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Improve rules for sum #336

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Merged
merged 7 commits into from
May 7, 2021
Merged

Improve rules for sum #336

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f3f43b4
tweaks to sum rules
Dec 26, 2020
7d2050c
Apply suggestions from code review
mcabbott May 6, 2021
8b95848
comma
mcabbott May 6, 2021
2b882c1
v0.7.62
mcabbott May 7, 2021
eab273b
Merge branch 'master' into sum2
mcabbott May 7, 2021
082c73c
gone cold one more time...
mcabbott May 7, 2021
c5402c6
Merge branch 'master' into sum2
mcabbott May 7, 2021
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2 changes: 1 addition & 1 deletion Project.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
name = "ChainRules"
uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
version = "0.7.62"
version = "0.7.63"

[deps]
ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
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17 changes: 12 additions & 5 deletions src/rulesets/Base/mapreduce.jl
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Expand Up @@ -10,9 +10,10 @@ function rrule(::typeof(sum), x::AbstractArray{T}; dims=:) where {T<:Number}
y = sum(x; dims=dims)
function sum_pullback(ȳ)
# broadcasting the two works out the size no-matter `dims`
x̄ = broadcast(x, ȳ) do xi, ȳi
ȳi
end
x̄ = InplaceableThunk(
@thunk(broadcast(last∘tuple, x, ȳ)),
x -> x .+= ȳ
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@oxinabox oxinabox May 7, 2021

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This reminded me we to do JuliaDiff/ChainRulesCore.jl#348
but i think even once that is merged this is still better (also that will not always work if dims are different, which maybe should change JuliaDiff/ChainRulesCore.jl#349)

)
return (NO_FIELDS, x̄)
end
return y, sum_pullback
Expand All @@ -29,7 +30,9 @@ function frule(
∂y = if dims isa Colon
2 * real(dot(x, ẋ))
elseif VERSION ≥ v"1.2" # multi-iterator mapreduce introduced in v1.2
2 * mapreduce(_realconjtimes, +, x, ẋ; dims=dims)
mapreduce(+, x, ẋ; dims=dims) do xi, dxi
2 * _realconjtimes(xi, dxi)
end
else
2 * sum(_realconjtimes.(x, ẋ); dims=dims)
end
Expand All @@ -44,7 +47,11 @@ function rrule(
) where {T<:Union{Real,Complex}}
y = sum(abs2, x; dims=dims)
function sum_abs2_pullback(ȳ)
return (NO_FIELDS, DoesNotExist(), 2 .* real.(ȳ) .* x)
x_thunk = InplaceableThunk(
@thunk(2 .* real.(ȳ) .* x),
dx -> dx .+= 2 .* real.(ȳ) .* x
)
return (NO_FIELDS, DoesNotExist(), x_thunk)
end
return y, sum_abs2_pullback
end