Fundamental WDF Elements

1. From the previous discussion, a WDF mass element has $R_0 = m$ and a digitized reflectance given by
   $$S_m(z) = -z^{-1}.$$

2. In a similar way, the discrete-time reflectance for a WDF spring with $R_0 = k$ is found to be
   $$S_k(z) = z^{-1}.$$

3. A WDF dashpot (or resistance) is defined to have $R_0 = \mu$ and a reflectance
   $$S_{\mu}(z) = 0.$$