Hey everyone. I’m trying to figure out how to use JuMP to optimize a function of a slice of data over the left and right endpoints for the range.

I’ve never used JuMP before so I’m piecing this together from tutorials and the docs.

```
# data
x = randn(100)
# func to optimize
mysum(left, right, x = x) = sum(x[left:right])
m = Model()
@variable(m, left, lower_bound = 1, upper_bound = length(x))
@variable(m, right, lower_bound = 1, upper_bound = length(x))
@constraint(m, left + 20 <= right)
@constraint(m, left in MOI.Integer())
@constraint(m, right in MOI.Integer())
@objective(m, Max, mysum(left, right))
```

I get `ERROR: MethodError: no method matching isless(::GenericAffExpr{Float64,VariableRef}, ::GenericAffExpr{Float64,VariableRef})`

What am I doing wrong? What’s the correct way to specify this type of optimization problem?

Appreciate the help!

P.S. I tried rewriting

```
function mysum(left, right, x)
x_sub = [el for (i,el) in enumerate(x) if left ≤ i ≤ right]
sum(x_sub)
end
```

but it yields the same error.