# Option and Option Files on Octeract Engine

Octeract Engine allows users to customise their solving by changing solver options according to their preference. Let’s take a look at what exactly is meant by solver options and how to change these options using an options file.

Octeract Engine accepts custom options through a plain text file. The user can create an empty text file in the format octeract.opt. Within this file the options can be specified, as explained in the section below.

## Setting Custom Options in an Option File

It’s important to note that all options are case-sensitive. Each option requires a new line and they are set using the following syntax:

OPTION_NAME = option_value

To show this better, here’s an example.

Let’s assume that the user wants to:

• turn off the optimisation based bounds tightening technique (OBBT, default behaviour is on)
• set infinity to $$10^6$$ (default is $$10^7$$)
• adjust the convergence tolerance to 0.1 (default is $$10^{-3}$$ ) and
• allow Octeract Engine to run for 60 seconds (default is $$2\times10^9$$ seconds)
The contents of the options file should look like the text below:

            
#my octeract custom option file example
USE_OBBT = false
INFINITY = 1.e6
CONVERGENCE_TOLERANCE = 0.1
MAX_SOLVER_TIME = 60



For further information on how to change specific options, have a look at the Knowledge Base on the left sidebar.

## Using Custom Option Files in Third Party Software

When a *third party software is used, in conjunction with Octeract Engine, the user should follow the steps below:

• Create a text file with the name octeract.opt and save it in the location where the third party software will be run. The name should be exact and in lower case.
• Define custom options within octeract.opt.
A quick note on using a set of options defined, in the options file octeract.opt, when there is a change in location of the file being run.

If the user would like to use octeract.opt for a file in a different location (to where the options file is currently located), the options file octeract.opt will need to be added to this location.

For example, if a user chooses to run e.g. a Pyomo file by launching Pyomo at location/some/path/in/the/users/computer/ and this location includes an Octeract Engine options file octeract.opt. Octeract Engine will read octeract.opt automatically.

If the user wants to launch Pyomo for, the same or a different file at locationa/different/path/in/the/users/computer/ using the same set of options as before, the octeract.opt file needs to be copied from location /some/path/in/the/users/computer/ to a/different/path/in/the/users/computer/.

Therefore, the directory from which the third party software is launched is the correct location of the octeract.opt file.

*Third party software that Octeract Engine supports: Pyomo, Python, AMPL, GAMS, JuMP and C++.

## Using Custom Option Files from Terminal

For Octeract Engine usage, via a Terminal environment on Ubuntu/Linux/Unix or Command Prompt (CMD) on Windows, the user can choose how to use custom option files from the two methods mentioned below:

Method 1: the user can specify the custom options within a standard octeract.opt file in the directory where Octeract Engine will be run from.

Method 2: the user can append the following to the usual Octeract Engine call:

-o /path/to/options/file/octeract.opt