cm2435 / diffusion-limited-aggregation

Repo to version simulation for Ising and DLA models in C++

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diffusion-limited-aggregation's Issues

Double Checks of stick probability

When performing stick calculations you perform two probabilistic checks for a successful stick. This can be seen in the following two code sections:

diffusion-limited-aggregation/src/DLASystem.cpp

Lines 208 to 220 in bafd073

	if (checkStick()) {
	//cout << "stick" << endl;
	if(rgen.random01() < StickProb){
	setParticleInactive(); // make the particle inactive (stuck)
	updateClusterRadius(lastP->pos); // update the cluster radius, addCircle, etc.
	if (numParticles % 100 == 0 && logfile.is_open()) {
	logfile << numParticles << " " << clusterRadius << endl;
	}
	bool verb = false;
	string LogRow = LogRadius(verb);
	LogfileRows.push_back(LogRow);
	}
	}

diffusion-limited-aggregation/src/DLASystem.cpp

Lines 233 to 252 in bafd073

	int DLASystem::checkStick(double StickProb) {
	//Stickprob should not be able to be greater than one, it is a probability
	if (StickProb > 1.0){
	throw std::invalid_argument( "StickProb was set greater than one" );
	};
	Particle *lastP = particleList[numParticles - 1];
	int result = 0;
	// loop over neighbours
	for (int i = 0; i < 4; i++) {
	double checkpos[2];
	setPosNeighbour(checkpos, lastP->pos, i);
	// if the neighbour is occupied...
	if (readGrid(checkpos) == 1){
	if (rgen.random01() < StickProb){
	result = 1;
	}
	};
	}
	return result;
	}

Both approaches are valid, either inserting the probability check after we have confirmed we are in the correct location (the first code block), or for each possible stick (up, down, left, right). However the inclusion of both is an error giving you a stick probability $p_{err} \sim p^2$.

We should ask the lecturers which behaviour is correct, I chose the former but thinking about it the latter may be more "correct".