The smaller the value of the merit function is, the closer the iteration point is to the solution. 当价值函数的值越小时，迭代点越靠近最优解。
Furthermore, the model will keep iterating within the feasible region whenever the iterative point is feasible, and become feasible decreasing directions method. 进一步地，一旦迭代点进入可行域，模型就能保持在可行域内迭代，成为可行下降类算法。
