LyapG:

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   Solve the general Lyapunov equation ap + pa' + q = 0

   Since version 1.
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   Form: 
   [p, err] = LyapG( a, q )
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   Inputs
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   a                   Matrix
   q                   Matrix

   -------
   Outputs
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   p                   Solution
   err                 Norm of the error

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