  In this paper, we prove new results on the validity of the limiting amplitude
principle (LAP) for the wave equation with nonconstant coefficients, not
necessarily in divergence form. Under suitable assumptions on the coefficients
and on the source term, we establish the LAP for space dimensions 2 and 3. This
result is extended to one space dimension with an appropriate modification. We
also quantify the LAP and thus provide estimates for the convergence of the
time-domain solution to the frequency-domain solution. Our proofs are based on
time-decay results of solutions of some auxiliary problems. The obtained
results are illustrated numerically on radially symmetric problems in
dimensions 1, 2 and 3.
