# How to add user-defined nonlinear functions as constraints with JuMP?

**URL:** <https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436>\
**Category:** Optimization (Mathematical)\
**Tags:** jump\
**Created:** [June 5, 2018, 7:56am UTC](https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436 "2018-06-05T07:56:07Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![mrapo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mrapo/32/3911_2.png) [@mrapo](https://discourse.julialang.org/u/mrapo)\
**Post date:** [June 5, 2018, 7:56am UTC](https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436/1 "2018-06-05T07:56:07Z")

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Is it possible to add user-defined nonlinear functions as constraints in JuMP? I couldn’t find any documentation about a case like this nor any examples where someone would have done this.  
I mean something like this:

```
JuMP.register(m, :g, 1, g, autodiff=true)
JuMP.addNLconstraint(m, g(x) <= 0)

```

If this is not possible, then is there any way to do this kind of optimization with Julia?

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [June 5, 2018, 8:17am UTC](https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436/2 "2018-06-05T08:17:55Z")

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Have you tried? It should work exactly as you have 🙂 (Although you probably want to use `@NLconstraint` instead of `addNLconstraint`.)

The docs are being updated for the new version of JuMP, but I have opened an issue to make sure it gets addressed. [https://github.com/JuliaOpt/JuMP.jl/issues/1323](https://github.com/JuliaOpt/JuMP.jl/issues/1323)

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<div class="post-metadata">

**Author:** ![mrapo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mrapo/32/3911_2.png) [@mrapo](https://discourse.julialang.org/u/mrapo)\
**Post date:** [June 5, 2018, 10:31am UTC](https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436/3 "2018-06-05T10:31:10Z")

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Yes of course I’ve tried my example @odow , but it didn’t work, probably because my variable was a vector. However I now figured how it can be done:

```
f(x) = x[1]^2+2*x[2]+3
g(x) = x[1]^3+x[2]^2

JuMP.register(m, :f, 2, f, autodiff=true)
JuMP.register(m, :g, 2, g, autodiff=true)

JuMP.setNLobjective(m, :Min, :(f($(x...)))
JuMP.addNLconstraint(m, :(g($(x...))<=10))) # This line is the one I had trouble with

```

Interesting that similar examples really don’t exist anywhere in JuMP’s documentation.

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [June 5, 2018, 8:24pm UTC](https://discourse.julialang.org/t/how-to-add-user-defined-nonlinear-functions-as-constraints-with-jump/11436/4 "2018-06-05T20:24:37Z")

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> Yes of course I’ve tried my example

Oops, sorry for coming across as blunt, it wasn’t clear if it was a general question or whether there was a specific problem.

Glad you got it working. Another option is:

```julia
using JuMP, Ipopt

m=Model(solver=IpoptSolver())
@variable(m, x[1:2])

f(x...) = x[1]^2+2*x[2]+3
g(x...) = x[1]^3+x[2]^2

JuMP.register(m, :f, 2, f, autodiff=true)
JuMP.register(m, :g, 2, g, autodiff=true)

@NLobjective(m, Min, f(x[1], x[2]))
@NLconstraint(m, g(x[1], x[2]) <= 10)

solve(m)

```

> Interesting that similar examples really don’t exist anywhere in JuMP’s documentation.

Yes. Pull requests to improve the docs are always welcome 🙂