM_ELEMENT >*                                    src,
      MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* argMaxCpy,
      HashTable< NodeId, NodeId >&                                                   visitedNodes) {
    if (visitedNodes.exists(currentNodeId)) return visitedNodes[currentNodeId];
 
    NodeId nody;
    if (src->isTerminalNode(currentNodeId)) {
      ArgMaxSet< GUM_ELEMENT, Idx > leaf(src->nodeValue(currentNodeId), actionId);
      nody = argMaxCpy->manager()->addTerminalNode(leaf);
    } else {
      const InternalNode* currentNode = src->node(currentNodeId);
      NodeId*             sonsMap     = static_cast< NodeId* >(
          SOA_ALLOCATE(sizeof(NodeId) * currentNode->nodeVar()->domainSize()));
      for (Idx moda = 0; moda < currentNode->nodeVar()->domainSize(); ++moda)
        sonsMap[moda]
            = _recurArgMaxCopy_(currentNode->son(moda), actionId, src, argMaxCpy, visitedNodes);
      nody = argMaxCpy->manager()->addInternalNode(currentNode->nodeVar(), sonsMap);
    }
    visitedNodes.insert(currentNodeId, nody);
    return nody;
  }
 
  // ===========================================================================
  // Performs argmax_a Q(s,a)
  // ===========================================================================
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >*
      StructuredPlaner< GUM_ELEMENT >::argmaximiseQactions_(
          std::vector< MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >,
                                              SetTerminalNodePolicy >* >& qActionsSet) {
    MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* newVFunction
        = qActionsSet.back();
    qActionsSet.pop_back();
 
    while (!qActionsSet.empty()) {
      MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >* qAction
          = qActionsSet.back();
      qActionsSet.pop_back();
      newVFunction = operator_->argmaximize(newVFunction, qAction);
    }
 
    return newVFunction;
  }
 
  // ===========================================================================
  // Creates a copy of given in parameter decision Graph and replaces leaves
  // of that Graph by a pair containing value of the leaf and action to which
  // is bind this Graph (given in parameter).
  // ===========================================================================
  template < typename GUM_ELEMENT >
  void StructuredPlaner< GUM_ELEMENT >::extractOptimalPolicy_(
      const MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >*
          argMaxOptimalValueFunction) {
    optimalPolicy_->clear();
 
    // Insertion des nouvelles variables
    for (SequenceIteratorSafe< const DiscreteVariable* > varIter
         = argMaxOptimalValueFunction->variablesSequence().beginSafe();
         varIter != argMaxOptimalValueFunction->variablesSequence().endSafe();
         ++varIter)
      optimalPolicy_->add(**varIter);
 
    HashTable< NodeId, NodeId > src2dest;
    optimalPolicy_->manager()->setRootNode(_recurExtractOptPol_(argMaxOptimalValueFunction->root(),
                                                                argMaxOptimalValueFunction,
                                                                src2dest));
 
    delete argMaxOptimalValueFunction;
  }
 
  // ==========================================================================
  // Recursion part for the createArgMaxCopy
  // ==========================================================================
  template < typename GUM_ELEMENT >
  NodeId StructuredPlaner< GUM_ELEMENT >::_recurExtractOptPol_(
      NodeId currentNodeId,
      const MultiDimFunctionGraph< ArgMaxSet< GUM_ELEMENT, Idx >, SetTerminalNodePolicy >*
                                   argMaxOptVFunc,
      HashTable< NodeId, NodeId >& visitedNodes) {
    if (visitedNodes.exists(currentNodeId)) return visitedNodes[currentNodeId];
 
    NodeId nody;
    if (argMaxOptVFunc->isTerminalNode(currentNodeId)) {
      ActionSet leaf;
      _transferActionIds_(argMaxOptVFunc->nodeValue(currentNodeId), leaf);
      nody = optimalPolicy_->manager()->addTerminalNode(leaf);
    } else {
      const InternalNode* currentNode = argMaxOptVFunc->node(currentNodeId);
      NodeId*             sonsMap     = static_cast< NodeId* >(
          SOA_ALLOCATE(sizeof(NodeId) * currentNode->nodeVar()->domainSize()));
      for (Idx moda = 0; moda < currentNode->nodeVar()->domainSize(); ++moda)
        sonsMap[moda] = _recurExtractOptPol_(currentNode->son(moda), argMaxOptVFunc, visitedNodes);
      nody = optimalPolicy_->manager()->addInternalNode(currentNode->nodeVar(), sonsMap);
    }
    visitedNodes.insert(currentNodeId, nody);
    return nody;
  }
 
  // ==========================================================================
  // Extract from an ArgMaxSet the associated ActionSet
  // ==========================================================================
  template < typename GUM_ELEMENT >
  void
      StructuredPlaner< GUM_ELEMENT >::_transferActionIds_(const ArgMaxSet< GUM_ELEMENT, Idx >& src,
                                                           ActionSet& dest) {
    for (auto idi = src.beginSafe(); idi != src.endSafe(); ++idi)
      dest += *idi;
  }
 
  template < typename GUM_ELEMENT >
  StructuredPlaner< GUM_ELEMENT >*
      StructuredPlaner< GUM_ELEMENT >::spumddInstance(GUM_ELEMENT discountFactor,
                                                      GUM_ELEMENT epsilon,
                                                      bool        verbose) {
    return new StructuredPlaner< GUM_ELEMENT >(new MDDOperatorStrategy< GUM_ELEMENT >(),
                                               discountFactor,
                                               epsilon,
                                               verbose);
  }
 
  template < typename GUM_ELEMENT >
  StructuredPlaner< GUM_ELEMENT >*
      StructuredPlaner< GUM_ELEMENT >::sviInstance(GUM_ELEMENT discountFactor,
                                                   GUM_ELEMENT epsilon,
                                                   bool        verbose) {
    return new StructuredPlaner< GUM_ELEMENT >(new TreeOperatorStrategy< GUM_ELEMENT >(),
                                               discountFactor,
                                               epsilon,
                                               verbose);
  }
 
  template < typename GUM_ELEMENT >
  const FMDP< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::fmdp() {
    return fmdp_;
  }
 
  template < typename GUM_ELEMENT >
  const MultiDimFunctionGraph< GUM_ELEMENT >* StructuredPlaner< GUM_ELEMENT >::vFunction() {
    return vFunction_;
  }
 
  template < typename GUM_ELEMENT >
  Size StructuredPlaner< GUM_ELEMENT >::vFunctionSize() {
    return vFunction_ != nullptr ? vFunction_->realSize() : 0;
  }
 
  template < typename GUM_ELEMENT >
  MultiDimFunctionGraph< ActionSet, SetTerminalNodePolicy >*
      StructuredPlaner< GUM_ELEMENT >::optimalPolicy() {
    return optimalPolicy_;
  }
 
  template < typename GUM_ELEMENT >
  Size StructuredPlaner< GUM_ELEMENT >::optimalPolicySize() {
    return optimalPolicy_ != nullptr ? optimalPolicy_->realSize() : 0;
  }
 
}   // end of namespace gum