docs: 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);
  	}