Reverse the problem to spatial superposition where pressure response p_m(t) in some well m is decomposed into a sum of individual pressure responses from :
| p_m(t) = p_i + \sum_k \delta p_{km}(t, {\bf r}) = p_i + \sum_k \int_0^t p_{ukm}(t-\tau, {\bf r}) \, dq(\tau) |