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。
2
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。
3
In most clinical symptoms of periodical occurred problems can be viewed as a double bound supplements symbolic enrichment, namely symptom is a negative operator limit supplements enrichment.