Similarly to the 'rafbas' utility, 'etprog' reads from the local file 'et_in' and writes to the local file 'et_tmp'. It also prints some output which gives information on what the meaning is of the numbers in the file 'et_in'. The result in 'et_tmp' is almost of the form (N-values basis, α-values basis, β-values basis, N-values fit, α-values fit, β-values fit).
The main task of etprog is to generate a fit set corresponding to the basis set information generated by rafbas. To this purpose, it first generates the most diffuse and most contracted products of basis functions. This defines the range which should at least be well described by the fit set. However, the range is extended somewhat more to further increase the quality of the fit. Experience shows that, at least for light elements, this indeed leads to very small fit errors in molecular calculations, at the expense of a large fit. The beta values for the fit are read from the input file and originate from a data statement in the rafbas program.