CODEWITHSUNDEEP
optimizationopenmdao
tufan
tufan

Reputation: 27

Zero derivative calculation during optimization (no impact to objective)

I am writing an optimization code for a finite-difference radiation solver model. I started to use "src_indices" for connecting parameters rather promoting all the variables. But when I changed the connection, optimization does not calculate derivatives, gives "no impact to objective" error, and successfully terminates optimization after first iteration. Could not find any clue for finding the error in the logs (Bug may be in a completely different reason).

Is there any suggestion where I can start?

I uploaded the code to GitHub https://github.com/TufanAkba/opt_question

Upvotes: 0

Views: 147

Answers (1)

Kenneth Moore
Kenneth Moore

Reputation: 2202

The first thing that comes to mind when you mention "design variables have no impact on objective" is that there may be a missing connection. Since this behavior only started after you changed the connection style, I think this is even more likely.

There are a couple of tools you can use to diagnose this. The first is the n2 viewer, which you can launch by typing the following at your command prompt:

openmdao n2 receiver_opt.py

This will launch a browser window that contains a graphical model viewer which is described in detail here. You can use this to explore the structure of your model. To find unconnected inputs in your model, look for any input blocks that are colored orange. These are technically connected to a hidden IndepVarComp called _auto_ivc, and will include design variables, which are set by the optimizer. You will want to look for any that should be connected to other component outputs.

OpenMDAO also has a connection viewer that just shows connections.

openmdao view_connections receiver_opt.py

You can use this tool to just focus on the connections. It is described here. If you choose to use this, just filter to see any connection to _auto_ivc in the source output string to see the unconnected inputs.

If you reach this point, and are satisfied that all the connections are correct, then there are a couple of other possibilities:

  1. Are all of your src_indices correct? Maybe some of them are an empty set, or maybe some create a "degenerate" case. For example, if you have a set of cascading components that each multiply an incoming vector by a diagonal matrix, and if your indices are [0] in one connection, and [4] in another connection, then you've effectively severed the entire model. None of our visualization tools can pick that up, and you will need to inspect the indices manually.

  2. It could also be a derivative problem, though what you describe sounds like connections. In that case, I recommend using check_partials to look for any missing or incorrect derivatives.

  3. Are you computing any derivatives using complex step? It is possible that you are losing the complex part of the calculation through a complex-unsafe operation. Checking your derivatives against 'fd' can help to find these.

Upvotes: 1

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