code: @PublicEvolving
  	public <X extends Value> DeltaIteration<ST, WT> registerAggregationConvergenceCriterion(
  			String name, Aggregator<X> aggregator, ConvergenceCriterion<X> convergenceCheck) {
  		this.aggregators.registerAggregationConvergenceCriterion(name, aggregator, convergenceCheck);
  		return this;
  	}
docs: Registers an {@link Aggregator} for the iteration together with a {@link ConvergenceCriterion}. For a general description
  of aggregators, see {@link #registerAggregator(String, Aggregator)} and {@link Aggregator}.
  At the end of each iteration, the convergence criterion takes the aggregator's global aggregate value and decides whether
  the iteration should terminate. A typical use case is to have an aggregator that sums up the total error of change
  in an iteration step and have to have a convergence criterion that signals termination as soon as the aggregate value
  is below a certain threshold.
  
  @param name The name under which the aggregator is registered.
  @param aggregator The aggregator class.
  @param convergenceCheck The convergence criterion.
  
  @return The DeltaIteration itself, to allow chaining function calls.