efficient set的用法和樣例：
例句
- By using active set strategy, the authors need only to solve a reduced trust region subproblem which is solved inexactly by the truncated conjugate gradient method.
作者利用有效集策略，在每次迭代中只需求解一個(gè)低維的信賴(lài)域子問(wèn)題，該信賴(lài)域子問(wèn)題是通過(guò)截斷共軛梯度法來(lái)近似求解的。
