That was this symbolic vector operator in which the components are the partial derivative operators.
这个是符号化的向量算子，其中它的分量是偏微分算子。
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.
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。
应用推荐