Given an n x n integer matrix A whose eigenvalues are strictly greater than 1
in absolute value, let \sigma_A be the transformation of the n-torus
T^n=R^n/Z^n defined by \sigma_A(e^{2\pi ix})=e^{2\pi iAx} for x\in R^n. We
study the associated crossed-product C*-algebra, which is defined using a
certain transfer operator for \sigma_A, proving it to be simple and purely
infinite and computing its K-theory groups.