ADAPTFEKO is the adaptive frequency utility used to automatically select smaller frequency steps near narrow resonances and larger steps where the results are relatively smooth.

For each frequency, ADAPTFEKO creates a .pre file and calls PREFEKO and the Solver. The file names are derived from the original name plus _fr_n_ada_m where n and m are incremental numerical values (for example, the new files associated with test.pre are test_fr1_ada_1.pre, test_fr1_ada_2.pre, ...).