Hello,

I’m trying to optimize a simple normal linear model likelihood function and have two questions. The code I am using is below:

```
using Optim
nobs = 500
nvar = 1
β = ones(nvar)*3.0
x = [ones(nobs) randn(nobs,nvar-1)]
ε = randn(nobs)*0.5
y = x*β + ε
function LL_anon(X, Y, β, σ)
-(-length(X)*log(2π)/2 - length(X)*log(σ) - (sum((Y - X*β).^2) / (2σ^2)))
end
LL_anon(X,Y, pars) = LL_anon(X,Y, pars...)
res2 = optimize(vars -> LL_anon(x,y, vars...), [1.0,1.0]) # Start values: β=1.0, σ=1.0
```

This actually works and I get the following:

```
* Algorithm: Nelder-Mead
* Starting Point: [1.0,1.0]
* Minimizer: [2.980587812647935,0.5108406803949835]
* Minimum: 3.736217e+02
* Iterations: 47
* Convergence: true
* √(Σ(yᵢ-ȳ)²)/n < 1.0e-08: true
* Reached Maximum Number of Iterations: false
* Objective Calls: 92
```

My questions are as follows:

- My initial example has only an intercept and sigma and when I try and add another X variable, I get an error message and I’m not sure why?

```
MethodError: no method matching LL_anon(::Array{Float64,2}, ::Array{Float64,1}, ::Float64, ::Float64, ::Float64)
Closest candidates are:
LL_anon(::Any, ::Any, ::Any, ::Any) at In[297]:2
LL_anon(::Array{Float64,1}, ::Array{Float64,1}, ::Any, ::Any) at In[113]:2
LL_anon(::Any, ::Any, ::Any) at In[297]:4
...
Stacktrace:
[1] (::##245#246)(::Array{Float64,1}) at .\In[299]:1
[2] value!!(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\NLSolversBase\src\interface.jl:9
[3] initial_state(::Optim.NelderMead{Optim.AffineSimplexer,Optim.AdaptiveParameters}, ::Optim.Options{Float64,Void}, ::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/solvers/zeroth_order\nelder_mead.jl:136
[4] optimize(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}, ::Optim.NelderMead{Optim.AffineSimplexer,Optim.AdaptiveParameters}, ::Optim.Options{Float64,Void}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\optimize.jl:25
[5] #optimize#151(::Array{Any,1}, ::Function, ::Tuple{##245#246}, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:62
[6] #optimize#148(::Array{Any,1}, ::Function, ::Function, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:52
[7] optimize(::Function, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:52
```

- If I change the start value in my original working example to [2.0,2.0] I get the following error message:

```
log will only return a complex result if called with a complex argument. Try log(complex(x)).
Stacktrace:
[1] nan_dom_err at .\math.jl:300 [inlined]
[2] log at .\math.jl:419 [inlined]
[3] LL_anon(::Array{Float64,2}, ::Array{Float64,1}, ::Float64, ::Float64) at .\In[302]:2
[4] (::##251#252)(::Array{Float64,1}) at .\In[304]:1
[5] value(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\NLSolversBase\src\interface.jl:19
[6] update_state!(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Optim.NelderMeadState{Array{Float64,1},Float64,Array{Float64,1}}, ::Optim.NelderMead{Optim.AffineSimplexer,Optim.AdaptiveParameters}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/solvers/zeroth_order\nelder_mead.jl:193
[7] optimize(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}, ::Optim.NelderMead{Optim.AffineSimplexer,Optim.AdaptiveParameters}, ::Optim.Options{Float64,Void}, ::Optim.NelderMeadState{Array{Float64,1},Float64,Array{Float64,1}}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\optimize.jl:51
[8] optimize(::NLSolversBase.NonDifferentiable{Float64,Array{Float64,1},Val{false}}, ::Array{Float64,1}, ::Optim.NelderMead{Optim.AffineSimplexer,Optim.AdaptiveParameters}, ::Optim.Options{Float64,Void}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\optimize.jl:25
[9] #optimize#151(::Array{Any,1}, ::Function, ::Tuple{##251#252}, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:62
[10] #optimize#148(::Array{Any,1}, ::Function, ::Function, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:52
[11] optimize(::Function, ::Array{Float64,1}) at C:\Users\dolacomb\.julia\v0.6\Optim\src\multivariate/optimize\interface.jl:52
```

Again, I’m not sure why this is happening and since start values are very important I’d like to know how to overcome this issue.

I’d like to attach the .ipynb file but cannot do so.

Any help would be greatly appreciated.