这个一般读作，而不读作倒三角，或者别的，它是一个算子的符号。
Del so, this guy usually pronounced as del, rather than as pointy triangle going downwards or something like that, it's a symbolic notation for an operator.
此部分为特别作业范例，为一般阅读作业与随堂问题之外之指定作业。
This section contains examples of homework assignments given in addition to the regularly assigned readings and study questions.
应用推荐