# How to use named parameters in objective function in Optimization.jl?

**URL:** <https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360>\
**Category:** Optimization (Mathematical)\
**Created:** [December 31, 2022, 3:15pm UTC](https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360 "2022-12-31T15:15:07Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![ForceBru](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/forcebru/32/21389_2.png) [@ForceBru](https://discourse.julialang.org/u/ForceBru)\
**Post date:** [December 31, 2022, 3:15pm UTC](https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360/1 "2022-12-31T15:15:07Z")

</div>

I’d like to refer to my design variables (parameters) by name inside my objective function, like this:

```julia
objective(params, data::AbstractVector) =
    sum(@. (params.a * data + params.b)^2)

```

What’s the recommended way of doing this?

* * *

I tried ComponentArrays and Optimization.jl:

```julia
import Optimization, Ipopt
using OptimizationMOI, ComponentArrays

objective(params::ComponentVector, data::AbstractVector) = sum(@. (params.a * data + params.b)^2)
data = randn(1000)

# julia> objective(ComponentVector(a=0.2, b=0.1), data)
# 52.10612648965923

prob = Optimization.OptimizationProblem(objective, ComponentVector(a=0.2, b=0.1), data)
# OptimizationProblem. In-place: true
# u0: ComponentVector{Float64}(a = 0.2, b = 0.1)

```

Now I try to optimize this:

> **Code with Optimization.jl and ComponentArrays**
>
> ```julia
> julia> Optimization.solve(prob, Ipopt.Optimizer())
> 
> ******************************************************************************
> This program contains Ipopt, a library for large-scale nonlinear optimization.
> Ipopt is released as open source code under the Eclipse Public License (EPL).
> For more information visit https://github.com/coin-or/Ipopt
> ******************************************************************************
> 
> This is Ipopt version 3.14.4, running with linear solver MUMPS 5.4.1.
> 
> Number of nonzeros in equality constraint Jacobian...: 0
> Number of nonzeros in inequality constraint Jacobian.: 0
> Number of nonzeros in Lagrangian Hessian.............: 3
> 
> ERROR: MethodError: objects of type Nothing are not callable
> Stacktrace:
> [1] eval_objective_gradient(moiproblem::OptimizationMOI.MOIOptimizationProblem{Float64, OptimizationFunction{true, SciMLBase.NoAD, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Matrix{Float64}, Matrix{Float64}, Matrix{Float64}}, G::Vector{Float64}, x::Vector{Float64})
> @ OptimizationMOI ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:87
> [2] eval_objective_gradient(model::Ipopt.Optimizer, grad::Vector{Float64}, x::Vector{Float64})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:525
> [3] (::Ipopt.var"#eval_grad_f_cb#2"{Ipopt.Optimizer})(x::Vector{Float64}, grad_f::Vector{Float64})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:598
> [4] _Eval_Grad_F_CB(n::Int32, x_ptr::Ptr{Float64}, #unused#::Int32, grad_f::Ptr{Float64}, user_data::Ptr{Nothing})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/C_wrapper.jl:54
> [5] IpoptSolve(prob::Ipopt.IpoptProblem)
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/C_wrapper.jl:442
> [6] optimize!(model::Ipopt.Optimizer)
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:727
> [7] __solve(prob::OptimizationProblem{true, OptimizationFunction{true, SciMLBase.NoAD, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}}, opt::Ipopt.Optimizer; maxiters::Nothing, maxtime::Nothing, abstol::Nothing, reltol::Nothing, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
> @ OptimizationMOI ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:329
> [8] __solve
> @ ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:276 [inlined]
> [9] #solve#540
> @ ~/.julia/packages/SciMLBase/QqtZA/src/solve.jl:84 [inlined]
> [10] solve(::OptimizationProblem{true, OptimizationFunction{true, SciMLBase.NoAD, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}}, ::Ipopt.Optimizer)
> @ SciMLBase ~/.julia/packages/SciMLBase/QqtZA/src/solve.jl:78
> [11] top-level scope
> @ REPL[10]:1
> 
> julia>
> 
> ```

It fails saying “MethodError: objects of type Nothing are not callable”, but I have no idea what it tried to call…

Anyway, let’s enable autodiff:

> **Same code, but with ForwardDiff (long error message!)**
>
> ```julia
> julia> prob = Optimization.OptimizationProblem(Optimization.OptimizationFunction(objective, Optimization.AutoForwardDiff()), ComponentVector(a=0.2, b=0.1), data)
> OptimizationProblem. In-place: true
> u0: ComponentVector{Float64}(a = 0.2, b = 0.1)
> 
> julia> Optimization.solve(prob, Ipopt.Optimizer())
> This is Ipopt version 3.14.4, running with linear solver MUMPS 5.4.1.
> 
> Number of nonzeros in equality constraint Jacobian...: 0
> Number of nonzeros in inequality constraint Jacobian.: 0
> Number of nonzeros in Lagrangian Hessian.............: 3
> 
> Total number of variables............................: 2
> variables with only lower bounds: 0
> variables with lower and upper bounds: 0
> variables with only upper bounds: 0
> Total number of equality constraints.................: 0
> Total number of inequality constraints...............: 0
> inequality constraints with only lower bounds: 0
> inequality constraints with lower and upper bounds: 0
> inequality constraints with only upper bounds: 0
> 
> ERROR: MethodError: no method matching objective(::Vector{Float64}, ::Vector{Float64})
> 
> Closest candidates are:
> objective(::ComponentVector, ::AbstractVector)
> @ Main REPL[6]:1
> 
> Stacktrace:
> [1] (::OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Optimization.var"#57#74"{ForwardDiff.GradientConfig{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}}, Tuple{Axis{(a = 1, b = 2)}}}}, Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}}, Optimization.var"#60#77"{ForwardDiff.HessianConfig{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, 2}}, Tuple{Axis{(a = 1, b = 2)}}}, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}}, Tuple{Axis{(a = 1, b = 2)}}}}, Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}}, Optimization.var"#63#80", Nothing, Optimization.var"#67#84"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Optimization.var"#72#89"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing})(::Vector{Float64}, ::Vararg{Vector{Float64}})
> @ SciMLBase ~/.julia/packages/SciMLBase/QqtZA/src/scimlfunctions.jl:3580
> [2] eval_objective(moiproblem::OptimizationMOI.MOIOptimizationProblem{Float64, OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Optimization.var"#57#74"{ForwardDiff.GradientConfig{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}}, Tuple{Axis{(a = 1, b = 2)}}}}, Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}}, Optimization.var"#60#77"{ForwardDiff.HessianConfig{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, 2}}, Tuple{Axis{(a = 1, b = 2)}}}, ComponentVector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Float64}, Float64, 2}}, Tuple{Axis{(a = 1, b = 2)}}}}, Optimization.var"#56#73"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}}, Optimization.var"#63#80", Nothing, Optimization.var"#67#84"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Optimization.var"#72#89"{OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Matrix{Float64}, Matrix{Float64}, Matrix{Float64}}, x::Vector{Float64})
> @ OptimizationMOI ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:78
> [3] eval_objective(model::Ipopt.Optimizer, x::Vector{Float64})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:514
> [4] (::Ipopt.var"#eval_f_cb#1"{Ipopt.Optimizer})(x::Vector{Float64})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:597
> [5] _Eval_F_CB(n::Int32, x_ptr::Ptr{Float64}, x_new::Int32, obj_value::Ptr{Float64}, user_data::Ptr{Nothing})
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/C_wrapper.jl:38
> [6] IpoptSolve(prob::Ipopt.IpoptProblem)
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/C_wrapper.jl:442
> [7] optimize!(model::Ipopt.Optimizer)
> @ Ipopt ~/.julia/packages/Ipopt/rQctM/src/MOI_wrapper.jl:727
> [8] __solve(prob::OptimizationProblem{true, OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}}, opt::Ipopt.Optimizer; maxiters::Nothing, maxtime::Nothing, abstol::Nothing, reltol::Nothing, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
> @ OptimizationMOI ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:329
> [9] __solve
> @ ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:276 [inlined]
> [10] #solve#540
> @ ~/.julia/packages/SciMLBase/QqtZA/src/solve.jl:84 [inlined]
> [11] solve(::OptimizationProblem{true, OptimizationFunction{true, Optimization.AutoForwardDiff{nothing}, typeof(objective), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, ComponentVector{Float64, Vector{Float64}, Tuple{Axis{(a = 1, b = 2)}}}, Vector{Float64}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}}, ::Ipopt.Optimizer)
> @ SciMLBase ~/.julia/packages/SciMLBase/QqtZA/src/solve.jl:78
> [12] top-level scope
> @ REPL[14]:1
> 
> julia>
> 
> ```

Now the error is:

```
no method matching objective(::Vector{Float64}, ::Vector{Float64})

```

Well, yes, that’s the point: I _don’t_ want the first argument to be a simple vector. I want something _vector-like_ that lets me refer to its elements by name, like a `ComponentVector`.

However, `ComponentVector`s don’t seem to work here because the optimization routine needs a plain `Vector`…

I can easily circumvent this by using a wrapper function whose first argument is a vector. It then creates a `ComponentVector` and calls the original objective function:

```julia
objective(params::Vector, data) =
    objective(ComponentVector(a=params[1], b=params[2]), data)

```

Then `Optimization.solve(prob, Ipopt.Optimizer())` works completely fine.

But this is exactly what I’m trying to avoid: I _don’t_ want to wrap each of my objective functions like this. I’ve been doing this for far too long and am now getting a little frustrated. It’s just boilerplate code and doesn’t get me much closer to solving the actual optimization problem.

* * *

What’s the recommended way of **accessing design variables by name** inside my objective functions?

---

<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:** [December 31, 2022, 3:16pm UTC](https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360/2 "2022-12-31T15:16:49Z")

</div>

> [@ForceBru](#):
>
> saying “MethodError: objects of type Nothing are not callable”, but I have no idea wha

Open an issue. The issue is that some of the optimizers (MOI here) are not robust to it, so we should create a test that loops through all of them and fix it one by one. I think MOI might be the only one (since it’s the one that doesn’t work by wrapping like this, and instead exposes the parameters to the lower level).

---

<div class="post-metadata">

**Author:** ![ForceBru](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/forcebru/32/21389_2.png) [@ForceBru](https://discourse.julialang.org/u/ForceBru)\
**Post date:** [December 31, 2022, 3:43pm UTC](https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360/3 "2022-12-31T15:43:10Z")

</div>

Done: [`MethodError: objects of type Nothing are not callable` when optimizing basic function with `OptimizationMOI` and Ipopt · Issue #448 · SciML/Optimization.jl · GitHub](https://github.com/SciML/Optimization.jl/issues/448). However, this only happens when I don’t use autodiff (so finite differences are used, I presume). When I enable autodiff, basic optimization (with a vector of parameters) works fine.  
The main question was how to properly refer to my parameters by name. Thanks for replying literally on New Year’s eve, by the way, I really appreciate it!

---

<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:** [December 31, 2022, 3:58pm UTC](https://discourse.julialang.org/t/how-to-use-named-parameters-in-objective-function-in-optimization-jl/92360/4 "2022-12-31T15:58:44Z")

</div>

```julia
ERROR: MethodError: objects of type Nothing are not callable
Stacktrace:
  [1] eval_objective_gradient(moiproblem::OptimizationMOI.MOIOptimizationProblem{Float64, OptimizationFunction{true, SciMLBase.NoAD, typeof(objective_basic), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing}, Vector{Float64}, Vector{Float64}, Matrix{Float64}, Matrix{Float64}, Matrix{Float64}}, G::Vector{Float64}, x::Vector{Float64})
    @ OptimizationMOI ~/.julia/packages/OptimizationMOI/ZoxrV/src/OptimizationMOI.jl:87

```

oh that’s because IPOPT requires a gradient. We should make that throw a better error earlier.