# Generate code from Symbolics.jl derivative
**URL:** https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272
**Category:** General Usage
**Tags:** package
**Created:** [November 30, 2024, 4:06am UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272 "2024-11-30T04:06:20Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@hatmatrix](https://discourse.julialang.org/u/hatmatrix)
#### Post date: [November 30, 2024, 4:06am UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/1 "2024-11-30T04:06:20Z")
Following this example [here](https://discourse.julialang.org/t/generate-julia-expressions-with-symbolics/75528/3), I am trying to generate Julia or MATLAB code from a derivative.
```julia
using Symbolics
@variables x a b c
D = Differential(x)
F = a*x^3 + b*x^2 + c*x
dFdx = expand_derivatives(D(F))
```
Targeting Julia:
```julia
build_function(dFdx, x, a, b, c, target=Symbolics.JuliaTarget())
```
How do I convert the following expression to Julia syntax?
```julia
:(function (x, a, b, c)
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:385 =#
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:386 =#
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:387 =#
(+)((+)(c, (*)((*)(2, b), x)), (*)((*)(3, a), (^)(x, 2)))
```
I think MacroTools.jl might have something but have not found the appropriate function.
Targeting MATLAB:
```julia
build_function(dFdx, x, a, b, c, target=Symbolics.MATLABTarget())
```
For any symbolic expression, I get this type of error:
```julia
BoundsError: attempt to access 3-element Vector{Symbol} at index [4]
throw_boundserror(A::Vector{Symbol}, I::Tuple{Int64}) at essentials.jl:14
getindex at essentials.jl:916 [inlined]
numbered_expr(::SymbolicUtils.BasicSymbolic{Real}, ::Dict{Num, Tuple{Int64, Int64}}, ::Num, ::Vararg{Num}; varordering::Num, offset::Int64, states::SymbolicUtils.Code.LazyState, lhsname::Symbol, rhsnames::Vector{Symbol}) at build_function.jl:590
kwcall(::@NamedTuple{offset::Int64, lhsname::Symbol, rhsnames::Vector{Symbol}, varordering::Num}, ::typeof(Symbolics.numbered_expr), ::SymbolicUtils.BasicSymbolic{Real}, ::Dict{Num, Tuple{Int64, Int64}}, ::Num, ::Vararg{Num}) at build_function.jl:583
#462 at none:0 [inlined]
iterate(::Base.Generator{Vector{Any}, Symbolics.var"#462#465"{Num, Int64, Symbol, Vector{Symbol}, Dict{Num, Tuple{Int64, Int64}}}}) at generator.jl:48
numbered_expr(::SymbolicUtils.BasicSymbolic{Real}, ::Dict{Num, Tuple{Int64, Int64}}, ::Num, ::Vararg{Num}; varordering::Num, offset::Int64, states::SymbolicUtils.Code.LazyState, lhsname::Symbol, rhsnames::Vector{Symbol}) at build_function.jl:598
kwcall(::@NamedTuple{lhsname::Symbol, rhsnames::Vector{Symbol}, offset::Int64}, ::typeof(Symbolics.numbered_expr), ::SymbolicUtils.BasicSymbolic{Real}, ::Dict{Num, Tuple{Int64, Int64}}, ::Num, ::Vararg{Num}) at build_function.jl:583
_build_function(::Symbolics.MATLABTarget, ::Vector{Num}, ::Num, ::Vararg{Num}; columnmajor::Bool, conv::Function, expression::Type, fname::Symbol, lhsname::Symbol, rhsnames::Vector{Symbol}) at build_function.jl:995
_build_function(::Symbolics.MATLABTarget, ::Vector{Num}, ::Num, ::Num, ::Num, ::Num) at build_function.jl:969
_build_function(::Symbolics.MATLABTarget, ::Num, ::Num, ::Vararg{Num}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}) at build_function.jl:1011
_build_function(::Symbolics.MATLABTarget, ::Num, ::Num, ::Num, ::Num, ::Num) at build_function.jl:1011
build_function(::Num, ::Vararg{Num}; target::Symbolics.MATLABTarget, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}) at build_function.jl:87
kwcall(::@NamedTuple{target::Symbolics.MATLABTarget}, ::typeof(build_function), ::Num, ::Vararg{Num}) at build_function.jl:86
```
Any suggestions on how to proceed?
---
### Author:  [@Christin602Bey](https://discourse.julialang.org/u/Christin602Bey)
#### Post date: [November 30, 2024, 5:50am UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/2 "2024-11-30T05:50:57Z")
Hello!
I have the exact same problem. Have tried a variety of things. Me too facing the similar issues.
Best Regards,
Christin
---
### Author:  [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [November 30, 2024, 6:58am UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/3 "2024-11-30T06:58:52Z")
`build_function(..., expression=false)` causes it to return a function instead of an expression.
---
### Author:  [@gdalle](https://discourse.julialang.org/u/gdalle)
#### Post date: [November 30, 2024, 7:43am UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/4 "2024-11-30T07:43:51Z")
As @baggepinnen said, you can easily generate a Julia _function_ (object) from the derivative’s symbolic expression. In most cases, that should be sufficient, unless you really want to generate Julia _code_ (text)?
---
### Author:  [@hatmatrix](https://discourse.julialang.org/u/hatmatrix)
#### Post date: [November 30, 2024, 1:55pm UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/5 "2024-11-30T13:55:55Z")
Yes, actually I want to paste the code into MATLAB to work with some legacy code. If it doesn’t work with MATLABTarget I was content to manually edit the Julia code to make it MATLAB compatible.
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [November 30, 2024, 2:44pm UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/6 "2024-11-30T14:44:21Z")
The MATLAB target needs to be generalized to handle more general functions. It handles a lot of the ODE cases that come from MTK but not all sets of input arguments but it hasn’t been high on the priority list. It wouldn’t be so hard for someone who cares to edit it though.
>
---
### Author:  [@hatmatrix](https://discourse.julialang.org/u/hatmatrix)
#### Post date: [November 30, 2024, 2:53pm UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/7 "2024-11-30T14:53:47Z")
It seems to return something close to anonymous function syntax mixed with AST expressions.
```julia
RuntimeGeneratedFunction(#=in Symbolics=#, #=using Symbolics=#, :((x, a, b, c)->begin
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:385 =#
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:386 =#
#= /home/user/.julia/packages/SymbolicUtils/jf8aQ/src/code.jl:387 =#
(+)((+)(c, (*)((*)(2, b), x)), (*)((*)(3, a), (^)(x, 2)))
end))
```
To state my use case, I’m actually interested in generating Julia code so that I can copy-paste it into MATLAB (with some modifications).
I feel like the expression above should be convertible with a function like `ast.unparse` in Python but I cannot find the equivalent function in Julia.
---
### Author:  [@hatmatrix](https://discourse.julialang.org/u/hatmatrix)
#### Post date: [November 30, 2024, 2:55pm UTC](https://discourse.julialang.org/t/generate-code-from-symbolics-jl-derivative/123272/8 "2024-11-30T14:55:03Z")
I see - thanks. I am content to manually edit (with string replace) Julia code to MATLAB for the moment.