Gradient definitions & supertypes for Zygote, continued #169
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mcabbott
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Sep 30, 2021
mcabbott
reviewed
Sep 30, 2021
src/zygote.jl
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| # Define a new species of projection operator for this type: | ||
| ChainRulesCore.ProjectTo(x::VectorOfArray) = ChainRulesCore.ProjectTo{VectorOfArray}() | ||
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| # Gradient from iteration will be e.g. Vector{Vector}, this makes it another AbstractMatrix | ||
| (::ChainRulesCore.ProjectTo{VectorOfArray})(dx::AbstractVector{<:AbstractArray}) = VectorOfArray(dx) | ||
| # Gradient from broadcasting will be another AbstractArray | ||
| (::ChainRulesCore.ProjectTo{VectorOfArray})(dx::AbstractArray) = dx |
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I believe this may not be necessary at all. One thing I thought to test was whether iteration like this worked without it, but it does, it hits the @adjoint getindex rule:
julia> function iter(vofa)
s = 0
for a in vofa
s += prod(a)
end
s
end;
julia> gradient(iter, va)[1]
VectorOfArray{Float64,3}:
2-element Vector{Matrix{Float64}}:
[0.007377548303139424 0.0014293014720444096 0.0004998127128840348; 0.0005414269337139141 0.0007721441834498009 0.0006559506948612249; 0.0042378737935180105 0.0006765914005991947 0.00045986425172967415]
[0.002774992305796606 0.002978041675310144 0.004412709924140469; 0.0056425205408066285 0.005228088118453952 0.0036646150274027; 0.0036825199036535465 0.004902176341789764 0.045170987413739046]
mcabbott
reviewed
Sep 30, 2021
src/zygote.jl
Outdated
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| # These rules duplicate the `rrule` methods above, because Zygote looks for an `@adjoint` | ||
| # definition first, and finds its own before finding those. | ||
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| ZygoteRules.@adjoint function getindex(VA::AbstractVectorOfArray, i::Union{Int,AbstractArray{Int},CartesianIndex,Colon,BitArray,AbstractArray{Bool}}) | ||
| function AbstractVectorOfArray_getindex_adjoint(Δ) | ||
| Δ′ = [ (i == j ? Δ : zero(x)) for (x,j) in zip(VA.u, 1:length(VA))] |
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Unrelated to the PR, but this seems like it allocates quite a bit, when iterating a VectorOfArray. I guess that using Fill(0.0, size(Δ)) would often make Δ′ have an abstract type?
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Yes, it would make it an abstract type and sometimes hurt inference. Then we'd have to rely on union optimizations and pray.
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Relying on union optimizations might be the right idea here though, I'll have to check.
Co-authored-by: Michael Abbott <[email protected]>
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Continues #168
@mcabbott
I didn't have the write permissions for some reason so continuing it here.