I’ve been stuck trying to get a variational autoencoder working using Flux. I’ve tried to adapt the mnist VAE in Flux’s model zoo (which I could not get to work either) to the iris data set.

Here’s my code so far:

```
using Distributions
using Flux
using Flux: params, logitbinarycrossentropy
using Flux: Data.DataLoader
using Flux: Losses
using RDatasets
X = dataset("datasets", "iris");
select!(X, Not(:Species));
X = transpose(convert(Matrix, X));
loader = DataLoader(X, batchsize=1, shuffle=true);
eH1 = Dense(16, 32)
eH2 = Dense(16, 32)
encoder = Chain(Dense(4, 16, relu),
x -> (eH1(x), eH2(x)))
decoder = Chain(Dense(32, 16),
Dense(16, 4))
function reparameterize(μ, logvar)
std = exp.(logvar ./ 2)
eps = rand(MvNormal(vec(fill(0., 32)), vec(std)))
uu = μ .+ eps .* std
uu, μ, logvar
end
model = Chain(x -> encoder(x),
x -> reparameterize(x[1], x[2]),
x -> (decoder(x[1]), x[2], x[3]))
function loss(x)
x̂, μ, logvar = model(x)
reconst_loss = sum(Losses.logitbinarycrossentropy.(x̂, x))
kl_div = -0.5 * sum(1. .+ logvar .- μ.^2 .- exp.(logvar))
reconst_loss + kl_div
end
ps = Flux.Params(model)
opt = ADAM()
Flux.train!(loss, ps, loader, opt)
```

Here’s the error:

```
julia> Flux.train!(loss, ps, loader, opt)
ERROR: Mutating arrays is not supported
Stacktrace:
[1] error(::String) at ./error.jl:33
[2] (::Zygote.var"#368#369")(::Nothing) at /Users/rs990e/.julia/packages/Zygote/ggM8Z/src/lib/array.jl:61
[3] (::Zygote.var"#2255#back#370"{Zygote.var"#368#369"})(::Nothing) at /Users/rs990e/.julia/packages/ZygoteRules/OjfTt/src/adjoint.jl:59
[4] materialize! at ./broadcast.jl:848 [inlined]
[5] materialize! at ./broadcast.jl:845 [inlined]
[6] materialize! at ./broadcast.jl:841 [inlined]
[7] broadcast! at ./broadcast.jl:814 [inlined]
```

I’m not sure which array is being modified. Any suggestions?

Here’s my env info:

```
(@v1.5) pkg> st
Status `~/.julia/environments/v1.5/Project.toml`
[31c24e10] Distributions v0.24.12
[587475ba] Flux v0.11.1
[ce6b1742] RDatasets v0.7.4
[e88e6eb3] Zygote v0.5.17
```