Inverse Volume Inequalities for Matrix Weights

For weights in the matricial Muckenhoupt classes we investigate a number of properties analogous to properties which hold in the scalar Muckenhoupt classes. In contrast to the scalar case we exhibit for eachp ,1 <p<1, a matrix weight W 2Ap;qn S p0<pAp0;q0. We also give a necessary and suYcient condition on W inAp;q, a "reverse inverse volume inequality", to ensure thatW is inAp0;q0 for somep 0 <p .