關于cst里面導出的powerflow 有沒有人知道他具體是怎么得來的

如題！
她說 This monitor stores the Poynting vector of the electromagnetic field.
The monitor represents the maximum value (peak value) of the power flow at every spatial point, encountered within one period of time. Therefore, this type of monitor is time independent。
到底是怎么回事啊 請高手指點一下，謝謝

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是不是EXH?