OpenMDAO: finite difference flag for Component.solve_nonlinear

Question

For some of our components it would be useful to know whether it's being executed as part of a finite difference calculation or not. One example could be a meshing component where we'd want to maintain the same node count and distribution function during FD and allow for remeshing during major iteration steps. In the old OpenMDAO we could detect this from a component's itername. Would it be possible to reintroduce this or is that info already available to the Component class?

Answer 1

I can't think of any current way to figure out if you are inside an FD when solve_nonlinear is being called, but it's a good idea for the reasons that you mention.

Answer 2

We don't currently have that capability, but others have also asked to be informed when solve_nonlinear is being run for complex step as well.

One way to do this would be to introduce an optional_argument to solve_nonlinear such as call_mode="fd" or call_mode="cs" or call_mode="solve". The only problem with this approach is that its very backwards incompatible.

Another approach would be to add a regular python attribute to the component that you could check like self.call_mode="solve", etc. This one would be a pretty easy change and I think it would serve the purpose.

One last possible way would be to put a flag into the unknowns/params vector. So you would check params.call_mode to see what mode. This is somewhat sensible since its the param values that change when you're going to complex-step.

I think I like the last option the best. Both solve_nonlinear and apply_nonlinear need to know about this information. But none of the other methods do. So making it a component attribute seems a little out of place.