Hi, there are a couple of ways to do matrix vector and matrix matrix operations in the literature, most trade efficiency for complexity in implementation. We eventually plan to release a sub-library for this, but it won’t be available in the short term.
In response to the question of how to encrypt a matrix, I suggest looking at Matrix multiplication posted by a user to see how they implemented some basic matrix operations. It may not be the most efficient but you can use that as a starting point.
There is a very detailed example of an applicatoin that uses matrix arithmetic, but it is highly optimized for speed, and not in an easily digestable form (i.e. it is all inline code). It may be difficult to understand. It is based on a IDASH paper: https://eprint.iacr.org/2019/223.pdf . The code will make sense only after looking at the paper. GitHub - openfheorg/openfhe-genomic-examples
Hope this helps.