It depends on your definition of a test matrix, one description says a test matrix is used to track a series of test cases that are essentially the same. In this case the matrix compares specific functionality to the tests which cover it. But a test matrix could also be requirements to tests.
The actual coverage matrix is implied in TD. As a report can be generated indicating the requirement coverage, but personally I would like to see an actual matrix. I just haven't found one yet. I suppose that with thousands of test and hundreds of requirements, the matrix would be unmanageable anyway and completely impractical.