  We consider the inverse problem of the simultaneous identification of the
coefficients $\sigma$ and $q$ of the equation div$(\sigma\nabla u) + qu=0$ from
the knowledge of the complete Cauchy data pairs. We assume that $\sigma=\gamma
A$ where $A$ is a given matrix function and $\gamma, q$ are unknown piecewise
affine scalar functions. No sign, nor spectrum condition on $q$ is assumed. We
derive a result of global Lipschitz stability in dimension $n\geq 3$. The proof
relies on the method of singular solutions and on the quantitative estimates of
unique continuation.
