Hi, I have been programming a MILP for university. The model is feasible and was already solved using GLPK, CBC, Gurobi and CPLEX. The results are as expected and were carefully examined already. However, I have an issue solving the model using ECOS and Ipopt. Everytime, during the call in JuMP solve(myModel) I get the following errors, dependent on the solver I am trying to use:

```
LoadError: LoadError: MethodError: no method matching setvartype!
(::ECOS.ECOSMathProgModel, ::Array{Symbol,1})
```

or

```
LoadError: LoadError: MethodError: no method matching setvartype!
(::Ipopt.IpoptMathProgModel, ::Array{Symbol,1})
```

The source code, regarding the solvers is rather simple and looks like this:

```
using ECOS
myModel = Model(solver=ECOSSolver())
```

or

```
using Ipopt
myModel = Model(solver=IpoptSolver())
```

I am puzzled. I figured the problem might be related to the variables I am using, which look like this:

```
@variable(myModel, h[set_1] >= 0, Int);
@variable(myModel, i[set_1] >= 0, Int);
@variable(myModel, j[set_1] >= 0);
@variable(myModel, k[set_1] >= 0);
@variable(myModel, l[set_1] >= 1, Int);
@variable(myModel, m[set_1, set_2], Bin);
@variable(myModel, T >= 0, Int);
## FIX VARIABLES
#--------------------------------------------------------------------------
for(i,value) in enumerate(set_1)
if param_1[value] >= 0
JuMP.fix(h[value],param_1[value])
JuMP.fix(i[value],param_1[value]+param_2[value])
JuMP.fix(j[value],param_1[value])
JuMP.fix(k[value],param_1[value]+param_2[value])
JuMP.fix(l[value],1)
println(Symbol("Variables regarding ",value," fixed."))
end
end
```

Anyways, I hope somebody encountered the issue before. Maybe, that I don’t understand something that is fundamental. I am using the Atom editor. Thanks for your help.

**Problem solved!**

I had posted the question on Stackoverflow, as well.