# JuMP 0.19 create constraints iteratively

**URL:** <https://discourse.julialang.org/t/jump-0-19-create-constraints-iteratively/25525>\
**Category:** General Usage\
**Tags:** jump\
**Created:** [June 21, 2019, 1:14pm UTC](https://discourse.julialang.org/t/jump-0-19-create-constraints-iteratively/25525 "2019-06-21T13:14:24Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![plapplop](https://avatars.discourse-cdn.com/v4/letter/p/bbce88/32.png) [@plapplop](https://discourse.julialang.org/u/plapplop)\
**Post date:** [June 21, 2019, 1:14pm UTC](https://discourse.julialang.org/t/jump-0-19-create-constraints-iteratively/25525/1 "2019-06-21T13:14:24Z")

</div>

I’m new to JuMP and I’m trying to model a simple problem:

```julia
using JuMP, Gurobi

months = 1:12
n_months = length(months)
demands = [30, 15, 15, 25, 33, 40, 45, 45, 26, 14, 25, 30]
cap = 20

model = Model(with_optimizer(Gurobi.Optimizer))
@variable(model, 0 <= pnorm[1:n_months] <= cap, Int)
@variable(model, 0 <= pover[1:n_months] <= 0.5 * cap, Int)
@variable(model, 0 <= store[1:n_months], Int)

@constraint(model,
            con_balance,
            pnorm[1:n_months] + pover[1:n_months] + store[1:n_months]
                .== demands[1:n_months] + store[1:n_months])

```

except that the constraint for the first month `t = 1` is different, so it should be something like:

```julia
istock = 2
@constraint(model,
            con_balance[1:1],
            pnorm[1:1] + pover[1:1] + istock
                .== demands[1:1] + store[1:1])

```

So I tried defining the constraints iteratively by using `@constraintref` (as mentioned here: [Expressions and Constraints — JuMP -- Julia for Mathematical Programming 0.13 documentation](http://www.juliaopt.org/JuMP.jl/v0.13/refexpr.html#constraint-references), last block of code) and looping over the elements of the constraint array but it seems to belong to older version of JuMP only and is not available in 0.19 anymore. I can’t find the equivalent now… does anybody know how I should handle that?

Many thanks!

---

<div class="post-metadata">

**Author:** ![miles.lubin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/miles.lubin/32/279_2.png) [@miles.lubin](https://discourse.julialang.org/u/miles.lubin)\
**Post date:** [June 22, 2019, 3:53pm UTC](https://discourse.julialang.org/t/jump-0-19-create-constraints-iteratively/25525/2 "2019-06-22T15:53:42Z")

</div>

There are a few ways to do this. Here’s one:

```julia
con_balance = Dict()
con_balance[1] = @constraint(model, pnorm[1] + pover[1] + istock == demands[i] + store[i])
for i in 2:N
    con_balance[i] = @constraint(model, pnorm[i] + pover[i] == demands[i] + store[i])
end

```

If you don’t need to keep the reference to the constraint (e.g., to modify coefficients later), you can write:

```julia
@constraint(model, pnorm[1] + pover[1] + istock == demands[i] + store[i])
for i in 2:N
    @constraint(model, pnorm[i] + pover[i] == demands[i] + store[i])
end

```

---

<div class="post-metadata">

**Author:** ![plapplop](https://avatars.discourse-cdn.com/v4/letter/p/bbce88/32.png) [@plapplop](https://discourse.julialang.org/u/plapplop)\
**Post date:** [June 23, 2019, 10:18am UTC](https://discourse.julialang.org/t/jump-0-19-create-constraints-iteratively/25525/3 "2019-06-23T10:18:36Z")

</div>

Wonderful, thanks, the `Dict` one is exactly what I needed, sorry if I overlooked it in the doc (I tried…).