Fig. 5.

For the heterogeneous model example, consider the situation where tissue sample is made up two materials—1 and 2 with elastic parameters $(A_1,B_1)$ and $(A_2,B_2)$, respectively. ${\mathit{\tau }}_1\ne {\mathit{\tau }}_2$ is required to break the symmetry of the problem and make its Hessian non-singular everywhere