# How to write a constraint in JuMP where the index has if-else structure
**URL:** https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [March 8, 2019, 2:27pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635 "2019-03-08T14:27:11Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@angeloaliano1](https://discourse.julialang.org/u/angeloaliano1)
#### Post date: [March 8, 2019, 2:27pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635/1 "2019-03-08T14:27:11Z")
I have a little question in how to write a constraint in Jump language. The constraint is:
sum\_{i} sum\_{r=0}^{9} x[i,j,t-r] \<= 1, for all t=1,…,12 and j=1,…,9
if t - r \< 0, change by t - r + 9.
How can I use a if-else structure inside a sum() to incorporate the condition above?
Thanks!
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### Author:  [@Rajat\_Sanyal](https://discourse.julialang.org/u/Rajat_Sanyal)
#### Post date: [March 8, 2019, 3:07pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635/2 "2019-03-08T15:07:06Z")
Could you explain a bit more? What is the range of i? Note that there is a term t-r=0 which is basically the zeroth index of the variable. Julia array starts from 1, so that would be an error.
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### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [March 8, 2019, 3:15pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635/3 "2019-03-08T15:15:04Z")
Option 1: use Julia’s inplace `cond ? true : false` syntax
```julia
for t in 1:12, j in 1:9
@constraint(model, sum(x[i, j, t-r < 0 ? t-r : t-r+9] i in 1:N, r in 0:9) <= 1)
end
```
Option 2: make a list of the third indices (can be much more general)
```julia
for t in 1:12, j in 1:9
third_index =Int[]
for r in 0:9
if t - r < 0
push!(third_index, t - r + 9)
else
push!(third_index, t - r)
end
end
@constraint(model, sum(x[i, j, k] i in 1:N, k in third_index) <= 1)
end
```
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### Author:  [@angeloaliano1](https://discourse.julialang.org/u/angeloaliano1)
#### Post date: [March 8, 2019, 3:35pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635/4 "2019-03-08T15:35:35Z")
Thank you for your response.
The range of i is i=1,…,30.
The constraint is given by:
sum\_{i=1}^{30} sum\_{r = 0}^{9} x[i,j,t-r] \<=1 for all j=1,…,9 and t= 1,…,12.
But, in my model, if t - r \<=0, then chance the term t-r by t - r + 12.
Did you understand my problem?
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### Author:  [@angeloaliano1](https://discourse.julialang.org/u/angeloaliano1)
#### Post date: [March 8, 2019, 3:42pm UTC](https://discourse.julialang.org/t/how-to-write-a-constraint-in-jump-where-the-index-has-if-else-structure/21635/5 "2019-03-08T15:42:20Z")
Wonderfull!
You solved my problem!!!
Best regards.