a constrained smile的用法和样例：
- He said it with a constrained smile.
- "Nay," said the King, with a constrained smile, "that last remark upon the shaving utensils, Oliver, is too much in the style of thine own peculiar occupation to be combated by any one.
- a constrained smile; forced heartiness; a strained smile.
- He told us the sad news in a constrained voice.
- Genetic algorithm is a constrained stochastic optimization method.