diff --git a/Project.toml b/Project.toml
index 08a0793..a09b3a8 100644
--- a/Project.toml
+++ b/Project.toml
@@ -6,6 +6,7 @@ version = "0.0.1"
 
 [deps]
 Catlab = "134e5e36-593f-5add-ad60-77f754baafbe"
+ComponentArrays = "b0b7db55-cfe3-40fc-9ded-d10e2dbeff66"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 NLsolve = "2774e3e8-f4cf-5e23-947b-6d7e65073b56"
@@ -13,6 +14,7 @@ Optim = "429524aa-4258-5aef-a3af-852621145aeb"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Reexport = "189a3867-3050-52da-a836-e630ba90ab69"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
+StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 StatsBase = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
@@ -21,7 +23,7 @@ Catlab = "0.16.10"
 ForwardDiff = "0.10.36"
 NLsolve = "4.5.1"
 Optim = "1.9.4"
+Reexport = "1.2.2"
 SparseArrays = "1.10.0"
 StatsBase = "0.34.3"
 julia = "1.10"
-Reexport = "1.2.2"
diff --git a/docs/literate/literate_example.jl b/docs/literate/literate_example.jl
index 941b4c6..a3654f5 100644
--- a/docs/literate/literate_example.jl
+++ b/docs/literate/literate_example.jl
@@ -10,4 +10,4 @@ using AlgebraicOptimization
 #
 # We provide the `hello(string)` method which prints "Hello, `string`!"
 
-#hello("World")
+# hello("World")
diff --git a/src/FinSetAlgebras.jl b/src/FinSetAlgebras.jl
index bf87137..20d3651 100644
--- a/src/FinSetAlgebras.jl
+++ b/src/FinSetAlgebras.jl
@@ -2,7 +2,7 @@
 # TODO: upstream into Catlab.jl
 module FinSetAlgebras
 
-export FinSetAlgebra, CospanAlgebra, Open, hom_map, laxator, data, portmap
+export FinSetAlgebra, CospanAlgebra, Open, hom_map, laxator, data, portmap, draw, draw_types
 
 using LinearAlgebra, SparseArrays
 using Catlab
@@ -82,9 +82,13 @@ end
 data(obj::Open{T}) where T = obj.o
 portmap(obj::Open{T}) where T = obj.m
 
-# Helper function for when m is identity.
+# Helper functions for when m is identity.
 function Open{T}(o::T) where T
-    Open{T}(domain(o), o, id(domain(o)))
+    Open{T}(dom(o), o, id(dom(o)))
+end
+
+function Open{T}(S::FinSet, o::T) where T
+    Open{T}(S, o, id(dom(o)))
 end
 
 function Open{T}(o::T, m::FinFunction) where T
@@ -142,4 +146,14 @@ function oapply(CA::CospanAlgebra{Open{T}}, FA::FinSetAlgebra{T}, d::AbstractUWD
     return oapply(CA, FA, uwd_to_cospan(d), Xs)
 end
 
-end
\ No newline at end of file
+
+function draw(uwd)
+    to_graphviz(uwd, box_labels=:name, junction_labels=:variable, edge_attrs=Dict(:len => ".75"))
+end
+
+function draw_types(uwd)   # Add better typing and error catching for if uwd is untyped
+    to_graphviz(uwd, box_labels=:name, junction_labels=:junction_type, edge_attrs=Dict(:len => ".75"))
+end
+
+
+end  # module
\ No newline at end of file
diff --git a/src/Objectives.jl b/src/Objectives.jl
index 30c52bd..a853bdf 100644
--- a/src/Objectives.jl
+++ b/src/Objectives.jl
@@ -10,6 +10,8 @@ using Catlab
 import Catlab: oapply, dom
 using ForwardDiff
 using Optim
+using ComponentArrays
+
 
 # Primal Minimization Problems and Gradient Descent
 ###################################################
@@ -38,7 +40,7 @@ struct MinObj <: FinSetAlgebra{PrimalObjective} end
 The morphism map is defined by ϕ ↦ (f ↦ f∘ϕ^*).
 """
 hom_map(::MinObj, ϕ::FinFunction, p::PrimalObjective) = 
-    PrimalObjective(codom(ϕ), x->p(pullback_matrix(ϕ)*x))
+    PrimalObjective(codom(ϕ), x->p(pullback_function(ϕ, x)))
 
 """     laxator(::MinObj, Xs::Vector{PrimalObjective})
 
@@ -46,7 +48,7 @@ Takes the "disjoint union" of a collection of primal objectives.
 """
 function laxator(::MinObj, Xs::Vector{PrimalObjective})
     c = coproduct([dom(X) for X in Xs])
-    subproblems = [x -> X(pullback_matrix(l)*x) for (X,l) in zip(Xs, legs(c))]
+    subproblems = [x -> X(pullback_function(l, x)) for (X,l) in zip(Xs, legs(c))]
     objective(x) = sum([sp(x) for sp in subproblems])
     return PrimalObjective(apex(c), objective)
 end
@@ -65,7 +67,20 @@ end
 Returns the gradient flow optimizer of a given primal objective.
 """
 function gradient_flow(f::Open{PrimalObjective})
-    return Open{Optimizer}(f.S, x -> -ForwardDiff.gradient(f.o, x), f.m)
+    function f_wrapper(ca::ComponentArray)
+        inputs = [ca[key] for key in keys(ca)]
+        f.o(inputs)
+    end
+
+    function gradient_descent(x)
+        init_conds = ComponentVector(;zip([Symbol(i) for i in 1:length(x)], x)...)
+        grad = -ForwardDiff.gradient(f_wrapper, init_conds)
+        [grad[key] for key in keys(grad)]
+    end
+
+    return Open{Optimizer}(f.S, x -> gradient_descent(x), f.m)
+
+    # return Open{Optimizer}(f.S, x -> -ForwardDiff.gradient(f.o, x), f.m)   # Scalar version
 end
 
 function solve(f::Open{PrimalObjective}, x0::Vector{Float64}, ss::Float64, n_steps::Int)
@@ -101,14 +116,14 @@ struct DualComp <: FinSetAlgebra{SaddleObjective} end
 # Only "glue" along dual variables
 hom_map(::DualComp, ϕ::FinFunction, p::SaddleObjective) = 
     SaddleObjective(p.primal_space, codom(ϕ), 
-        (x,λ) -> p(x, pullback_matrix(ϕ)*λ))
+        (x,λ) -> p(x, pullback_function(ϕ, λ)))
 
 # Laxate along both primal and dual variables
 function laxator(::DualComp, Xs::Vector{SaddleObjective})
     c1 = coproduct([X.primal_space for X in Xs])
     c2 = coproduct([X.dual_space for X in Xs])
     subproblems = [(x,λ) -> 
-        X(pullback_matrix(l1)*x, pullback_matrix(l2)*λ) for (X,l1,l2) in zip(Xs, legs(c1), legs(c2))]
+        X(pullback_function(l1, x), pullback_function(l2, λ)) for (X,l1,l2) in zip(Xs, legs(c1), legs(c2))]
     objective(x,λ) = sum([sp(x,λ) for sp in subproblems])
     return SaddleObjective(apex(c1), apex(c2), objective)
 end
@@ -128,4 +143,4 @@ function gradient_flow(of::Open{SaddleObjective})
         λ -> ForwardDiff.gradient(dual_objective(f, x(λ)), λ), of.m)
 end
 
-end
\ No newline at end of file
+end  # module
\ No newline at end of file
diff --git a/src/OpenFlowGraphs.jl b/src/OpenFlowGraphs.jl
index d672139..8d12aa4 100644
--- a/src/OpenFlowGraphs.jl
+++ b/src/OpenFlowGraphs.jl
@@ -49,7 +49,7 @@ struct FG <: FinSetAlgebra{FlowGraph} end
 hom_map(::FG, ϕ::FinFunction, g::FlowGraph) =
     FlowGraph(codom(ϕ), g.edges, 
         g.src⋅ϕ, g.tgt⋅ϕ, 
-        g.edge_costs, pushforward_matrix(ϕ)*g.flows)
+        g.edge_costs, pushforward_function(ϕ, g.flows))
 
 function laxator(::FG, gs::Vector{FlowGraph})
     laxed_src = reduce(⊕, [g.src for g in gs])
diff --git a/src/Optimizers.jl b/src/Optimizers.jl
index bca291f..6fc7642 100644
--- a/src/Optimizers.jl
+++ b/src/Optimizers.jl
@@ -1,30 +1,15 @@
 # Implement the cospan-algebra of dynamical systems.
 module Optimizers
 
-export pullback_matrix, pushforward_matrix, Optimizer, OpenContinuousOpt, OpenDiscreteOpt, Euler,
-    simulate
+export Optimizer, OpenContinuousOpt, OpenDiscreteOpt, Euler,
+    simulate, pullback_function, pushforward_function
 
 using ..FinSetAlgebras
 import ..FinSetAlgebras: hom_map, laxator
 using Catlab
 import Catlab: oapply, dom
-using SparseArrays
+using ComponentArrays
 
-"""     pullback_matrix(f::FinFunction)
-
-The pullback of f : n → m is the linear map f^* : Rᵐ → Rⁿ defined by
-f^*(y)[i] = y[f(i)].
-"""
-function pullback_matrix(f::FinFunction)
-    n = length(dom(f))
-    sparse(1:n, f.(dom(f)), ones(Int,n), dom(f).n, codom(f).n)
-end
-
-"""     pushforward_matrix(f::FinFunction)
-
-The pushforward is the dual of the pullback.
-"""
-pushforward_matrix(f::FinFunction) = pullback_matrix(f)'
 
 """ Optimizer
 
@@ -46,17 +31,18 @@ struct DiscreteOpt <: FinSetAlgebra{Optimizer} end
 
 The hom map is defined as ϕ ↦ (s ↦ ϕ_*∘s∘ϕ^*).
 """
-hom_map(::ContinuousOpt, ϕ::FinFunction, s::Optimizer) = 
-    Optimizer(codom(ϕ), x->pushforward_matrix(ϕ)*s(pullback_matrix(ϕ)*x))
+function hom_map(::ContinuousOpt, ϕ::FinFunction, s::Optimizer) 
+    Optimizer(codom(ϕ), x -> pushforward_function(ϕ, s(pullback_function(ϕ, x))))
+end
 
 """     hom_map(::DiscreteOpt, ϕ::FinFunction, s::Optimizer)
 
 The hom map is defined as ϕ ↦ (s ↦ id + ϕ_*∘(s - id)∘ϕ^*).
 """
 hom_map(::DiscreteOpt, ϕ::FinFunction, s::Optimizer) =
-    Optimizer(codom(ϕ), x-> begin 
-        y = pullback_matrix(ϕ)*x
-        return x + pushforward_matrix(ϕ)*(s(y) - y)
+    Optimizer(codom(ϕ), x -> begin
+        y = pullback_function(ϕ, x)
+        return x + pushforward_function(ϕ, (s(y) - y))
     end)
 
 """     laxator(::ContinuousOpt, Xs::Vector{Optimizer})
@@ -65,10 +51,10 @@ Takes the "disjoint union" of a collection of optimizers.
 """
 function laxator(::ContinuousOpt, Xs::Vector{Optimizer})
     c = coproduct([dom(X) for X in Xs])
-    subsystems = [x -> X(pullback_matrix(l)*x) for (X,l) in zip(Xs, legs(c))]
+    subsystems = [x -> X(pullback_function(l, x)) for (X, l) in zip(Xs, legs(c))]
     function parallel_dynamics(x)
         res = Vector{Vector}(undef, length(Xs)) # Initialize storage for results
-        #=Threads.@threads=# for i = 1:length(Xs)
+        for i = 1:length(Xs)        #=Threads.@threads=#
             res[i] = subsystems[i](x)
         end
         return vcat(res...)
@@ -78,7 +64,14 @@ end
 # Same as continuous opt
 laxator(::DiscreteOpt, Xs::Vector{Optimizer}) = laxator(ContinuousOpt(), Xs)
 
+
 Open{Optimizer}(S::FinSet, v::Function, m::FinFunction) = Open{Optimizer}(S, Optimizer(S, v), m)
+Open{Optimizer}(s::Int, v::Function, m::FinFunction) = Open{Optimizer}(FinSet(s), v, m)
+
+# Special cases: m is an identity
+Open{Optimizer}(S::FinSet, v::Function) = Open{Optimizer}(S, Optimizer(S, v), id(S))
+Open{Optimizer}(s::Int, v::Function) = Open{Optimizer}(FinSet(s), v)
+
 
 # Turn into cospan-algebras.
 struct OpenContinuousOpt <: CospanAlgebra{Open{Optimizer}} end
@@ -94,11 +87,12 @@ end
 
 # Euler's method is a natural transformation from continous optimizers to discrete optimizers.
 function Euler(f::Open{Optimizer}, γ::Float64)
-    return Open{Optimizer}(f.S, Optimizer(f.S, x->x+γ*f.o(x)), f.m)
+    return Open{Optimizer}(f.S,
+     Optimizer(f.S, x -> x .+ γ .* f.o(x)), f.m)
 end
 
 # Run a discrete optimizer the designated number of time-steps.
-function simulate(f::Open{Optimizer}, x0::Vector{Float64}, tsteps::Int)
+function simulate(f::Open{Optimizer}, x0::Vector, tsteps::Int)
     res = x0
     for i in 1:tsteps
         res = f.o(res)
@@ -106,4 +100,85 @@ function simulate(f::Open{Optimizer}, x0::Vector{Float64}, tsteps::Int)
     return res
 end
 
-end
\ No newline at end of file
+# Run a discrete optimizer the designated number of time-steps.
+function simulate(f::Open{Optimizer}, d::AbstractUWD, x0::ComponentArray, tsteps::Int)
+    # Format initial conditions
+    initial_cond_vec = zeros(length(d[:variable]))
+    var_to_index = Dict()
+    curr_index = 1
+    for junction in d[:junction]
+        if !haskey(var_to_index, d[:variable][junction])
+            var_to_index[d[:variable][junction]] = curr_index
+            curr_index += 1
+        end
+    end
+
+    for (var, index) in var_to_index
+        initial_cond_vec[index] = x0[var]
+    end
+    res = initial_cond_vec
+    # Simulate
+    for i in 1:tsteps
+        res = f.o(res)
+    end
+
+    res_formatted = ComponentArray(a=1.1, b=22, c=33, d=44, e=55, f=66, g=77, h=88, i=99)
+
+    # Rebuild component array
+    for (var, index) in var_to_index
+        res_formatted[var] = res[index]
+    end
+    return res_formatted
+end
+
+function (f::Open{Optimizer})(x0::Vector)
+    return f.o(x0)
+end
+
+
+
+"""     pullback_function(f::FinFunction, v::Vector)
+
+The pullback of f : n → m is the linear map f^* : Rᵐ → Rⁿ defined by
+f^*(y)[i] = y[f(i)].
+"""
+function pullback_function(f::FinFunction, v::Vector)::Vector
+    return [v[f(i)] for i in 1:length(dom(f))]
+end
+
+
+"""     pushforward_function(f::FinFunction, v::Vector{Vector{Float64}})
+
+The pushforward of f : n → m is the linear map f_* : Rⁿ → Rᵐ defined by
+f_*(y)[j] =  ∑ y[i] for i ∈ f⁻¹(j).
+"""
+function pushforward_function(f::FinFunction, v::Vector{Vector{Float64}})::Vector
+    output = [[] for _ in 1:length(codom(f))]
+    for i in 1:length(dom(f))
+        if isempty(output[f(i)])
+            output[f(i)] = v[i]
+        else
+            output[f(i)] += v[i]
+        end
+    end
+    return output
+end
+
+
+"""     pushforward_function(f::FinFunction, v::Vector{Float64})
+
+The pushforward of f : n → m is the linear map f_* : Rⁿ → Rᵐ defined by
+f_*(y)[j] =  ∑ y[i] for i ∈ f⁻¹(j).
+"""
+function pushforward_function(f::FinFunction, v::Vector{Float64})::Vector
+    output = [0.0 for _ in 1:length(codom(f))]
+
+    for i in 1:length(dom(f))
+        output[f(i)] += v[i]
+    end
+
+    return output
+end
+
+
+end  # module
\ No newline at end of file
diff --git a/test/Objectives.jl b/test/Objectives.jl
index 615e236..5ff923e 100644
--- a/test/Objectives.jl
+++ b/test/Objectives.jl
@@ -1,8 +1,9 @@
 using AlgebraicOptimization
 using Test
 using Catlab
+using ComponentArrays
 
-# Test naturality of gradient descent
+# Test naturality of gradient descent: scalar variables
 d = @relation (x,y,z) begin
     f(w,x)
     g(u,w,y)
@@ -35,23 +36,107 @@ composite_prob = oapply(d, [p1,p2,p3])
 
 optimizer_of_composite = gradient_flow(composite_prob)
 
-o1 = gradient_flow(p1)
-o2 = gradient_flow(p2)
-o3 = gradient_flow(p3)
+o1 = Euler(gradient_flow(p1), 0.1)
+o2 = Euler(gradient_flow(p2), 0.1)
+o3 = Euler(gradient_flow(p3), 0.1)
 
-composite_of_optimizers = oapply(OpenContinuousOpt(), d, [o1,o2,o3])
+composite_of_optimizers = oapply(OpenDiscreteOpt(), d, [o1,o2,o3])
 
 dc1 = Euler(optimizer_of_composite, 0.1)
-dc2 = Euler(composite_of_optimizers, 0.1)
+dc2 = composite_of_optimizers
 
 x0 = repeat([100.0], length(composite_prob.S))
 tsteps = 1000
 r1 = simulate(dc1, x0, tsteps)
 r2 = simulate(dc2, x0, tsteps)
 
-#println(r1)
-#println(r2)
+@test r1 ≈ r2
+
+
+# Test ComponentArray version of input/output on scalar variables
+# Note that all variables must be exposed to use this i/o system
+d = @relation () begin
+    f(a, b, c, d, e)
+    g(f, g, a)
+    h(b, a, f, h)
+end
+
+P = [2.1154  -0.3038   0.368   -1.5728  -1.203
+ -0.3038   1.5697   1.0226   0.159   -0.946
+  0.368    1.0226   1.847   -0.4916  -1.2668
+ -1.5728   0.159   -0.4916   2.2192   1.5315
+ -1.203   -0.946   -1.2668   1.5315   1.9281]
+Q = [0.2456   0.3564  -0.0088
+  0.3564   0.5912  -0.0914
+ -0.0088  -0.0914   0.8774]
+R = [2.0546  -1.333   -0.5263   0.3189
+ -1.333    1.0481  -0.0211   0.2462
+ -0.5263  -0.0211   0.951   -0.7813
+  0.3189   0.2462  -0.7813   1.5813]
+
+a = [-0.26, 0.22, 0.09, 0.19, -0.96]
+b = [-0.72, 0.12, 0.41]
+c = [0.55, 0.51, 0.6, -0.61]
+
+p1 = Open{PrimalObjective}(FinSet(5), PrimalObjective(FinSet(5),x->x'*P*x + a'*x))
+p2 = Open{PrimalObjective}(FinSet(3), PrimalObjective(FinSet(3),x->x'*Q*x + b'*x))
+p3 = Open{PrimalObjective}(FinSet(4), PrimalObjective(FinSet(4),x->x'*R*x + c'*x))
+
+composite_prob = oapply(d, [p1,p2,p3])
+
+optimizer_of_composite = gradient_flow(composite_prob)
+
+o1 = Euler(gradient_flow(p1), 0.1)
+o2 = Euler(gradient_flow(p2), 0.1)
+o3 = Euler(gradient_flow(p3), 0.1)
+
+composite_of_optimizers = oapply(OpenDiscreteOpt(), d, [o1,o2,o3])
+
+dc1 = Euler(optimizer_of_composite, 0.1)
+dc2 = composite_of_optimizers
+
+
+x2 = ComponentArray(a=11, b=22, c=33, d=44, e=55, f=66, g=77, h=88, i=99)
+tsteps = 1000
+r1 = simulate(dc1, d, x2, tsteps)
+r2 = simulate(dc2, d, x2, tsteps)
 
 @test r1 ≈ r2
 
 
+# Test naturality of gradient descent: vector variables
+d = @relation (x,y,z) begin
+    f(w,x)
+    g(u,w,y)
+    h(u,w,z)
+end
+
+f1 = x -> x[1][3] + x[4][1] - x[3][2] / x[2][1]
+f2 = x -> 22 * x[2][2] / x[3][1]
+f3 = x -> sum(sum(v) for v in x)
+
+p1 = Open{PrimalObjective}(FinSet(5), PrimalObjective(FinSet(5), f1), FinFunction([2,4], 5))
+p2 = Open{PrimalObjective}(FinSet(3), PrimalObjective(FinSet(3), f2), id(FinSet(3)))
+p3 = Open{PrimalObjective}(FinSet(4), PrimalObjective(FinSet(4), f3), FinFunction([1,3,4]))
+
+composite_prob = oapply(d, [p1,p2,p3])
+
+optimizer_of_composite = gradient_flow(composite_prob)
+
+o1 = Euler(gradient_flow(p1), 0.1)
+o2 = Euler(gradient_flow(p2), 0.1)
+o3 = Euler(gradient_flow(p3), 0.1)
+
+composite_of_optimizers = oapply(OpenDiscreteOpt(), d, [o1,o2,o3])
+
+dc1 = Euler(optimizer_of_composite, 0.1)
+dc2 = composite_of_optimizers
+
+x1::Vector{Vector{Float64}} = [[1, 1, 2], [2, 2], [3, 3], [4, 4], [1, 1], [2], [3], [4, 40, 40], [5]]   
+
+
+tsteps = 1000
+r1 = simulate(dc1, x1, tsteps)
+r2 = simulate(dc2, x1, tsteps)
+
+@test r1 ≈ r2
\ No newline at end of file
diff --git a/test/OpenFlowGraphs.jl b/test/OpenFlowGraphs.jl
index 6c5c252..c1c8662 100644
--- a/test/OpenFlowGraphs.jl
+++ b/test/OpenFlowGraphs.jl
@@ -1,8 +1,13 @@
 using Test
 using AlgebraicOptimization
+using Catlab
 
 
-
+d = @relation (x,y,z) begin
+    f(w,x)
+    g(u,w,y)
+    h(u,w,z)
+end
 
 g = random_open_flowgraph(10, .2, 3)
 A = node_incidence_matrix(data(g))
diff --git a/test/Optimizers.jl b/test/Optimizers.jl
index f9e6c57..1780ccc 100644
--- a/test/Optimizers.jl
+++ b/test/Optimizers.jl
@@ -2,8 +2,8 @@ using AlgebraicOptimization
 using Catlab
 using Test
 
-# Test naturality of Euler
-d = @relation (x,y,z) begin
+# Test naturality of Euler with scalar functions
+d = @relation (x,y,z,u,w) begin
     f(w,x)
     g(u,w,y)
     h(u,w,z)
@@ -13,7 +13,7 @@ A = rand(-1:0.01:1,5,5)
 B = rand(-1:0.01:1,3,3)
 C = rand(-1:0.01:1,4,4)
 
-o1 = Open{Optimizer}(FinSet(5), x->A*x, FinFunction([2,4], 5))
+o1 = Open{Optimizer}(FinSet(5), x->A*x, FinFunction([2,4], 5) )
 o2 = Open{Optimizer}(FinSet(3), x->B*x, id(FinSet(3)))
 o3 = Open{Optimizer}(FinSet(4), x->C*x, FinFunction([1,3,4]))
 
@@ -28,14 +28,80 @@ do3 = Euler(o3, 0.01)
 composite_of_discretizations = oapply(OpenDiscreteOpt(), d, [do1,do2,do3])
 
 x0 = repeat([1.0], length(composite_opt.S))
+
 tsteps = 100
 r1 = simulate(discretization_of_composites, x0, tsteps)
 r2 = simulate(composite_of_discretizations, x0, tsteps)
 
-#println(r1)
-#println(r2)
+@test r1 ≈ r2
+
+
+
+# Test naturality of Euler with vector functions
+d = @relation (x,y,z,u,w,) begin
+    f(w,x)
+    g(u,w,y)
+    h(u,w,z)
+end
+
+
+mA = v -> [[v[1][1]],  [v[2][1], v[1][1]], [v[3][2], v[3][1], v[4][4]],  [v[4][4], v[3][1], v[2][1], v[1][1]], [5, 5, 5, 5, 10]]
+mB = v -> [[6, 6, 6, 6, 6, 6], [2, 2], [7, 7, 7, 7, 7, 7, 7]]
+mC = v -> v
+
+o1 = Open{Optimizer}(FinSet(5), mA, FinFunction([2,4], 5))
+o2 = Open{Optimizer}(FinSet(3), mB, id(FinSet(3)))
+o3 = Open{Optimizer}(FinSet(4), mC, FinFunction([1,3,4]))
+
+composite_opt = oapply(OpenContinuousOpt(), d, [o1,o2,o3])
+
+discretization_of_composites = Euler(composite_opt, 0.01)
+
+do1 = Euler(o1, 0.01)
+do2 = Euler(o2, 0.01)
+do3 = Euler(o3, 0.01)
+
+
+composite_of_discretizations = oapply(OpenDiscreteOpt(), d, [do1,do2,do3])
+
+x1::Vector{Vector{Float64}} = [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7, 8], [1, 2, 3, 4, 5, 6, 7, 8, 9]]
+tsteps = 100
+r1 = simulate(discretization_of_composites, x1, tsteps)
+r2 = simulate(composite_of_discretizations, x1, tsteps)
 
 @test r1 ≈ r2
 
 
+# Test ComponentArray version of input/output
+
+d = @relation () begin
+    f(a, b, c, d, e)
+    g(f, g, a)
+    h(b, a, f, h)
+end
+
+A = rand(-1:0.01:1,5,5)
+B = rand(-1:0.01:1,3,3)
+C = rand(-1:0.01:1,4,4)
+
+o1 = Open{Optimizer}(FinSet(5), x->A*x)
+o2 = Open{Optimizer}(FinSet(3), x->B*x)
+o3 = Open{Optimizer}(FinSet(4), x->C*x)
+
+composite_opt = oapply(OpenContinuousOpt(), d, [o1,o2,o3])
+
+discretization_of_composites = Euler(composite_opt, 0.01)
+
+do1 = Euler(o1, 0.01)
+do2 = Euler(o2, 0.01)
+do3 = Euler(o3, 0.01)
+
+composite_of_discretizations = oapply(OpenDiscreteOpt(), d, [do1,do2,do3])
+
+x2 = ComponentArray(a=11, b=22, c=33, d=44, e=55, f=66, g=77, h=88, i=99)
+
+tsteps = 100
+r1 = simulate(discretization_of_composites, d, x2, tsteps)
+r2 = simulate(composite_of_discretizations, d, x2, tsteps)
 
+@test r1 ≈ r2
\ No newline at end of file
diff --git a/test/Project.toml b/test/Project.toml
index 99e2389..d5a8a2b 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,6 +1,7 @@
 [deps]
-AlgebraicOptimization = "a72ceada-00ec-4ad9-90d3-37b40eaed052"
-Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 AlgebraicDynamics = "5fd6ff03-a254-427e-8840-ba658f502e32"
+AlgebraicOptimization = "a72ceada-00ec-4ad9-90d3-37b40eaed052"
 Catlab = "134e5e36-593f-5add-ad60-77f754baafbe"
+ComponentArrays = "b0b7db55-cfe3-40fc-9ded-d10e2dbeff66"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"