Add Duplicated methods (#192)

* add Duplicated methods

* add test

* test for shared params + minimal docs

* remove 1.6 CI

* indent by two spaces

* fix doctest

Author: mcabbott

.github/workflows/ci.yml

@@ -15,9 +15,9 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1.6'
           - '1'
           - 'nightly'
+          - "1.10"
         os:
           - ubuntu-latest
         arch:

Project.toml

@@ -1,26 +1,34 @@
 name = "Optimisers"
 uuid = "3bd65402-5787-11e9-1adc-39752487f4e2"
+version = "0.4.1"
 authors = ["Mike J Innes <[email protected]>"]
-version = "0.4.0"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
+EnzymeCore = "f151be2c-9106-41f4-ab19-57ee4f262869"
 Functors = "d9f16b24-f501-4c13-a1f2-28368ffc5196"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
+[weakdeps]
+EnzymeCore = "f151be2c-9106-41f4-ab19-57ee4f262869"
+
+[extensions]
+OptimisersEnzymeCoreExt = "EnzymeCore"
+
 [compat]
 ChainRulesCore = "1"
+EnzymeCore = "0.8.5"
 Functors = "0.4.9, 0.5"
 Statistics = "1"
 Zygote = "0.6.40"
-julia = "1.6"
+julia = "1.10"
 
 [extras]
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 
 [targets]
-test = ["Test", "StaticArrays", "Zygote"]
+test = ["Test", "EnzymeCore", "StaticArrays", "Zygote"]

docs/src/index.md

@@ -358,3 +358,12 @@ julia> Optimisers.update!(opt_state, x, g);
 julia> opt_state # the state in `a` and `b` differ
 (a = Leaf(Adam(0.1, (0.9, 0.999), 1.0e-8), ([0.09, 0.09], [0.000999, 0.000999], (0.729, 0.997003))), b = Leaf(Adam(0.1, (0.9, 0.999), 1.0e-8), ([0.1, 0.1], [0.001, 0.001], (0.81, 0.998001))))
 ```
+
+## Usage with [Enzyme.jl](https://github.com/EnzymeAD/Enzyme.jl)
+
+Enzyme.jl is a new automatic differentiation package, an alternative to Zygote.jl.
+It likes to store the model and the gradient together, as an object `Duplicated(x, dx)`.
+
+Optimisers.jl now has some methods to handle this:
+* `update!(opt_state, Duplicated(model, grad))` uses the gradient to update both the model and the optimiser state, and
+* `setup(::AbstractRule, ::Duplicated)` ignores the gradient and returns `setup(rule, model)`.

ext/OptimisersEnzymeCoreExt.jl

@@ -0,0 +1,60 @@
+module OptimisersEnzymeCoreExt
+
+import Optimisers: trainable, setup, update!, isnumeric, AbstractRule, _setup
+import EnzymeCore: Duplicated, Const
+
+using Functors: fmapstructure
+
+trainable(x::Duplicated) = (; val = x.val)
+trainable(x::Const) = (;)
+
+"""
+    setup(rule::AbstractRule, model_grad::Duplicated)
+
+For use with Enzyme's Duplicated, this just calls `setup(rule, model_grad.val)`.
+"""
+setup(rule::AbstractRule, model_grad::Duplicated) = setup(rule, model_grad.val)
+
+_setup(rule, x::Duplicated; cache) = throw(ArgumentError(
+  """Objects of type `Duplicated` are only supported by Optimisers.jl at top level,
+  they may not appear deep inside other objects."""
+))
+
+"""
+    update!(opt_state, model_grad::Duplicated)
+
+For use with Enzyme's `Duplicated`, which holds both a model/parameters
+and the corresponding gradient.
+
+# Example
+
+```jldoctest
+julia> using Optimisers, EnzymeCore
+
+julia> x_dx = Duplicated(Float16[1,2,3], Float16[1,0,-4])
+Duplicated{Vector{Float16}}(Float16[1.0, 2.0, 3.0], Float16[1.0, 0.0, -4.0])
+
+julia> st = Optimisers.setup(Momentum(1/9), x_dx)  # acts only on x not on dx
+Leaf(Momentum(0.111111, 0.9), Float16[0.0, 0.0, 0.0])
+
+julia> Optimisers.update!(st, x_dx)  # mutates both arguments
+
+julia> x_dx
+Duplicated{Vector{Float16}}(Float16[0.8887, 2.0, 3.445], Float16[1.0, 0.0, -4.0])
+
+julia> st
+Leaf(Momentum(0.111111, 0.9), Float16[0.1111, 0.0, -0.4443])
+```
+"""
+function update!(opt_state, model_grad::Duplicated)
+  _, _ = update!(opt_state, model_grad.val, _grad_or_nothing(model_grad))
+  nothing
+end
+
+# This function strips the returned gradient to be Zygote-like,
+# most importantly prune=nothing removes 2nd appearance of shared gradient to avoid double-counting.
+_grad_or_nothing(dup::Duplicated) = fmapstructure(_grad_or_nothing, dup.dval; prune=nothing)
+_grad_or_nothing(::Const) = nothing
+_grad_or_nothing(x) = isnumeric(x) ? x : nothing
+
+end

test/runtests.jl

@@ -1,5 +1,5 @@
 using Optimisers
-using ChainRulesCore, Functors, StaticArrays, Zygote
+using ChainRulesCore, Functors, StaticArrays, Zygote, EnzymeCore
 using LinearAlgebra, Statistics, Test, Random
 using Optimisers: @.., @lazy
 using Base.Broadcast: broadcasted, instantiate, Broadcasted
@@ -534,6 +534,28 @@ end
         @test Optimisers._norm(bc2, p) isa Float64
       end
     end
+
+    @testset "Enzyme Duplicated" begin
+      x_dx = Duplicated(Float16[1,2,3], Float16[1,0,-4])
+      st = Optimisers.setup(Momentum(1/9), x_dx)  # acts only on x not on dx
+      @test st isa Optimisers.Leaf
+      @test nothing === Optimisers.update!(st, x_dx)  # mutates both arguments
+      @test x_dx.val ≈ Float16[0.8887, 2.0, 3.445]
+
+      shared = [1.0]
+      model = (x=shared, y=shared)
+      grad = deepcopy(model) # Enzyme produces something like this, grad.x === grad.y, already accumulated.
+      dup = Duplicated(model, model)
+      st2 = Optimisers.setup(Descent(0.1), model)
+      Optimisers.update!(st2, dup)
+      @test model.x ≈ [0.9]
+      shared .= 1
+      Optimisers.update!(st2, model, grad)
+      model.x ≈ [0.8]  # This is wrong, but don't make it a test.
+      # Ideally, perhaps the 3-arg update! could notice that grad.x===grad.y, and not accumulate the gradient in this case?
+
+      @test_throws ArgumentError Optimisers.setup(Adam(), (; a=[1,2,3.], b=x_dx))  # Duplicated deep inside is not allowed
+    end
   end
   @testset verbose=true "Destructure" begin
     include("destructure.jl")