private static Tensor multiplyWithFactory(Sum sum, Tensor factor, Transformation... transformations) { final ArrayList<Tensor> newSumData = new ArrayList<>(sum.size()); Tensor temp; boolean reduced = false; for (int i = sum.size() - 1; i >= 0; --i) { temp = Transformation.Util.applySequentially(multiply(factor, sum.get(i)), transformations); if (!TensorUtils.isZero(temp)) { newSumData.add(temp); if (!reduced && isReduced(sum.get(i), factor, temp)) reduced = true; } } if (newSumData.size() == 0) return Complex.ZERO; if (newSumData.size() == 1) return newSumData.get(0); final Tensor[] data = newSumData.toArray(new Tensor[newSumData.size()]); if (reduced) return SumFactory.FACTORY.create(data); return new Sum(data, IndicesFactory.create(newSumData.get(0).getIndices().getFree())); }