JuliaDiff / JuliaDiff/ForwardDiff.jl
StackOverflowError with complex `sqrt`
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Description
When differentiating over a complex sqrt
x0 = 5
ForwardDiff.derivative(x -> sqrt(1im * x), x0)
a StackOverflowError is encountered.
StackOverflowError:
Stacktrace:
[1] sqrt(::Complex{ForwardDiff.Dual{ForwardDiff.Tag{##20#21,Int64},Float16,1}}) at ./complex.jl:416 (repeats 80000 times)
The stacktrace points to the following declaration
sqrt(z::Complex) = sqrt(float(z))
I have found similar issues #111 #196 #239, but I don't see how I can fix this problem.
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the reproducer in the issue and inspect the sqrt(::Complex) declaration at complex.jl:416. Compare the behavior with related issues #111, #196, and #239. Done means the complex sqrt differentiation case no longer recurses into a StackOverflowError.
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Assessment
- Tech stack
- julia
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 32/100