code: @Override
  	public double getVariance() {
  		if(isDeterministic()) {
  			return 0.0;
  		}
  		if(size() == 0) {
  			return Double.NaN;
  		}
  
  		double sum			= 0.0;
  		double sumOfSquared = 0.0;
  		for (double realization : getRealizations()) {
  			sum += realization;
  			sumOfSquared += realization * realization;
  		}
  		return sumOfSquared/size() - sum/size() * sum/size();
  	}
docs: /* (non-Javadoc)
  @see net.finmath.stochastic.RandomVariable#getVariance()