# Build\_function: stack overflow in type inference

**URL:** <https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971>\
**Category:** Modelling & Simulations\
**Created:** [February 9, 2024, 8:46am UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971 "2024-02-09T08:46:29Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Johan-Gronqvist](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johan-gronqvist/32/29895_2.png) [@Johan-Gronqvist](https://discourse.julialang.org/u/Johan-Gronqvist)\
**Post date:** [February 9, 2024, 8:46am UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971/1 "2024-02-09T08:46:29Z")

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I am trying to use `Symbolics.build_function` to generate `JuMP.AffExpr` expressions from symbolic expressions.

I see an error message

```julia
Internal error: stack overflow in type inference of (::RuntimeGeneratedFunctions.RuntimeGeneratedFunction{(:ˍ₋arg1, :ˍ₋arg2, :ˍ₋arg3, :λ_slope, :λ_sector, :P, :ζ²), Symbolics.var"#_RGF_ModTag", Symbolics.var"#_RGF_ModTag", (0xc10ed7fe, 0x47ee3867, 0xeabcab9f, 0x039a29c4, 0x30209ded), Expr})(Array{JuMP.GenericAffExpr{Float64, JuMP.GenericVariableRef{Float64}}, 2}, Array{JuMP.GenericAffExpr{Float64, JuMP.GenericVariableRef{Float64}}, 2}, Array{JuMP.GenericAffExpr{Float64, JuMP.GenericVariableRef{Float64}}, 2}, JuMP.GenericVariableRef{Float64}, JuMP.GenericVariableRef{Float64}, Array{JuMP.GenericVariableRef{Float64}, 2}, Float64).
This might be caused by recursion over very long tuples or argument lists.

```

I would like to understand what measure of complicatedness is problematic for `build_function` and how well I should expect it to scale. (There was a thread [1] earlier with a comment that mentioned “tens of thousands of variables” as a notion of a large function, and I have much fewer than that.)

As can be seen in the error message, the function has only 7 arguments and those are mostly matrices of JuMP expressions. The matrices used as arguments are not very large (diagonal matrices of size around 30x30 or dense of size 4x4). `Symbolics.substitute` replaces the variables in around 4 seconds, and I was hoping for `build_function` to offer a faster alternative as I want to perform the same optimization many times while varying parameter values and on new JuMP models.

(I suspect the right solution to my problem may involve reusing JuMP models instead, and replacing parameters in those, but this questions is one step along the way of testing different options, and I have not yet looked for information on reusing JuMP models.)

[1] [Compiling large Symbolics.jl expressions using build\_function - #3 by ChrisRackauckas](https://discourse.julialang.org/t/compiling-large-symbolics-jl-expressions-using-build-function/97563/3)

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<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [February 9, 2024, 9:07am UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971/2 "2024-02-09T09:07:38Z")

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Make a post with your real question. You should be able to do this all in JuMP. You wont need to use symbolics.

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [February 9, 2024, 11:44am UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971/3 "2024-02-09T11:44:44Z")

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Are you using symbolic array expressions? You should make sure that your function isn’t scalarizing. Share some code.

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<div class="post-metadata">

**Author:** ![Johan-Gronqvist](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johan-gronqvist/32/29895_2.png) [@Johan-Gronqvist](https://discourse.julialang.org/u/Johan-Gronqvist)\
**Post date:** [February 9, 2024, 12:43pm UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971/4 "2024-02-09T12:43:01Z")

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I have tried using symbolic arrays and symbolic array expressions, but I had problems [1] where `substitute` and `build_function` both failed to replace all occurences of the variables, and I therefore started to `scalarize` my expressions to obtain correct results.

I now sometimes define symbolic arrays, but I always scalarize them before using them in mathematical operations.

By the way, I never spent enough time debugging my issues with symbolic arrays, but I think some may have been related to `getindex` expressions like `(broadcast(-, K))[1, 2]` perhaps being considered non-composite expressions, due to [2].

[1] [Symbolics build\_function issues on complicated expressions](https://discourse.julialang.org/t/symbolics-build-function-issues-on-complicated-expressions/109727)

[2] In Symbolics.jl, in the file `utils.jl`, getindex operations are all treated the same, regardless of the complexity of the argument to `getindex`, in the following function.

```julia
function is_singleton(e)
    if istree(e)
        op = operation(e)
        op === getindex && return true
        istree(op) && return is_singleton(op) # recurse to reach getindex for array element variables
        return issym(op)
    else
        return issym(e)
    end
end

```

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<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [February 9, 2024, 9:23pm UTC](https://discourse.julialang.org/t/build-function-stack-overflow-in-type-inference/109971/5 "2024-02-09T21:23:23Z")

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Can you provide a reproducible example? Its much easier to offer specific advice than general.