# What's wrong with this Flux model definitin?
**URL:** https://discourse.julialang.org/t/whats-wrong-with-this-flux-model-definitin/30816
**Category:** Machine Learning
**Tags:** first-steps, flux
**Created:** [November 7, 2019, 3:00am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-flux-model-definitin/30816 "2019-11-07T03:00:00Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [November 7, 2019, 3:00am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-flux-model-definitin/30816/1 "2019-11-07T03:00:00Z")
I am on the latest master branch of `Flux.jl`
```julia
using Flux
using CuArrays
CuArrays.allowscalar(false)
x = gpu(rand(Float32, 1_000_000, 2))
y = 2 .* x + gpu(rand(Float32, 1_000_000))
w = gpu(rand(2, 1))
loss(x, y) = Flux.mse(x*w,y)
Flux.train!(loss, w, ((x,y),), ADAM())
```
I am trying to train a simple linear model. But I keep getting scalar error.
```julia-repl
ERROR: scalar getindex is disallowed
Stacktrace:
[1] error(::String) at ./error.jl:33
[2] assertscalar(::String) at /home/zj/.julia/packages/GPUArrays/0lvhc/src/indexing.jl:14
[3] getindex at /home/zj/.julia/packages/GPUArrays/0lvhc/src/indexing.jl:54 [inlined]
[4] iterate at ./abstractarray.jl:914 [inlined]
[5] iterate(::CuArray{Float32,2,Nothing}) at ./abstractarray.jl:912
[6] Params at /home/zj/.julia/packages/Zygote/8dVxG/src/compiler/interface.jl:73 [inlined]
[7] #train!#12(::Flux.Optimise.var"#16#22", ::typeof(Flux.Optimise.train!), ::Function, ::CuArray{Float32,2,Nothing}, ::Tuple{Tuple{CuArray{Float32,2,Nothing},CuArray{Float32,1,Nothing}}}, ::ADAM) at /home/zj/.julia/dev/Flux/src/optimise/train.jl:64
[8] train!(::Function, ::CuArray{Float32,2,Nothing}, ::Tuple{Tuple{CuArray{Float32,2,Nothing},CuArray{Float32,1,Nothing}}}, ::ADAM) at /home/zj/.julia/dev/Flux/src/optimise/train.jl:64
[9] top-level scope at REPL[26]:100:
```
It seems ot be saying iterate is the issue, but where is the issue? Is it iterating through `x`? How to debug this?
---
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [November 7, 2019, 3:13am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-flux-model-definitin/30816/2 "2019-11-07T03:13:57Z")
> [@xiaodai](#):
>
> Flux.train!(loss, w, ((x,y),), ADAM())
The errors seems to be not wrapping `w` in `params`. So this works
```julia
using Flux
using CuArrays
CuArrays.allowscalar(false)
x = gpu(rand(Float32, 1_000_000, 2))
y = x*gpu([2, 2]) + gpu(rand(Float32, 1_000_000))
w = gpu(rand(Float64, 2, 1))
loss(x, y) = Flux.mse(x*w,y) |> gpu
Flux.train!(loss, params(w), ((x,y),), ADAM())
```