It condenses three things into one line: initial condition, increment, and ending condition.
它将三件事浓缩成一行：初始条件、增量和结束条件。
2
If not NULL, increment the line counter.
如果不是NULL，则增加行计数器。
3
When grounding fault happens at the time when current is zero, the transient value is too small, in order to prevent it, the paper brings forward the current increment method to select faulty line.