Good hidden P-matrix sandwiches

We introduce two new classes of matrices that contain the class of P-matrices and can be recognized in polynomial time. These classes are related to the known classes of Hidden Minkowski and hidden positive row diagonally dominant matrices, which are subclasses of the P-matrix class. We show that for 3 × 3 matrices, the class of hidden prdd matrices coincides with the class of P-matrices. Alternative theorems for these hidden matrix classes are given and it is shown how one can use them to efficiently check membership in the classes.