code: public double calcKMeansCosts(double[] center, ClusteringFeature points) {
  		assert (this.sumPoints.length == center.length &&
  				this.sumPoints.length == points.sumPoints.length);
  		return (this.sumSquaredLength + points.sumSquaredLength)
  				- 2 * Metric.dotProductWithAddition(this.sumPoints,
  						points.sumPoints, center)
  				+ (this.numPoints + points.numPoints)
  				* Metric.dotProduct(center);
  	}
docs: Calculates the k-means costs of the ClusteringFeature and another
  ClusteringFeature too a center.
  
  @param center
  the center too calculate the costs
  @param points
  the points too calculate the costs
  @return the costs