Trace Sudoku

The trace of a two-by-two matrix is simply the sum of the top left entry and bottom right entry.  There are many reasons why people would want to consider this, even in a first course in linear algebra.  Lately I'm more interested in the fact that trace alone can be used to construct sudoku with unique solutions.  No cells need to be revealed: the trace of matrices in each three by three square is enough to completely determine the answer.

For a sample, here is a one way that this three by three square with trace clues can be filled out.

Here is a full sudoku with a unique solution determined only by the trace of its two-by-two matrices.

Link to higher quality PDF for printing.