I am reading the performance tips of JuMP. It says “The most important rule is to avoid global variables”, but I am not sure what it means in the JuMP context and how to implement it.

In the example below, the value of X, Z, K, L are known and defined before JuMP. They are needed to calculate the objective function of the optimization problem. How should I avoid having them as global variables?

```
using JuMP, Ipopt
m = Model(Ipopt.Optimizer)
@variable(m, θ[1:4])
@variable(m, δ[1:H])
# X, Z, K, L are known data
mu = @expression(m, X * reshape(θ, (K, L)) * Z')
v = @expression(m, δ .+ mu)
# more arguments..
```