title: Are partial derivatives ever calculated in reverse mode?
body: <p>I understand that openMDAO can compute the total derivatives of a model in forward or reverse mode, but are partial derivatives always calculated in forward mode?</p>
  
  <p>For example, I have a component with 400 inputs and 4 outputs. Obviously, this is a candidate for a reverse-mode solve. If I just <code>declare_partials(['*'], ['*'], method=fd)</code>, will openMDAO ever attempt to solve this in reverse mode?</p>