[docs] update autodiff tutorial

docs/Project.toml

@@ -3,6 +3,7 @@ CDDLib = "3391f64e-dcde-5f30-b752-e11513730f60"
 CSV = "336ed68f-0bac-5ca0-87d4-7b16caf5d00b"
 Clarabel = "61c947e1-3e6d-4ee4-985a-eec8c727bd6e"
 DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
+DifferentiationInterface = "a0c0ee7d-e4b9-4e03-894e-1c5f64a51d63"
 DimensionalData = "0703355e-b756-11e9-17c0-8b28908087d0"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
@@ -43,12 +44,13 @@ CDDLib = "=0.9.4"
 CSV = "0.10"
 Clarabel = "=0.9.0"
 DataFrames = "1"
+DifferentiationInterface = "0.6.5"
 DimensionalData = "0.27.3"
 Distributions = "0.25"
 Documenter = "=1.6.0"
 DocumenterCitations = "1"
 Dualization = "0.5"
-Enzyme = "0.12.14"
+Enzyme = "0.13.7"
 ForwardDiff = "0.10"
 GLPK = "=1.2.1"
 HTTP = "1.5.4"

docs/src/tutorials/nonlinear/operator_ad.jl

@@ -35,6 +35,7 @@
 
 using JuMP
 import Enzyme
+import DifferentiationInterface
 import ForwardDiff
 import Ipopt
 import Test
@@ -248,18 +249,18 @@ Test.@test ≈(analytic_g, enzyme_g)
 # differentiation.
 
 # The code to implement the Hessian in Enzyme is complicated, so we will not
-# explain it in detail; see the [Enzyme documentation](https://enzymead.github.io/Enzyme.jl/v0.11.20/generated/autodiff/#Vector-forward-over-reverse).
+# explain it in detail; see the [Enzyme documentation](https://enzymead.github.io/Enzyme.jl/stable/generated/autodiff/#Vector-forward-over-reverse).
 
 function enzyme_∇²f(H::AbstractMatrix{T}, x::Vararg{T,N}) where {T,N}
     ## direction(i) returns a tuple with a `1` in the `i`'th entry and `0`
     ## otherwise
     direction(i) = ntuple(j -> Enzyme.Active(T(i == j)), N)
     ## As the inner function, compute the gradient using Reverse mode
-    ∇f_deferred(x...) = Enzyme.autodiff_deferred(Enzyme.Reverse, f, x...)[1]
+    ∇f(x...) = Enzyme.autodiff(Enzyme.Reverse, f, Enzyme.Active, x...)[1]
     ## For the outer autodiff, use Forward mode.
     hess = Enzyme.autodiff(
         Enzyme.Forward,
-        ∇f_deferred,
+        ∇f,
         ## Compute multiple evaluations of Forward mode, each time using `x` but
         ## initializing with a different direction.
         Enzyme.BatchDuplicated.(Enzyme.Active.(x), ntuple(direction, N))...,
@@ -296,10 +297,10 @@ function enzyme_derivatives(f::Function)
     end
     function ∇²f(H::AbstractMatrix{T}, x::Vararg{T,N}) where {T,N}
         direction(i) = ntuple(j -> Enzyme.Active(T(i == j)), N)
-        ∇f_deferred(x...) = Enzyme.autodiff_deferred(Enzyme.Reverse, f, x...)[1]
+        ∇f(x...) = Enzyme.autodiff(Enzyme.Reverse, f, Enzyme.Active, x...)[1]
         hess = Enzyme.autodiff(
             Enzyme.Forward,
-            ∇f_deferred,
+            ∇f,
             Enzyme.BatchDuplicated.(Enzyme.Active.(x), ntuple(direction, N))...,
         )[1]
         for j in 1:N, i in 1:j
@@ -324,3 +325,105 @@ function enzyme_rosenbrock()
 end
 
 enzyme_rosenbrock()
+
+# ## DifferentiationInterface
+
+# Julia offers [many different autodiff packages](https://juliadiff.org/).
+# [DifferentiationInterface.jl](https://github.com/gdalle/DifferentiationInterface.jl)
+# is a package that provides an abstraction layer across multiple underlying
+# autodiff libaries.
+
+# All the necessary information about your choice of underlyingg autodiff
+# package is encoded in a "backend object" like this one:
+
+DifferentiationInterface.AutoForwardDiff()
+
+# This type comes from another package called [ADTypes.jl](https://github.com/SciML/ADTypes.jl),
+# but DifferentiationInterface re-exports it. Other options include
+# `AutoZygote()` and `AutoFiniteDiff()`.
+
+# ### Gradient
+
+# Apart from providing the backend object, the syntax below remains very
+# similar:
+
+function di_∇f(
+    g::AbstractVector{T},
+    x::Vararg{T,N};
+    backend = DifferentiationInterface.AutoForwardDiff(),
+) where {T,N}
+    DifferentiationInterface.gradient!(splat(f), g, backend, collect(x))
+    return
+end
+
+# Let's check that we find the analytic solution:
+
+di_g = zeros(2)
+di_∇f(di_g, x...)
+Test.@test ≈(analytic_g, di_g)
+
+# ### Hessian
+
+# The Hessian follows exactly the same logic, except we need only the lower
+# triangle.
+
+function di_∇²f(
+    H::AbstractMatrix{T},
+    x::Vararg{T,N};
+    backend = DifferentiationInterface.AutoForwardDiff(),
+) where {T,N}
+    H_dense = DifferentiationInterface.hessian(splat(f), backend, collect(x))
+    for i in 1:N, j in 1:i
+        H[i, j] = H_dense[i, j]
+    end
+    return
+end
+
+# Let's check that we find the analytic solution:
+
+di_H = zeros(2, 2)
+di_∇²f(di_H, x...)
+Test.@test ≈(analytic_H, di_H)
+
+# ### JuMP example
+
+# The code for computing the gradient and Hessian using DifferentiationInterface
+# can be re-used for many operators. Thus, it is helpful to encapsulate it into
+# the function:
+
+"""
+    di_derivatives(f::Function; backend) -> Tuple{Function,Function}
+
+Return a tuple of functions that evaluate the gradient and Hessian of `f` using
+DifferentiationInterface.jl with any given `backend`.
+"""
+function di_derivatives(f::Function; backend)
+    function ∇f(g::AbstractVector{T}, x::Vararg{T,N}) where {T,N}
+        DifferentiationInterface.gradient!(splat(f), g, backend, collect(x))
+        return
+    end
+    function ∇²f(H::AbstractMatrix{T}, x::Vararg{T,N}) where {T,N}
+        H_dense =
+            DifferentiationInterface.hessian(splat(f), backend, collect(x))
+        for i in 1:N, j in 1:i
+            H[i, j] = H_dense[i, j]
+        end
+        return
+    end
+    return ∇f, ∇²f
+end
+
+# Here's an example using `di_derivatives`:
+
+function di_rosenbrock(; backend)
+    model = Model(Ipopt.Optimizer)
+    set_silent(model)
+    @variable(model, x[1:2])
+    @operator(model, op_rosenbrock, 2, f, di_derivatives(f; backend)...)
+    @objective(model, Min, op_rosenbrock(x[1], x[2]))
+    optimize!(model)
+    Test.@test is_solved_and_feasible(model)
+    return value.(x)
+end
+
+di_rosenbrock(; backend = DifferentiationInterface.AutoForwardDiff())