# Optim: Problems with Fminbox and the NelderMead algorithm

Hi,

Today my Optim package was updated. However, after this update, the optimization doesn’t work anymore. For the optimization I use the Nelder-Mead algorithm. In order to set some boundaries, I use Fminbox, i.e., the optimization call looks like this:

res = optimize(x → calc_mse( x ), lower, upper, x0, Fminbox(NelderMead()) )

Whereas the code was running fine before the update, now he did not find a minimum, and furthermore two issues occur:
i) the resulting value of objective function is larger than the initial one, and
ii) (at least) one component of the fitting parameter exceeds the boundaries.

An example which reproduces my problem is the following (using Julia 1.5.2):

using Optim

function calc_mse(p)
x = p
y = p
return 1 ./ (abs.(sin.(x).^70 .* cos.(y)).^60 .+.01 )
end

offset = rand(2) / 10
x0 = [pi/2, pi] .+ offset
lower = [x0 - 0.1, x0 - 0.1]
upper = [x0 + 0.1, x0 + 0.1]
iterationen = 100
res0 = optimize(x → calc_mse( x ), x0, NelderMead(), Optim.Options(iterations = iterationen, show_trace = true, show_every=1) )
res1 = optimize(x → calc_mse( x ), lower, upper, x0, Fminbox(LBFGS()), Optim.Options(iterations = iterationen, show_trace = true, show_every=1) )
res2 = optimize(x → calc_mse( x ), lower, upper, x0, Fminbox(NelderMead()), Optim.Options(iterations = iterationen, show_trace = true, show_every=1) )

The unconstrained version of the Nelder-Mead algorithm works well. The same is true for the optimization with boundaries using the L-BFGS algorithm. Only the last one, which uses the Nelder-Mead algorithm, does not work.

Is this a bug or does something changed and have to be considered in the new version of Optim for the Nelder-Mead algorithm?

1 Like

What is `import Pkg; Pkg.status()`?

Pkg.status() gives:

Atom v0.12.30
BenchmarkTools v0.7.0
BlackBoxOptim v0.5.0
Images v0.24.1
Juno v0.8.4
LineSearches v7.1.1
Optim v1.3.0
Plots v1.14.0
PolynomialRoots v1.0.0
PyPlot v2.9.0
SpecialFunctions v0.10.3
StaticArrays v1.1.3

it seems that is a known error. but there isnt any hints on how to find the error

ah, ok. Thanks, I didn’t saw that this issue was already mentioned.