setSIMode中small attacker mode（cap|current|zero_mearn）怎么理解

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-accumulated_small_attacker_mode {cap | current | zero_mean}
Specifies whether to use the current-matching based method for accumulated small attackers.
cap: Uses the accumulated small attacker method, which matches the total coupling capacitance of an attacker with the small attackers that are being virtualized. This is the default mode for all process nodes above 45nm.
current: Uses the current-matching based method for accumulated small attackers. With this method,the transitions on virtual attackers are modeled using Piece Wise Linear (PWL) waveforms. The PWL waveforms are generated in a way that the current induced by the transition matches the total current induced by all accumulated small attacker components.
zero_mean: A new accumulation method where series of small attackers, that is, attackers less than the individual attacker threshold value, are assumed to transition in opposing directions and thus cancel one another in aggregate.
Default: current - for 45nm and below process nodes.


cap | current | zero_mean这三种算法怎么理解