public Array2D add(Array2D ary) {
		if (attIndex1 != ary.attIndex1 || attIndex2 != ary.attIndex2) {
			throw new IllegalArgumentException("Cannot add arrays on differnt terms");
		}
		for (int i = 0; i < predictions.length; i++) {
			double[] preds1 = predictions[i];
			double[] preds2 = ary.predictions[i];
			for (int j = 0; j < preds1.length; j++) {
				preds1[j] += preds2[j];
			}
		}
		return this;
	}