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I dispute the sentence "Other shorthands include a subscripted t as in x_t." While subscript notation can be used to refer to derivatives, I've never seen it used for a time derivative. The reason is that the notation x_t is discrete-time notation for the level (not change) of x at time t.

Unless someone objects, I will delete this sentence. Please respond pro or con. Duoduoduo (talk) 19:46, 4 July 2010 (UTC)[reply]