```
a = [1, 2, 3, 4]
sum(a[n] for n in 1:0) # ERROR: MethodError: reducing over an empty collection is not allowed; consider supplying `init` to the reducer
using JuMP
m = Model()
@constraint(m, sum(a[n] for n in 1:0) >= 0) # It's OK.
```

Correct. In normal Julia you need to pass the `init`

keyword:

```
julia> a = [1, 2, 3, 4]
4-element Vector{Int64}:
1
2
3
4
julia> sum(a[n] for n in 1:0; init = 0)
0
```

We have this set by default in JuMP because we know that people really want `0.0`

when they have an empty summation.

4 Likes

Thanks! Nice setting!

1 Like