oj! Algorithms - ojAlgo - is Open Source Java code that has to do with mathematics, linear algebra and optimisation.
ojAlgo is available at The Central (Maven) Repository to be used with your favourite dependency management tool.
<dependency>
<groupId>org.ojalgo</groupId>
<artifactId>ojalgo</artifactId>
<version>43.0</version>
</dependency>...or download the jar from SourceForge.
General information about ojAlgo is available at the project web site: http://ojalgo.org/
User documentation wiki with examples is here at GitHub: https://github.com/optimatika/ojAlgo/wiki
Programming questions related to ojAlgo are best asked at stack overflow. Just remember to actually mention ojAlgo and tag the question using 'ojalgo' and whatever other tags you find suitable.
Bug reports and feature requests should preferably be posted here at GitHub: https://github.com/optimatika/ojAlgo/issues (Please do not use GitHub Issues for questions, discussions or support requests!)
The ojAlgo-user mailing list can be used for just about anything as long as it relates to ojAlgo. (Note that you have to be a member to post to that list!)
ojAlgo is Open Source, and you are strongly encouraged to clone or fork this repository and work directly with the source code. The source code is (part of) the documentation, and you should read it.
Feel free to contribute any way you want. Whatever you feel is missing or "wrong", just fix it.
One very good way to contribute is to supply test cases that verify that the functionality you use works as expected. The ojAlgo code base is often refactored. Having tests specific to your use case can be very beneficial (for you) in assuring future releases.
...or have a look at the list of open issues to see if there is something you can help out with.