An object of name x is already attached to this model. If this is intended, consider using the anonymous construction syntax

Specific Domains Optimization (Mathematical)
1

I am using Ipopt to solve the non linear optimization problem. My code is running but gives an error when the final solution is to be dispalyed as " An object of name x is already attached to this model. If this is intended, consider using the anonymous construction syntax. " How do I solve this please?

My code is below

using JuMP
import Juniper
import Ipopt
 NumVar = 5
    a = [46.891299081399524, 18.358839924481327, 24.81156595151281, 14.307918586681046, 45.809245326064875] # x-cordinates of selected circle
    b = [34.20824038054229, 34.209275827684294, 15.03051769314379, 5.0321444549166845, 17.229495614433407] # y-cordinates of selected circle
    r = [20, 20, 20, 20, 20 ] # Radius of selected circles
    R = 0.0
model = Model(
        optimizer_with_attributes(
            Juniper.Optimizer,
            "nl_solver" => optimizer_with_attributes(
                Ipopt.Optimizer, 
                MOI.Silent() => true,
            ),
        ),
    )


function inner_loop(x, y,R)


    for i in 1:length(a)
        R = max(R, sqrt((a[i] - x)^2 + (b[i] - y)^2) + r[i])
    end
    #model = Model(Mosek.Optimizer)
    @variable(model, x >= 0)
    @variable(model, y >= 0)
    @variable(model, z >= 0)
  
    @NLobjective(model, Min, x^2 + y^2 - z)
    @NLconstraint(
        model, 
        [i in 1:NumVar],
        -2 * x * a[i] - 2 * b[i] * y + z <= (R - r[i])^2 - a[i]^2 - b[i]^2, )
  
    @show model
print(model)
    optimize!(model)

    return value(x), value(y), value(z), value(R)
end

function main()
    x, y, z, R = 0.0, 0.0, Inf, 0.0
    while abs(x^2 + y^2 - z) >= 0.01
        x, y, z, R = inner_loop(x, y,R,)
    end
    
    print("The abs value is: abs(x^2+y^2-z) = " , abs(x^2+y^2-z))
    
    return x, y, z, R
end

main()
2

You construct a single model outside the function, and then inside the function, this line is commented out. So it’s trying to build add variables to the existing problem, instead of constructing a new one. Just move your current model definition inside the inner_loop function.

3

If I move the model definition inside the inner loop it keeps running and printing just the model continuously without giving the final solution. What will have caused this please?

4

Because your solution never satisfies your termination condition for the loop.

I suggest you take another look at the formulation, on paper, and think about your objective.