I remember seeing a post on here where someone linked to the Matrix patent and the USPTO listed the patent as
"Patent Expired for Failure to Pay Maintenance Fees."
**EDIT found it**
Patent # is 5613483
Aplication # is 08555625 https://ramps.uspto.gov/eram/patentMaintFees.do
Enter the numbers and click bibliographic data
Not shure if this is the only Matrix patnet.