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[WIP] Add Zygote repeat rrules #405

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rayegun wants to merge 15 commits into from
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[WIP] Add Zygote repeat rrules #405

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b4e5ae8
Add repeat rrules
Apr 30, 2021
0778cd3
No kwargs sensitivities (don't DoesNotExist)
Apr 30, 2021
779b8a3
Tests, fix kwargs(?)
Apr 30, 2021
e97e3c6
Use fkwargs
Apr 30, 2021
d4ba658
Version bump
Apr 30, 2021
a3c4f13
Update src/rulesets/Base/array.jl
Apr 30, 2021
e1e2843
Update src/rulesets/Base/array.jl
Apr 30, 2021
db385a6
Update src/rulesets/Base/array.jl
Apr 30, 2021
f9f1548
Update src/rulesets/Base/array.jl
Apr 30, 2021
bdb1eb9
Update src/rulesets/Base/array.jl
Apr 30, 2021
15b758a
add frules and rule for zero-dim
Apr 30, 2021
09c8f2e
1 error on fill(4.0) rrule
Apr 30, 2021
c4d38ee
Formatting
Apr 30, 2021
f55670d
More formatting
Apr 30, 2021
eabd344
Rm frules
Apr 30, 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 = "0.7.61"
version = "0.7.62"

[deps]
ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
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37 changes: 37 additions & 0 deletions src/rulesets/Base/array.jl
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Expand Up @@ -103,3 +103,40 @@ function rrule(::typeof(fill), value::Any, dims::Int...)
end
return fill(value, dims), fill_pullback
end

#####
##### `repeat`
#####

function rrule(::typeof(repeat), x::AbstractVector, m::Integer)
function repeat_pullback(Ȳ)
return (NO_FIELDS, dropdims(sum(reshape(Ȳ, length(x), :); dims=2); dims=2), DoesNotExist())
Comment on lines +112 to +113
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@nickrobinson251 nickrobinson251 May 1, 2021

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should this close over length(x) rather than x (to reduce memory requirements)?

Suggested change
function repeat_pullback(Ȳ)
return (NO_FIELDS, dropdims(sum(reshape(Ȳ, length(x), :); dims=2); dims=2), DoesNotExist())
length_x = length(x)
function repeat_pullback(Ȳ)
return (NO_FIELDS, dropdims(sum(reshape(Ȳ, length_x, :); dims=2); dims=2), DoesNotExist())

And likewise with the size calls in the rules below.

This is a genuine question, i'm not sure what best practice here is (cc @oxinabox).

I believe this would be manually doing one thing we want an OpaqueClosure to be able to do automatically.
Also maybe this should be mentioned on the "writing good rules docs"?

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@oxinabox oxinabox May 2, 2021

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Yeah, I am cautious about doing that since it makes code uglier.
So I wouldn't block a PR over it (it can always be optimized later)
But it does save memory.
We should discuss this with pros and cons in "Writing God Rules"

end
return repeat(x, m), repeat_pullback
end

function rrule(::typeof(repeat), x::AbstractVecOrMat, m::Integer, n::Integer=1)
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@mcabbott mcabbott Apr 30, 2021

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Since things like repeat(rand(Int8,2,2,2),1,1,2,2) are allowed, it might be nice to treat the general case? Untested, but my attempt is:

function rrule(::typeof(repeat), x::AbstractArray, scales::Integer...)
    function repeat_pullback_1(dy)
        size2ndims = ntuple(d -> isodd(d) ? size(x,1+d÷2) : get(scales,d÷2,1), 2*ndims(dy))
        sumdy = sum(reshape(dy, size2ndims); dims = ntuple(d -> 2d, ndims(dy)))
        return (NO_FIELDS, reshape(sumdy, size(x)), map(_->DoesNotExist(), scales)...)
    end
    return repeat(x, scales...), repeat_pullback_1
end

What this won't handle is repeat(1:2, 3,2,1,0) but perhaps nobody will write that!

function repeat_pullback(Ȳ)
Ȳ′ = reshape(Ȳ, size(x, 1), m, size(x, 2), n)
return (NO_FIELDS, reshape(sum(Ȳ′; dims=(2,4)), size(x)), DoesNotExist(), DoesNotExist())
end
return repeat(x, m, n), repeat_pullback
end

function rrule(::typeof(repeat), xs::AbstractArray; inner=ntuple(_->1, ndims(xs)), outer=ntuple(_->1, ndims(xs)))
function repeat_pullback(Ȳ)
Ȳ′ = zero(xs)
S = size(xs)
for (dest_idx, val) ∈ pairs(IndexCartesian(), Ȳ)
src_idx = [mod1(div(dest_idx[dim] - 1, inner[dim]) + 1, S[dim]) for dim ∈ 1:length(S)]
Ȳ′[src_idx...] += val
end
return (NO_FIELDS, Ȳ′)
end
return repeat(xs; inner=inner, outer=outer), repeat_pullback
end

function rrule(::typeof(repeat), x::AbstractArray{<:Real, 0}, m::Integer)
repeat_pullback(Ȳ) = (NO_FIELDS, similar(x, eltype(Ȳ)) .= sum(Ȳ), DoesNotExist())
return repeat(x, m), repeat_pullback
end
10 changes: 10 additions & 0 deletions test/rulesets/Base/array.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -35,3 +35,13 @@ end
test_rrule(fill, 44.0, 4; check_inferred=false)
test_rrule(fill, 2.0, (3, 3, 3) ⊢ DoesNotExist())
end

@testset "repeat" begin
test_rrule(repeat, randn(5), 3)
test_rrule(repeat, randn(5), 3, 3)
test_rrule(repeat, randn(3, 3), 2)
test_rrule(repeat, randn(5, 5), 2,5)
test_rrule(repeat, randn(5, 4, 3); fkwargs=(inner=(2, 2, 1), outer=(1, 1, 3)))
test_rrule(repeat, fill(4.0), 3)

end