When using the Demux block to extract and output elements from a vector input, you can use -1 in a vector expression to indicate that the block dynamically sizes the corresponding port. When a vector expression comprises both positive values and -1 values, the block assigns as many elements as needed to the ports with positive values. The block distributes the remaining elements as evenly as possible over the ports with -1 values.
In this example, the Number of outputs parameter of the Demux block is set to [-1, 3, -1]. Thus, the block outputs three signals where the second signal always has three elements. The sizes of the first and third signals depend on the size of the input signal. For an input vector with seven elements, the Demux block outputs two elements on the first port, three elements on the second port, and two elements on the third port.