Have you taken a look at this document called White Paper - Using PI Data with MATLAB ?
Matlab allows you to import .NET libraries and use it. Therefore, you can import PI AF SDK library and retrieve PI Data to the Matlab workspace. Another alternative is to use PI Web API which is also compatible with event-frames.
Please let me know if you have any questions,
The major use case for the Integrator for BA is to shaped the data into a format that's easily consumed by 3rd party analytic tools. Typically what this means is that the output of the Integrator is a simple two dimensional table. I would assume MATLAB has native capabilities to access simple tables? For example, does MATLAB provide native ODBC connectivity to an external database? If so, then you're set in terms of retrieving the Integrator shaped data.
If you want to write the results back to PI and you want to do so programmatically, then I would refer you to Marcos' post above.
As always there are a number of options to integrate Matlab with PI. We've used the AF SDK, which you will need to use as the PI SDK can't access EventFrames. I wrote a blog post a few years ago that will hopefully give you an idea of how to get started.
@Steve: Yes you can access an OLE-DB, ODBC or JDBC data source using Matlab if you have the Database Toolbox. The one limitation of the current integrators or OLE-DB is that you can't write back to AF, something that Jerry mentioned.