6. Adding components to ECF

  1. Adding a genotype

  2. Adding an algorithm

  3. Adding an operator

General rules:


1. Adding a genotype

New genotype classes may be added with 'State::addGenotype(GenotypeP)' function before 'State::initialize', e.g.:

NewGenotypeP gen = (NewGenotypeP) new NewGenotype;

New genotype class must inherit from the abstract Genotype class (see 'Genotype.h'). A genotype should define its own crossover and mutation classes so it can be used in an evolutionary algorithm (see example below). If it does not, it will not change during crossover and mutation of individuals (other genotypes in the individual may change). This might be useful for additional data structures you may want to put in the individual, but don't want them to evolve. Alternatively, you can use the genotype protection option to exclude it from mutation and/or crossover (see the parameters section).

Adding a genotype with the same name as an existing one will replace the original one (if you need to change the genotype's functionality).

An example: a genotype with a vector of double variables (and a pair of operators which do nothing):

// empty crx op
class MyGenotypeCrxOp : public CrossoverOp
	bool mate(GenotypeP gen1, GenotypeP gen2, GenotypeP child)
		// does nothing! (see existing operators)
		return true;
typedef boost::shared_ptr<MyGenotypeCrxOp> MyGenotypeCrxOpP;

// empty mut op
class MyGenotypeMutOp : public MutationOp
	bool mutate(GenotypeP gene)
		// does nothing! (see existing operators)
		return true;
typedef boost::shared_ptr<MyGenotypeMutOp> MyGenotypeMutOpP;

class MyGenotype : public Genotype
	std::vector<double> realValues_;

	// mandatory: define name, other things as needed
		name_ = "MyGenotype";

	// mandatory: must provide copy method
	MyGenotype* copy()
		MyGenotype *newObject = new MyGenotype(*this);
		return newObject;

	// optional: declare crx operators (if not, no crossover will be performed)
	std::vector<CrossoverOpP> getCrossoverOp()
		std::vector<CrossoverOpP> crx;
		crx.push_back(static_cast<CrossoverOpP> (new MyGenotypeCrxOp));
		return crx;

	// optional: declare mut operators (if not, no mutation will be performed)
	std::vector<MutationOpP> getMutationOp()
		std::vector<MutationOpP> mut;
		mut.push_back(static_cast<MutationOpP> (new MyGenotypeMutOp));
		return mut;

	// optional: register any parameters
	void registerParameters(StateP state)
		registerParameter(state, "size", (voidP) (new uint(1)), ECF::UINT);

	// mandatory: build initial genotype structure
	bool initialize(StateP state)
		if(!isParameterDefined(state, "size")) {
			state->getLogger()->log(1, "Error: MyGenotype size not defined");

		voidP sizep = getParameterValue(state, "size");
		uint size = *((uint*) sizep.get());

		// generate random doubles in [0, 1]
		for(uint i = 0; i < size; i++)
			realValues_[i] = state->getRandomizer()->getRandomDouble();

		return true;

	// mandatory: write to XMLNode
	void write(XMLNode &xMyGenotype)
		xMyGenotype = XMLNode::createXMLTopNode("MyGenotype");
		std::stringstream sValue;
		sValue << realValues_.size();
		xMyGenotype.addAttribute("size", sValue.str().c_str());

		for(uint iVar = 0; iVar < realValues_.size(); iVar++)
			sValue << "\t" << realValues_[iVar];

	// read from XMLNode
	// mandatory if running parallel ECF or reading population from a milestone file
	void read(XMLNode& xMyGenotype)
		XMLCSTR values = xMyGenotype.getText();
		std::stringstream sValues;
		sValues << values;

		for(uint iVar = 0; iVar < realValues_.size(); iVar++)
			sValues >> realValues_[iVar];
typedef boost::shared_ptr<MyGenotype> MyGenotypeP;


2. Adding an algorithm

Algoritm must inherit from the abstract Algorithm class (see 'Algorithm.h'). Algorithm may be genotype independent or may define a mandatory genotype structure. It may use genotype's crossover and mutation operators or may define its own (algorithm specific) operators. As an example, see below or e.g. 'AlgSteadyStateTournament.cpp' or 'AlgRouletteWheel.cpp'.

An example: the following algorithm illustrates the basic mechanisms and contains HOW TO code snippets (note that the code is longer than it could be because of optional explanatory parts). The application of a new algorithm is done in 3 steps:

Step 1: First, write an algorithm class:

class MyAlg : public Algorithm

	// declare all available selection operators (not all get used)
	SelFitnessProportionalOpP selFitOp_;
	SelRandomOpP selRandomOp_;
	SelBestOpP selBestOp_;
	SelWorstOpP selWorstOp_;
	// what individual to replace (worst or random)
	bool replaceWorst_;


	// mandatory: define name, construct selection operators
		// the algorithm name will be used in config file (see below)
		name_ = "MyAlg";
		selFitOp_ = (SelFitnessProportionalOpP) (new SelFitnessProportionalOp);
		selRandomOp_ = (SelRandomOpP) (new SelRandomOp);
		selBestOp_ = (SelBestOpP) (new SelBestOp);
		selWorstOp_ = (SelWorstOpP) (new SelWorstOp);

	// optional: register any parameters
	void registerParameters(StateP state)
		// HOW TO: define a parameter
		// string parameter, options: random, worst
		registerParameter(state, "replace", (voidP) (new std::string("random")), ECF::STRING);

	// optional: initialize components, read parameters
	bool initialize(StateP state)
		// selection operators must be initialized if used!
		// optional: set ratio between the best and the worst individual's selection probability
		// if the ratio is < 1, the selection favours worse over better individuals

		// HOW TO: read a parameter value
		// get parameter, decide what to replace
		voidP par = getParameterValue(state, "replace");
		std::string replace = *((std::string*) par.get());
		replaceWorst_ = false;
		if(replace == "worst")
				replaceWorst_ = true;

		// HOW TO: check if genotype is of a specific kind
		// suppose we only accept FloatingPoint
		FloatingPointP flp (new FloatingPoint::FloatingPoint);
		if(state->getGenotypes()[0]->getName() != flp->getName()) {
			ECF_LOG_ERROR(state, "Error: this algorithm accepts only a single FloatingPoint genotype!");
			throw ("");

		// HOW TO: read the dimension and domain boundaries
		voidP sptr = state->getGenotypes()[0]->getParameterValue(state, "dimension");
		uint numDimension = *((uint*) sptr.get());
		voidP lBound = state->getGenotypes()[0]->getParameterValue(state, "lbound");
		double lbound = *((double*) lBound.get());
		voidP uBound = state->getGenotypes()[0]->getParameterValue(state, "ubound");
		double ubound = *((double*) uBound.get());

		// HOW TO: add another genotype in all individuals (if algorithm requires)
		// new FloatingPoint genotype with same parameters
		FloatingPointP fp (static_cast<FloatingPoint::FloatingPoint*> (state->getGenotypes()[0]->copy()));
		fp->setParameterValue(state, "dimension", (voidP) new uint(numDimension));
		fp->setParameterValue(state, "lbound", (voidP) new double(lbound));
		fp->setParameterValue(state, "ubound", (voidP) new double(ubound));

		// HOW TO: read population (local deme) size
		voidP psizep = state->getRegistry()->getEntry("population.size"); 
		uint popSize = *((uint*) psizep.get()); 

		return true;

	// mandatory: perform single 'generation' (however the algorithm defines it)
	bool advanceGeneration(StateP state, DemeP deme)
		// HOW TO: select parents
		IndividualP first = selFitOp_->select(*deme);
		IndividualP second = selBestOp_->select(*deme);

		// select child (random or worst)
		IndividualP child;
				child = selWorstOp_->select(*deme);
				child = selRandomOp_->select(*deme);

		// HOW TO: cross two individuals
		mate(first, second, child);

		// HOW TO: mutate an individual
		// mutation probability defined in Registry!
		// to explicitly mutate an individual:

		// HOW TO: evaluate an individual

		// HOW TO: create a trial individual (e.g. a copy of an existing individual)
		IndividualP trial = (IndividualP) deme->at(0)->copy();

		// HOW TO: access individual data
		// get FloatingPoint genotype from individual
		FloatingPointP fp = boost::static_pointer_cast<FloatingPoint::FloatingPoint> (trial->getGenotype(0));
		// or use ordinary pointers:
		//FloatingPoint::FloatingPoint* fp = static_cast<FloatingPoint::FloatingPoint*> (trial->getGenotype().get());

		// HOW TO: change individual data
		fp->realValue[0] = 3.14;

		// HOW TO: replace an individual in deme
		// evaluate and compare with another individual
			// replace first with second:
			replaceWith(child, trial);

		// some other helper functions (see existing algorithms):
		// copy, replaceWith, removeFrom, isMember

		return true;
typedef boost::shared_ptr<MyAlg> MyAlgP;

Step 2: then, a new algorithm can be added to ECF with 'State::addAlgorithm(AlgorithmP)' function, invoked before 'State::initialize' in your main() function:

NewAlgorithmP alg = (NewAlgorithmP) new NewAlgorithm;

Step 3: finally, the algorithm will only get used if specified in the configuration, e.g.:

                <!-- optional parameter -->
                <Entry key="replace">worst</Entry>


3. Adding an operator

A new general purpose operator may be added with 'State::addOperator(OperatorP)' function:

MyOpP myOp = (MyOpP) new MyOp;

Operator must inherit from the abstract Operator class (see 'Operator.h'). The operator will be used only if its 'initialize' method returns TRUE (which is the default if not reimplemented).
Currently every operator defined in this way is called once each generation (before the generation ends). Further development will allow operators to be called within the algorithm (i.e. before/after mutation, evaluation, crossover)

An example: the following operator simply stops the evolution if the generation number is specified in the configuration file (e.g. with <Entry key="my.stopgen">10</Entry>):

class MyOp : public Operator
	uint myStopGen_;

	// optional: register any parameters
	void registerParameters(StateP state)
		state->getRegistry()->registerEntry("my.stopgen", (voidP) (new uint(0)), ECF::UINT);

	// optional: initialize (with parameter check)
	bool initialize(StateP state)
		// if parameter not defined in config, return false (inactive operator)
			return false;
		// otherwise, read param. value and return true (active operator)
		voidP sptr = state->getRegistry()->getEntry("my.stopgen");
		myStopGen_ = *((uint*) sptr.get());
		return true;

	// mandatory: actual operation
	bool operate(StateP state)
		// read generation no, stop if needed
		if(state->getGenerationNo() == myStopGen_)
		return true;
typedef boost::shared_ptr<MyOp> MyOpP;

TODO: setInitMethod, addMutationOp, addCrossoverOp, addTerminationOp