Unexpected zero derivative

[swilliamson7]

Not sure if this is an Enzyme issue or a my code issue, but Enzyme is returning a zero where I would expect a non-zero value. I'm using Checkpointing + Enzyme to try and compute a derivative of a cost function w.r.t. a specific parameter, and running this script will attempt to do it. It successfully runs, the relevant variables in the output structures S and dS are S.parameters.J (this is the total value of the cost function), and dS.parameters.\gamma\_0 (this is the derivative I want). I did a finite difference calculation to find the derivative and I really think it shouldn't be zero, so I'm not quite sure what's happening.

Happy to provide more info if needed!

[swilliamson7]

An update to this, I think the zero is happening because the initial derivative is being chosen incorrectly/something is happening with the initial derivative. This could fall under either Enzyme or Checkpointing, I'm not sure which is causing it, but I get a correct non-zero value if I modify my code slightly so it's not quite a full issue

[wsmoses]

@swilliamson7 I assume this is resolved by our debug session earlier? Please reopen if not