# Fminbox and linesearch issues for box constrained optimization

**URL:** <https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273>\
**Category:** Optimization (Mathematical)\
**Created:** [November 7, 2018, 7:41pm UTC](https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273 "2018-11-07T19:41:58Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![axelle](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/axelle/32/4488_2.png) [@axelle](https://discourse.julialang.org/u/axelle)\
**Post date:** [November 7, 2018, 7:41pm UTC](https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273/1 "2018-11-07T19:41:58Z")

</div>

Good afternoon,

I cannot figure out the right syntax for a box constrained optimization but where i need to change the line search as I was getting an error: `ArgumentError: Value and slope at step length = 0 must be finite.` when using `res= optimize(bk, lower, upper, x0, Fminbox(inner_optimizer))` in the code below. because of this initial error, i tried to change the line search and tried out many different syntaxes, but I am always getting a method error.

I tried for example: `res= optimize(bk, x0, lower, upper, Fminbox(), optimizer = GradientDescent, linesearch=LineSearches.Static)` , or `res= optimize(bk, lower, upper, x0, Fminbox(GradientDescent()), linesearch=LineSearches.Static)`

Would anyone know the correct syntax or know how to solve the initial error if changing the line search is not the right path?

Many thanks!

Here is the full (initial) code:

```julia
using Optim
using QuadGK
using QuantEcon
using Interpolations
using LineSearches

module Para 
    Re=1.3
    Rl=1.1
    E=2.0
    points=3
    lowerB=0.01
end

    import ..Para

function solve(Gamma::AbstractFloat)
    
    u(c) = (c).^Gamma
    
    function bk_obj(Sb::AbstractFloat, 
                    c_bar::AbstractFloat,
                    D::AbstractFloat)

        Lf= Para.Rl/(Para.Re- Para.Rl) * D * c_bar
        Sf= Para.E - D - Lf
        
        if centralized
                P_star= (Lf /1 - Sb)
            else 
                P_star= Para.Re / Para.Rl
        end

        θhigh = (Para.Re * (1 - Sb) + Para.Re * (1 - Sb) * (P_star) - c_bar * (P_star) * D) / (c_bar * D * (Para.Re - (Lf / Sb)) )

        c1_ND = D * c_bar
        c1_D = (1 - Sb) + Lf
        c2ND(θ) = (((1 - Sb) - θ* c_bar * D) * Para.Rl + Sb * Para.Re + Lf * Para.Rl + Sf * Para.Re ) / (1 - θ)
        c2D(θ) = (1 - Sb) + Lf + ( (Sb + Sf) * Para.Re ) / (1 - θ)

        val1(θ) = u(θ * c1_ND + (1 - θ)* c2ND(θ)) 
        val2(θ) = u(θ * c1_D + (1 - θ)* c2D(θ)) 

        return -(quadgk(val1, 0.1, θhigh)[1] + quadgk(val2, θhigh, 0.999)[1])

    end 

        grid = collect(range(Para.lowerB, length=Para.points, stop=Para.E))
        inner_optimizer = GradientDescent()

        for (i,D) in enumerate(grid)

            bk(x) = bk_obj(x[1], x[2], D)
            D_vec[i]= D
            lower = [0.05, 0.1]
            upper = [D, D]
            x0 = [0.05, 0.1]
       
          res= optimize(bk, lower, upper, x0, Fminbox(inner_optimizer))
        end
    
end

solve(2.3)

```

and the initial error that made me try change the line search:

```julia
ArgumentError: Value and slope at step length = 0 must be finite.

Stacktrace:
 [1] macro expansion at C:\Users\arquie\.julia\packages\Parameters\35RKe\src\Parameters.jl:734 [inlined]
 [2] (::HagerZhang{Float64,Base.RefValue{Bool}})(::getfield(LineSearches, Symbol("#ϕ#1")){Optim.ManifoldObjective{OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}},Array{Float64,1},Array{Float64,1},Array{Float64,1}}, ::getfield(LineSearches, Symbol("#ϕdϕ#6")){Optim.ManifoldObjective{OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}},Array{Float64,1},Array{Float64,1},Array{Float64,1}}, ::Float64, ::Float64, ::Float64) at C:\Users\arquie\.julia\packages\LineSearches\SrdrY\src\hagerzhang.jl:111
 [3] HagerZhang at C:\Users\arquie\.julia\packages\LineSearches\SrdrY\src\hagerzhang.jl:101 [inlined]
 [4] perform_linesearch!(::Optim.GradientDescentState{Array{Float64,1},Float64}, ::GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Optim.InverseDiagonal,getfield(Optim, Symbol("##56#62")){Array{Float64,1},Array{Float64,1},Fminbox{GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Nothing,getfield(Optim, Symbol("##12#14"))},Float64,getfield(Optim, Symbol("##46#48"))}}}, ::Optim.ManifoldObjective{OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}}) at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\utilities\perform_linesearch.jl:40
 [5] update_state!(::OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}, ::Optim.GradientDescentState{Array{Float64,1},Float64}, ::GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Optim.InverseDiagonal,getfield(Optim, Symbol("##56#62")){Array{Float64,1},Array{Float64,1},Fminbox{GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Nothing,getfield(Optim, Symbol("##12#14"))},Float64,getfield(Optim, Symbol("##46#48"))}}}) at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\solvers\first_order\gradient_descent.jl:74
 [6] optimize(::OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}, ::Array{Float64,1}, ::GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Optim.InverseDiagonal,getfield(Optim, Symbol("##56#62")){Array{Float64,1},Array{Float64,1},Fminbox{GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Nothing,getfield(Optim, Symbol("##12#14"))},Float64,getfield(Optim, Symbol("##46#48"))}}}, ::Optim.Options{Float64,Nothing}, ::Optim.GradientDescentState{Array{Float64,1},Float64}) at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\optimize\optimize.jl:57
 [7] optimize at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\optimize\optimize.jl:33 [inlined]
 [8] optimize(::OnceDifferentiable{Float64,Array{Float64,1},Array{Float64,1}}, ::Array{Float64,1}, ::Array{Float64,1}, ::Array{Float64,1}, ::Fminbox{GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Nothing,getfield(Optim, Symbol("##12#14"))},Float64,getfield(Optim, Symbol("##46#48"))}, ::Optim.Options{Float64,Nothing}) at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\solvers\constrained\fminbox.jl:229
 [9] #optimize#53(::Bool, ::Symbol, ::Function, ::Function, ::Array{Float64,1}, ::Array{Float64,1}, ::Array{Float64,1}, ::Fminbox{GradientDescent{InitialPrevious{Float64},HagerZhang{Float64,Base.RefValue{Bool}},Nothing,getfield(Optim, Symbol("##12#14"))},Float64,getfield(Optim, Symbol("##46#48"))}, ::Optim.Options{Float64,Nothing}) at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\solvers\constrained\fminbox.jl:164
 [10] optimize at C:\Users\arquie\.julia\packages\Optim\wi7Vp\src\multivariate\solvers\constrained\fminbox.jl:163 [inlined] (repeats 2 times)
 [11] solve(::Float64, ::Bool) at .\In[19]:66
 [12] solve(::Float64) at .\In[19]:19
 [13] top-level scope at In[20]:1

```

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<div class="post-metadata">

**Author:** ![mohamed82008](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mohamed82008/32/18171_2.png) [@mohamed82008](https://discourse.julialang.org/u/mohamed82008)\
**Post date:** [November 8, 2018, 12:52am UTC](https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273/2 "2018-11-08T00:52:33Z")

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```julia
suboptimizer = GradientDescent(linesearch=LineSearches.Static())
res = optimize(bk, lower, upper, x0, Fminbox(suboptimizer))

```

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<div class="post-metadata">

**Author:** ![axelle](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/axelle/32/4488_2.png) [@axelle](https://discourse.julialang.org/u/axelle)\
**Post date:** [November 8, 2018, 11:07am UTC](https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273/3 "2018-11-08T11:07:12Z")

</div>

thanks so much!!

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<div class="post-metadata">

**Author:** ![pkofod](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pkofod/32/2179_2.png) [@pkofod](https://discourse.julialang.org/u/pkofod)\
**Post date:** [November 8, 2018, 11:41am UTC](https://discourse.julialang.org/t/fminbox-and-linesearch-issues-for-box-constrained-optimization/17273/4 "2018-11-08T11:41:18Z")

</div>

Let me just note that this is also asked (or a variant of it at least) here [Syntax combining Fminbox and LineSearch · Issue #688 · JuliaNLSolvers/Optim.jl · GitHub](https://github.com/JuliaNLSolvers/Optim.jl/issues/688)