  We test the predictive power of first-oder reversal curve (FORC) diagrams
using simulations of random magnets. In particular, we compute a histogram of
the switching fields of the underlying microscopic switching units along the
major hysteresis loop, and compare to the corresponding FORC diagram. We find
qualitative agreement between the switching-field histogram and the FORC
diagram, yet differences are noticeable. We discuss possible sources for these
differences and present results for frustrated systems where the discrepancies
are more pronounced.
