Lines transmit signals in the direction indicated by the arrow. Lines must always transmit signals from the output terminal of one block to the input terminal of another block. One exception to this is that a line can tap off of another line. This sends the original signal to two (or more) destination blocks.
Lines can never inject a signal into another line; lines must be combined through the use of block such as a summing junction. A signal can be either a scalar signal or a vector signal.
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