Long stack trace, identify precise error location

General Usage
1

I am trying to solve a UODE where the neural network uses a tensor-basis neural net. Here are the first few lines of my stack trace (the details are not important since I am not asking you to debug my code :slight_smile: ):

ERROR: MethodError: no method matching init(::Nothing, ::Tsit5{typeof(OrdinaryDiffEq.trivial_limiter!), typeof(OrdinaryDiffEq.trivial_limiter!), Static.False}; sensealg::InterpolatingAdjoint{0, true, Val{:central}, ReverseDiffVJP{true}}, saveat::Float64)

Closest candidates are:
  init(::OptimizationProblem, ::Any, ::Any...; kwargs...)
   @ SciMLBase ~/.julia/packages/SciMLBase/VdcHg/src/solve.jl:146
  init(::PDEProblem, ::SciMLBase.AbstractDEAlgorithm, ::Any...; kwargs...)
   @ DiffEqBase ~/.julia/packages/DiffEqBase/ihYDa/src/solve.jl:1011
  init(::SciMLBase.AbstractJumpProblem, ::Any...; kwargs...)
   @ DiffEqBase ~/.julia/packages/DiffEqBase/ihYDa/src/solve.jl:441
  ...

Stacktrace:
  [1] macro expansion
    @ ~/.julia/packages/Zygote/SuKWp/src/compiler/interface2.jl:0 [inlined]
  [2] _pullback(::Zygote.Context{false}, ::typeof(Core.kwcall), ::NamedTuple{(:sensealg, :saveat), Tuple{InterpolatingAdjoint{0, true, Val{:central}, ReverseDiffVJP{true}}, Float64}}, ::typeof(init), ::Nothing, ::Tsit5{typeof(OrdinaryDiffEq.trivial_limiter!), typeof(OrdinaryDiffEq.trivial_limiter!), Static.False})
    @ Zygote ~/.julia/packages/Zygote/SuKWp/src/compiler/interface2.jl:9
  [3] _apply(::Function, ::Vararg{Any})
    @ Core ./boot.jl:838

The first line is clear enough:

ERROR: MethodError: no method matching init(::Nothing, ::Tsit5{typeof(OrdinaryDiffEq.trivial_limiter!), typeof(OrdinaryDiffEq.trivial_limiter!), Static.False}; sensealg::InterpolatingAdjoint{0, true, Val{:central}, ReverseDiffVJP{true}}, saveat::Float64)

I followed the very long trace, and I did not find the specific line where this function was executed, and therefore, the error is hard to fix. Given the very long trace, it is hard to believe that this line is not available to the stack trace.

Perhaps there is too much inlining going on. Is it possible to run Julia from the command line with options such that inlining is disabled? That might help. Thanks.

2

Hard to tell without any code, but it sounds like you did solve(nothing, Tsit5()) somewhere instead of passing an ODEProblem?

3

Of course, what you say is logical, but if it is the case, it is not obvious at all. That is the problem with using high-level interface. The error is happening somewhere within my Ensemble functions. To solve the problem, you鈥檇 have to see the entire code, but I should create a MWE, which again, will take time. I have decided to learn how to use Debugging.jl.

4

Perhaps relevant: There are several packages, such as RelevanceStrackTraces.jl that are designed to make it easier to find the place in the user code that caused the exception to be thrown.

5

Thank you. I had not heard of this. Of course, I鈥檒l try it out.
So far, I have been unsuccessful in my attempts to use Debugger.jl.

6

What I generally do in cases of deeply nested calls is to find the first item in the stacktrace where one of my functions occurs. RelevanceStrackTraces is designed to point to that place clearly.
Then I insert an @assert !isnothing(x) type of statement there (which I just keep unless the code is really performance critical). Then I work my way backwards through the stacktrace.
I have not had much luck with the debugger, but I rarely miss it.

7

I have a question. When getting a stack trace that starts of as:

ERROR: MethodError: no method matching (::Chain{Tuple{Dense{typeof(tanh), Matrix{Float32}, 鈥, Dense{typeof(identity), Matrix{Float32}, 鈥}})(::Vector{Float64}, ::Vector{Float32})
Closest candidates are:
  (::Chain)(::Any)
   @ Flux ~/.julia/packages/Flux/FWgS0/src/layers/basic.jl:51

Stacktrace:
   [1] tbnn_opt(蟽::Matrix{Float32}, D::SMatrix{3, 3, Float64, 9}, model_weights::Vector{Float32}, model_univ::Chain{Tuple{Dense{typeof(tanh), Matrix{Float32}, 鈥, Dense{typeof(identity), Matrix{Float32}, 鈥}}, t::Float32)
     @ Main ~/src/2022/rude/giesekus/GE_rude.jl/alex_report_code_2023-03-24/julia19/rude_giesekus_optimized_reduced_scalar.jl:67
   [2] dudt_univ_opt!(

would it be hard to provide the line number and file that generated the error starting with

ERROR: MethodError: no method matching (::Chain{Tuple{Dense{typeof(tanh), Matrix{Float32}, 鈥, Dense{typeof(identity), Matrix{Float32}, 鈥}})(::Vector{Float64}, ::Vector{Float32})

Why can鈥檛 the information be provided on the very same line together with a link. Isn鈥檛 this information available? I still have not figured out which function generated my original message let alone this one. Thanks.

8

I fee your pain with the inscrutable stack traces.
The debugger is simple to use (not saying it鈥檚 very good) from Visual Studio Code. Just do
@run your_command and it will stop somewhere, than you can follow the stacktrace on the left side till you find the point where the error originated.

9

@run does not work in REPL.
I love Julia, but it is not written with ease of use in mind. I absolutely do not understand why Julia does not have built in options to manipulate the stack traces in useful ways. Even the long traces shouldn鈥檛 be the default. The original error should clearly state what file and what line it occurred (or a range of lines). Sorry for the rant.

10

Maybe I鈥檓 misunderstanding your question, but isn鈥檛 this what

is showing? The second line starting with @ there shows (in order) the module, file name and line number on which the error occurred.

11

I said from Visual Studio Code (it鈥檚 own REPL). But it does also from the normal REPL if you install Debugger package, though I鈥檝e no experience with it.

12

the debugger is indeed simple to attempt to use, but as far as my experience attempting goes, it doesn鈥檛 work particularly well (to the extent where I end up just returning to print debugging)

13

@TouchSir,

No. The line that says tbnn is one of my function calls. There is no reference to Chain on that line.

14

Oh I see. So that line is actually part of the MethodError error message and not the stacktrace, though I can see why it might be confusing if you鈥檙e not familiar with the error format.

How to interpret this is that at rude_giesekus_optimized_reduced_scalar.jl:67, tbnn_opt calls a Chain struct. You should be able to confirm that by looking at the line in question. no method matching (::Chain{Tuple{Dense{typeof(tanh), Matrix{Float32}, 鈥, Dense{typeof(identity), Matrix{Float32}, 鈥}})(::Vector{Float64}, ::Vector{Float32}) looks intimidating, but that鈥檚 mostly because the type parameters take up a lot of space. If we remove them, that line becomes no method matching (::Chain)(::Vector{Float64}, ::Vector{Float32}).

As you can tell, Flux.Chain only accepts one argument when called, so something is erroneously passing two. The MethodError message tries to help here by referencing (::Chain)(::Any) (note one arg only) and linking to its definition here so you can investigate further.

15

Thanks for the feedback. I do know how to interpret a trace, or thought I did. Concerning Chain and the fact that it has only one argument, I beg to differ. Running methods Flux.Chain, I get the result:

methods(Flux.Chain)
# 3 methods for type constructor:
 [1] Chain(; kw...)
     @ ~/.julia/packages/Flux/FWgS0/src/layers/basic.jl:40
 [2] Chain(layers::T) where T<:Union{Tuple, NamedTuple, AbstractVector}
     @ ~/.julia/packages/Flux/FWgS0/src/layers/basic.jl:36
 [3] Chain(xs...)
     @ ~/.julia/packages/Flux/FWgS0/src/layers/basic.jl:39

Doesn鈥檛 the third choice (and even the second) imply that multiple arguments are accepted, contrary to what the error message implies?

16

@ToucheSir : Here is some of my code:

function tbnn_opt(蟽, D, model_weights, model_univ, t)
    # Compute elements of the tensor basis
    I  = SA[1. 0. 0.; 0. 1. 0.; 0. 0. 1.]

    # Compute the integrity basis from scalar invariants. Traces. 
    位 = zeros(1) # must be mutale
    位[1] = tr(蟽)
    println("input to NN, 位: ", 位)
    g = model_univ(位, model_weights)    ### Error
    F = g[1] .* I 
end

# NN model for the nonlinear function F(蟽,纬虈)
model_univ = Flux.Chain(Flux.Dense(1, 8, tanh),
                       Flux.Dense(8, 1))
p_model, re = Flux.destructure(model_univ)

# Parameters of the linear response (畏0,蟿)
p_system = Float32[1, 1]

Yes, I am using Julia 1.9, and so should be using Lux. But surely Flux has not been deprecated, right?

Look at the page: Built-in Layers 路 Flux, the stable version of Flux.jl . Tons of examples where Flux.Chain take multiple arguments. So I still do not undertand the error.

17

The constructor mymodel = Chain(layer1, layer2, ...) takes multiple arguments. Calling that model mymodel(x) takes just one. I鈥檓 not sure what model_weights and model_univ are meant to be in tbnn_opt because you generally wouldn鈥檛 separate model structure from weights in Flux, so this seems like a better question for one of the SciML help channels.

This also seems like something specific to only SciML and should likewise be asked there :slight_smile:

18

Ok, will think some more and do that. I have never posted to specific channels yet.