public Matrix backwardSub(Matrix freeVec) {
		if (this.rows != freeVec.getRows()) {
			throw new IllegalArgumentException("Matrix rows are not aligned!");
		}
		int n = this.rows;

		for (int i = n-1; i >= 0; --i) {
			double value = freeVec.getElement(i, 0) / this.getElement(i, i);
			freeVec.setElement(i, 0, value);
			for (int j = 0; j < i - 1; ++j) {
				value = freeVec.getElement(j, 0) - this.getElement(j, i)
						* freeVec.getElement(i, 0);
				freeVec.setElement(j, 0, value);
			}
		}
		return freeVec;
	}