title: Modeling a linear system with Python
body: <p>I would like to simulate/model a closed-loop, linear, time-invariant system (specifically a locked PLL approximation) with python. </p>
  
  <p>Each sub-block within the model has a known transfer function which is given in terms of complex frequency <code>H(s) = K / ( s * tau + 1 )</code>.  Using the model, I would like to see how the system response as well as the noise response is affected as parameters (e.g. the VCO gain) are changed.  This would involve using Bode plots and root-locus plots.  </p>
  
  <p>What Python modules should I seek out to get the job done?  </p>