"size(x) == size(x̄) ? x̄ :" can not take the size, only length

[lisa-dot]

Hello, I have written a loss function that Zygote cannot handle:
`function loss_ungelabelt2(X,Y)

a_list = Float32[]
b_list = Float32[]
mix_res = Float32[]

λ::Float32 = 0.3
loss::Float32 = 0

for i in 1:2  #eigentlich size(X,4)  
    a = X[:,:,:,rand(1:size(X,4))] 
    b = X[:,:,:,rand(1:size(X,4))]
    println(size(a))
    mix = λ .* a .+ (1 - λ) .* b
    println(length(mix))
    println(size(mix))
    println("NEU")
    mix_res=reshape([mix_res...,mix...],size(mix)...,:) # einzelne Elemente 
    a_list=reshape([a_list...,a...],size(a)...,:)
    b_list=reshape([b_list...,b...],size(b)...,:)
    println(size(mix_res))
    println(length(mix_res))
    println("neueRunde")
    
    
end
y_mix = model(mix_res)
y_a = model(a_list)
y_b = model(b_list)
println("a", size(y_a))
println("b", size(y_b))
y_mix_ab =  λ .* y_a .+ (1 - λ) .* y_b 
println(length(y_mix_ab))

quadrat_loss = sum(abs2,y_mix .- y_mix_ab)

return quadrat_loss

end

Error: MethodError: no method matching size(::NTuple{784,Float32})
Closest candidates are:
size(::Tuple, !Matched::Integer) at tuple.jl:22
size(!Matched::Flux.OneHotVector) at /Users/lisa/.julia/packages/Flux/IjMZL/src/onehot.jl:8
size(!Matched::ZMQ.Message) at /Users/lisa/.julia/packages/ZMQ/R3wSD/src/message.jl:95
...

Stacktrace:
[1] unbroadcast(::Array{Float32,3}, ::NTuple{784,Float32}) at /Users/lisa/.julia/packages/Zygote/seGHk/src/lib/broadcast.jl:53
[2] (::Zygote.var"#1107#1109"{NTuple{784,Float32}})(::Array{Float32,3}) at /Users/lisa/.julia/packages/Zygote/seGHk/src/lib/broadcast.jl:74
[3] map(::Zygote.var"#1107#1109"{NTuple{784,Float32}}, ::Tuple{Array{Float32,3},Array{Float32,3}}) at ./tuple.jl:158
[4] (::Zygote.var"#1106#1108"{Tuple{Array{Float32,3},Array{Float32,3}}})(::NTuple{784,Float32}) at /Users/lisa/.julia/packages/Zygote/seGHk/src/lib/broadcast.jl:74
[5] (::Zygote.var"#3852#back#1110"{Zygote.var"#1106#1108"{Tuple{Array{Float32,3},Array{Float32,3}}}})(::NTuple{784,Float32}) at /Users/lisa/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
[6] loss_ungelabelt2 at ./In[13]:14 [inlined]
[7] (::typeof(∂(loss_ungelabelt2)))(::Float32) at /Users/lisa/.julia/packages/Zygote/seGHk/src/compiler/interface2.jl:0
[8] (::Zygote.var"#41#42"{typeof(∂(loss_ungelabelt2))})(::Float32) at /Users/lisa/.julia/packages/Zygote/seGHk/src/compiler/interface.jl:45
[9] gradient(::Function, ::Array{Float32,4}, ::Vararg{Any,N} where N) at /Users/lisa/.julia/packages/Zygote/seGHk/src/compiler/interface.jl:54
[10] top-level scope at In[14]:1
[11] include_string(::Function, ::Module, ::String, ::String) at ./loading.jl:1091`

Someone told me that this is a Zygote bug:
"The error is this line

Zygote.jl/src/lib/broadcast.jl

Line 52 in ed366f3

size(x) == size(x̄) ? x̄ :

where zygote tries to take size(x̄)
x̄ is turning out to be a Tuple which don’t have size defined on them.
Only length.
However, that is just a symptom, as that line should be fine,
because if x is an Array,
then x̄ should also be an Array.

So something is going wrong somewhere else that is causing it to be a Tuple."

If this was the case, I would be grateful if it could be fixed. Since I am currently writing my bachelor thesis and need the code for it.

[mcabbott]

Might be #599 again?

But avoiding splatting things of length 784 would be a good idea too, even without Zygote involved. Isn't [a_list...,a...] just vcat(a_list, a)?

[lisa-dot]

I usually work less with Julia and am therefore rather inexperienced. I think instead of [a_list...,a...] I can also use vcat(a_list, a).

[mcabbott]

Sure, it's hard to know the best way the first time. And doing strange things is a good to find bugs like this one, ideally this ought to work.

[DhairyaLGandhi]

In some ways pushing people to not jump into performance sinks like this would be, is a nice thing, but that's just me.

Does vcat work?

[lisa-dot]

vcat works for a_list and b_list, not for mix_res. But unfortunately this does not fix my error.

[DhairyaLGandhi]

You might need vec for that

[lisa-dot]

vec would also not work.
vec -> MethodError: no method matching vec(::Array{Float32,1}, ::Array{Float32,3})
vcat -> DimensionMismatch("cannot broadcast array to have fewer dimensions")