KNITRO.jl underwent a major rewrite between versions 0.12.0 and 0.13.0, with the low-level wrapper now being generated automatically with Clang.jl. Users of JuMP should see no breaking changes, but if you used the lower-level C API you will need to update your code accordingly.

KNITRO.jl

KNITRO.jl is a Julia interface to the Artelys Knitro solver.

It has two components:

Note: This wrapper is maintained by the JuMP community with help from Artelys. Please contact Artelys support if you encounter any problem with this interface or the solver.

Installation

First, purchase and install a copy of Knitro from Artelys.

Then, install KNITRO.jl using the Julia package manager:

import Pkg; Pkg.add("KNITRO")

KNITRO.jl is available free of charge and in no way replaces or alters any functionality of Artelys Knitro solver.

Troubleshooting

If you are having issues installing, here are several things to try:

  • Make sure that you have defined your global variables correctly, for example with export KNITRODIR="/path/to/knitro-vXXX-$OS-64" and export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$KNITRODIR/lib". You can check that KNITRO.jl sees your library with using KNITRO; KNITRO.has_knitro().

  • If KNITRO.has_knitro() returns false but you are confident that your paths are correct, try running build KNITRO and restarting Julia. In at least one user's experience, installing and using KNITRO in a temporary Julia environment (activated with ] activate --temp) does not work and the need to manually build is likely the reason why.

Use with JuMP

Use the KNITRO.Optimizer to use KNITRO with JuMP or MathOptInterface:

using JuMP
import KNITRO
model = Model(KNITRO.Optimizer)
set_optimizer_attribute(model, "honorbnds", 1)
set_optimizer_attribute(model, "outlev", 1)
set_optimizer_attribute(model, "algorithm", 4)

Use with AMPL

Pass KNITRO.amplexe to use KNITRO with the package AmplNLWriter.jl package:

using JuMP
import AmplNLWriter
import KNITRO
model = Model(() -> AmplNLWriter.Optimizer(KNITRO.amplexe, ["outlev=3"]))

Use with other packages

A variety of packages extend KNITRO.jl to support other optimization modeling systems. These include:

Low-level wrapper

KNITRO.jl implements most of Knitro's functionalities. If you aim at using part of Knitro's API that are not implemented in the MathOptInterface/JuMP ecosystem, you can refer to the low-level API, which wraps Knitro's C API (whose templates are specified in the file knitro.h).

Extensive examples using the C wrapper can be found in examples/.

Multithreading

Due to limitations in the interaction between Julia and C, KNITRO.jl disables multithreading if the problem is nonlinear. This will override any options such as par_numthreads that you may have set. Read GitHub issue #93 for more details.