1. Add new source to your Installer.app

iMatrix application is in the STE Package and you can find iMatrix application inside Productivity catalog in Installer application.
Also, you can install it from project's repository if you like to get most update version fastest way.
Launch Installer on your iPhone and go to Sources. Press Edit button and then Add.
Add new source:http://www.iMatrix.LT/repo/repository.plist
Press Done button and refresh sources. You have to find new repository in the list: OSG Repository

2. Install iMatrix

Then, staying in Installer, go to Install tab and find 2D code section. Select it.
Select iMatrix aplication from the list.
Install iMatrix.
Leave Installer.

Find iMatrix on desktop

After successful installation you should find iMatrix on your Summer Board