是求偏导的常用表示符号，其读法参考wiki，可以如下：
The symbol is variously referred to as "curly d", "rounded d", "curved d", "dabba", or "Jacobi's delta",[6] or as "del"[7] (but this name is also used for the "nabla" symbol ∇).
It may also be pronounced simply "dee",[8] "partial dee",[9][10] "doh",[11][12] or "die".[13]