I'll go ahead and merge, assuming that tests pass and correctness is unaffected.

There is still one instance of zeroTangentVector that is being used in the codebase at

SwiftFusion/Sources/SwiftFusion/Core/LieGroup.swift

Line 170 in 9eca609

return pullback(at: v.zeroTangentVector, in: { self.Adjoint($0) })(v)

that I've had some trouble replacing, but I'll work on it as well. All other uses in the codebase are not being used as Richard Wei mentioned in his issue.

Thanks for mentioning this. @acoadmarmon: do you have ideas and time to fix this remaining zeroTangentVector usage?

I think it should be possible by adding some conformance requirement on LieGroupCoordinate.LocalCoordinate (protocol requirement inherited from ManifoldCoordinate.LocalCoordinate) to a new protocol like DifferentiableHasInstanceZeroTangentVector (not great name) that refines Differentiable with an additional requirement var zeroTangentVector: TangentVector.

Pinging others in case they have time and see a better solution: @marcrasi @dabrahams @rxwei

@dan-zheng I can work on this but it will take a few days given my current to-do list and the added complexity of changing zeroTangentVector for this object. Since this seems to be a blocker for another issue, if anyone has time to fix this in the shorter term I'd defer to them. I'll pick this back up on Sunday if it hasn't been solved by then.

Thanks for the quick update Andrew! Unless anyone (@rxwei) has higher urgency, I think fixing the remaining zeroTangentVector usage whenever you have time sounds great.