are involved so that there will in general be insufficient information contained in the $S$-matrix elements for a single energy to yield a detailed and precise potential. The situation is even worse in cases where parity dependence must be assumed since this halves the information available for potential components of each parity. The problem can be ameliorated if $S$ is available for more than one energy. If $S$ is available over a narrow range of energies, then the algorithm can be made to yield to an energy independent potential; this is what we have earlier called ‘mixed case’ inversion (see Refs. [@ketal1; @zuev] and first of Ref. [@candm]) and, in effect, the information from the energy derivative of $S$ is exploited. In many cases, $S_{lj}$ or $S^J_{l'l}$ are provided over a wide range of energies. In this case one should ideally consider the potential to be energy dependent and determine the energy dependence itself. This can be done within the framework of the parameterisations presented above.

An example of where the sets of $S_{lj}$ or $S^J_{l'l}$ are too small to define the potential very closely is the $S\rightarrow V$ inversion situation embedded in the analysis of low energy, experimentally determined, 