I’ll illustrate the problem with the following simple example:

```
import JuMP
l = ones(4)
model= JuMP.Model()
JuMP.@variable(model, x)
JuMP.@variable(model, y1)
JuMP.@variable(model, y2)
epxr = [
JuMP.@expression(model, y1 - 1),
JuMP.@expression(model, y2 - 2)]
```

In my objective function I want to have the scalar product of `l`

and `expr`

.

This does not work:

```
JuMP.@objective(model, Min, x * 3 + l[2:3]' * epxr))
```

MethodError: no method matching add_to_expression!(::GenericAffExpr{Float64,VariableRef}, ::Adjoint{Float64,Array{Float64,1}}, ::Array{GenericAffExpr{Float64,VariableRef},1})

FYI: If you would remove the term `x * 3`

it would work.

This does work:

```
JuMP.@objective(model, Min, x * 3 + sum(l[2:3] .* epxr))
```

This does too:

```
exp2 = l[2:3]' * epxr
JuMP.@objective(model, Min, x * 3 + exp2)
```

Why?