DCGain:

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   Computes the DC gain of a discrete time state space system.

   Since version 1.
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   Form:
   g = DCGain( a, b, c, d, sType )
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   Inputs
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   a                   Discrete plant matrix
   b                   Discrete input matrix
   c                   Discrete output matrix
   d                   Discrete feedthrough matrix
   sType               State equation type ('Delta' or 'Z')

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   Outputs
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   g                   Gain

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