# StackOverflowError when training a neural network

**URL:** <https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224>\
**Category:** New to Julia\
**Tags:** flux, stackoverflow, neural-network\
**Created:** [July 14, 2022, 3:14pm UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224 "2022-07-14T15:14:00Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![jpt](https://avatars.discourse-cdn.com/v4/letter/j/58f4c7/32.png) [@jpt](https://discourse.julialang.org/u/jpt)\
**Post date:** [July 14, 2022, 3:14pm UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/1 "2022-07-14T15:14:00Z")

</div>

I am training a Neural network using the Flux library. The definition of the neural network is as follows:

```julia
NN = Flux.Chain(
        Flux.Dense(13, 32, sigmoid),
        Flux.Dense(32, 32, sigmoid),
        Flux.Dense(32, 5),
        y->abs.(y))

```

It used to be working previously, I was able to run the training for 2000 iterations. But suddenly, from today, I am getting a StackOverflowError. I did not change anything in the code. I have tried restarting the PC, and also tried the execution in another PC. Still the same error. The error does not even have a stack trace.

```julia
ERROR: StackOverflowError:

```

The package status is as follows:

```julia
Project.toml`
  [fbb218c0] BSON v0.3.5
  [4ec6fef6] Bezier v0.1.7
  [41bf760c] DiffEqSensitivity v6.79.0   
  [0c46a032] DifferentialEquations v7.1.0
  [6a86dc24] FiniteDiff v2.13.0
  [587475ba] Flux v0.13.3
  [f6369f11] ForwardDiff v0.10.30        
  [91a5bcdd] Plots v1.30.2
  [e88e6eb3] Zygote v0.6.40

```

Version info:

```julia
Julia Version 1.7.3
Commit 742b9abb4d (2022-05-06 12:58 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: Intel(R) Core(TM) i5-8365U CPU @ 1.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, skylake)
Environment:
  JULIA_EDITOR = code
  JULIA_NUM_THREADS =

```

As the error has no further description, it is difficult to identify which variable/operation is causing the StackOverflow. Any advice on possible causes / troubleshotting methods?

---

<div class="post-metadata">

**Author:** ![mcabbott](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mcabbott/32/6603_2.png) [@mcabbott](https://discourse.julialang.org/u/mcabbott)\
**Post date:** [July 14, 2022, 3:27pm UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/2 "2022-07-14T15:27:19Z")

</div>

Can you post the stack trace from the error? And perhaps versions from `using Pkg; Pkg.status()` and from `versioninfo()`?

---

<div class="post-metadata">

**Author:** ![jpt](https://avatars.discourse-cdn.com/v4/letter/j/58f4c7/32.png) [@jpt](https://discourse.julialang.org/u/jpt)\
**Post date:** [July 14, 2022, 3:33pm UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/3 "2022-07-14T15:33:46Z")

</div>

I have updated in the original post

---

<div class="post-metadata">

**Author:** ![jmair](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jmair/32/35117_2.png) [@jmair](https://discourse.julialang.org/u/jmair)\
**Post date:** [July 15, 2022, 7:15am UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/4 "2022-07-15T07:15:26Z")

</div>

Does the error stack trace tell you the line numbers or at least the function where this is failing? We would need to see the code that causes the error.

---

<div class="post-metadata">

**Author:** ![jpt](https://avatars.discourse-cdn.com/v4/letter/j/58f4c7/32.png) [@jpt](https://discourse.julialang.org/u/jpt)\
**Post date:** [July 15, 2022, 8:08am UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/5 "2022-07-15T08:08:39Z")

</div>

Here’s a reduced version of the code. X1 and X2 vectors are populated with values from the training data, with `n_pts = 585` and `n_cases = 1276`.

```julia
X1 = zeros(13, n_pts * n_cases)
X2 = zeros(5, n_pts * n_cases)
i = 0
for ics in 1:n_cases, ipt in 1:n_pts
    i += 1
    X1[:, i] = vcat(xyz[ipt, ics, :], uparams[ics, :], wa[ics])
    X2[:, i] = pp[ipt, ics, :]
end

loss_new(X1, X2, NN) = sum(abs2, NN(X1) - X2)
function loss4()
    return loss_new(X1, X2, NN)
end

# Training
data = Iterators.repeated((), 1000)
opt = Flux.ADAM(0.01, (0.9, 0.99))
Flux.train!(loss4, Flux.params(NN), data, opt, cb=cb)

```

```julia
ERROR: StackOverflowError:

```

The stack trace does not even tell the line number where the error occurs. But, if I run the code line-by-line, the error occurs at the last line - during the Flux.train. No further details unfortunately.

---

<div class="post-metadata">

**Author:** ![jmair](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jmair/32/35117_2.png) [@jmair](https://discourse.julialang.org/u/jmair)\
**Post date:** [July 16, 2022, 7:10am UTC](https://discourse.julialang.org/t/stackoverflowerror-when-training-a-neural-network/84224/6 "2022-07-16T07:10:24Z")

</div>

I think the issue is likely to be the loss function, try using one of the inbuilt flux loss functions:  
[Flux Losses](https://fluxml.ai/Flux.jl/stable/models/losses/)

You can try and run your current loss normally in the REPL to see if it works as expected, but I imagine it should look like:

```julia
sum(abs2.(NN(X1) .- X2))

```

I would suggest changing the train line to something like:

```julia
data=Iterators.repeated((X1,X2), 1000)
loss(x, y)=Flux.Losses.mse(NN(x),y)
Flux.train!(loss, params(NN), data, opt, cb=cb)

```

I am not able to run the code now, so you may need to tweak the code above to get it to work, but see if that helps.