# Xpress NonLinear

**URL:** https://discourse.julialang.org/t/xpress-nonlinear/74669
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [January 15, 2022, 2:18pm UTC](https://discourse.julialang.org/t/xpress-nonlinear/74669 "2022-01-15T14:18:35Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![andreab](https://avatars.discourse-cdn.com/v4/letter/a/4af34b/32.png) [@andreab](https://discourse.julialang.org/u/andreab)
#### Post date: [January 15, 2022, 2:18pm UTC](https://discourse.julialang.org/t/xpress-nonlinear/74669/1 "2022-01-15T14:18:35Z")

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Is there a package in the JuMP ecosystem providing an interface to FICO Xpress NonLinear solver?

Xpress.jl seems to support only Xpress Optimizer.  
If I try to use Xpress.jl to solve a non-convex NLP, I get the following error:  
“ERROR: LoadError: The solver does not support nonlinear problems (i.e., NLobjective and NLconstraint)”.

I tried also to use AmplNLWriter

```julia
model = Model(() -> AmplNLWriter.Optimizer("amplxpress"))

```

but it seems that amplxpress only supports Xpress Optimizer  
“XPRESS 39.01.01: Sorry, XPRESS 39.01.01 cannot handle a non-quadratic nonlinear objective”

The same problem is solved correctly when feeding the corresponding .nl file to Xpress Console Optimizer, so the issue is not in the solver.

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<div class="post-metadata">

### Author: ![bbrunaud](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bbrunaud/32/1737_2.png) [@bbrunaud](https://discourse.julialang.org/u/bbrunaud)
#### Post date: [February 19, 2022, 3:33am UTC](https://discourse.julialang.org/t/xpress-nonlinear/74669/2 "2022-02-19T03:33:50Z")

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Xpress does not solve non linear models. FICO Xpress NonLinear is actually the solver Knitro.