public void addMember(Instance instance) {
		if (numOfMembers == 0) {
			featureVector = new FeatureVector();
			for (Entry<Integer, Double> entry : instance.getFeatureVector().getVector().entrySet()) {
				featureVector.add(entry.getKey(), entry.getValue());
			}			
			numOfMembers = 1;
		}
		else {
			this.featureVector.scalarDivide(1.0/numOfMembers);
			this.featureVector.add(instance);
			numOfMembers ++;
			this.featureVector.scalarDivide(numOfMembers);
		}
	}