AlgEvolutionStrategy.cpp

#include "ECF_base.h"
#include "ECF_macro.h"
#include "AlgEvolutionStrategy.h"
#include "SelBestOp.h"
#include "SelRandomOp.h"
#include <algorithm>
 
 
EvolutionStrategy::EvolutionStrategy()
{
    // define algorithm name
    name_ = "EvolutionStrategy";
 
    // create selection operators needed
    selBestOp_ = static_cast<SelectionOperatorP> (new SelBestOp);
    selRandomOp_ = static_cast<SelectionOperatorP> (new SelRandomOp);
}
 
 
void EvolutionStrategy::registerParameters(StateP state)
{
    registerParameter(state, "lambda", (voidP) new uint(4), ECF::UINT, 
        "number of offspring created in each iteration (default: 4)");
    registerParameter(state, "rho", (voidP) new uint(1), ECF::UINT, 
        "number of parents used to create an offspring; may be 1 or 2 (default: 1)");
    registerParameter(state, "mu", (voidP) new uint(1), ECF::UINT, 
        "the size of parent population (default: 1)");
    registerParameter(state, "selection", (voidP) new std::string("plus"), ECF::STRING, 
        "selection scheme: \"plus\", uses both parents and offspring) or \"comma\", uses just offspring (default: plus)");
}
 
 
bool EvolutionStrategy::initialize(StateP state)
{
    // initialize all operators
    selBestOp_->initialize(state);
    selRandomOp_->initialize(state);
 
    // read parameter values
    voidP sizep = getParameterValue(state, "lambda");
    lambda_ = *((uint*) sizep.get());
 
    voidP rhop = getParameterValue(state, "rho");
    rho_ = *((uint*) rhop.get());
 
    if(rho_ < 1 || rho_ > 2) {
        ECF_LOG_ERROR(state, "Error: number of parents to create an offspring in EvolutionStrategy can only be 1 or 2!");
        throw "";
    }
 
    voidP mup = getParameterValue(state, "mu");
    mu_ = *((uint*) mup.get());
 
    if(mu_ < rho_) {
        ECF_LOG_ERROR(state, "Error: size of parent population in EvolutionStrategy must be greater than number of parents to create an offspring!");
        throw "";
    }
 
 
    voidP sptr = state->getRegistry()->getEntry("population.size");
    uint demeSize = *((uint*) sptr.get());
    if(demeSize % mu_ != 0 || mu_ < 1) {
        ECF_LOG_ERROR(state, "Error: \"population.size\" parameter must be a multiple of size of parent population (mu) in EvolutionStrategy algorithm!");
        throw "";
    }
 
    voidP selp = getParameterValue(state, "selection");
    std::string sels = *((std::string*) selp.get());
    if(sels == "plus")
        plusSelection_ = true;
    else if(sels == "comma")
        plusSelection_ = false;
    else {
        ECF_LOG_ERROR(state, "Error: selection type in EvolutionStrategy can only be \"plus\" or \"comma\"!");
        throw "";
    }
 
    if(plusSelection_ == false && lambda_ <= mu_) {
        ECF_LOG_ERROR(state, "Error: offspring number (lambda) in comma EvolutionStrategy must be greater than the number of parents (mu)!");
        throw "";
    }
 
    return true;
}
 
 
bool EvolutionStrategy::advanceGeneration(StateP state, DemeP deme)
{
    subPopulations_ = (uint) deme->size() / mu_;
 
    // repeat the same ES for each parent subpopulation
    for(uint subPopulation = 0; subPopulation < subPopulations_; subPopulation++) {
 
        // use appropriate portion of the deme
        uint firstInd = subPopulation * mu_;
        uint lastInd = (subPopulation + 1) * mu_;
 
        // construct parent pool
        std::vector<IndividualP> parents;
        for(uint ind = firstInd; ind < lastInd; ind++)
            parents.push_back(deme->at(ind));
 
        // create offspring pool
        std::vector<IndividualP> offspring;
        for(uint iChild = 0; iChild < lambda_; iChild++) {
            // randomly select rho parents, create one child
            IndividualP child;
            // use mutation
            if(rho_ == 1) {
                IndividualP parent = selRandomOp_->select(parents);
                child = copy(parent);
                mutation_->mutate(child);
            }
            // use crossover
            else if(rho_ == 2) {
                IndividualP p1 = selRandomOp_->select(parents);
                IndividualP p2 = p1;
                while(p1 == p2)
                    p2 = selRandomOp_->select(parents);
                child = copy(p1);
                mate(p1, p2, child);
            }
            offspring.push_back(child);
            // evaluate offspring
            evaluate(child);
        }
 
        // construct selection pool for new generation parents
        std::vector<IndividualP> selPool;
        if(plusSelection_) {
            // arrange selection pool from both best parents and offspring
            selPool = parents;
            selPool.insert(selPool.end(), offspring.begin(), offspring.end());
        }
        else
            // select from offspring only
            selPool = offspring;
 
        // sort by fitness (best first)
        std::sort(selPool.begin(), selPool.end(), &EvolutionStrategy::compare);
 
        // replace new generation in deme
        uint selected = 0;
        for(uint ind = firstInd; ind < lastInd; ind++, selected++)
            replaceWith(ind, selPool[selected]);
    }
 
    return true;
}