# Equivalent-Circuit Fitting

Equivalent-circuit fitting of electrochemical impedance spectra has depended on a human choosing a circuit topology and starting values, even though different topologies can produce nearly identical spectra. A University of Zagreb team expanded a few manually fitted spectra into a synthetic reference library, projected it into principal-component space, and used nearest-neighbour retrieval to shortlist topologies and supply physically plausible starting values at once, then refined each candidate by complex nonlinear least squares and chose by fit quality. Against independent manual fits, most parameters agreed within 1%, reduced chi-squared was lower in every case, and one spectrum took about 5 to 6 seconds.

Equivalent-circuit fitting of electrochemical impedance spectra has depended on a human choosing a circuit topology and starting values, even though different topologies can produce nearly identical spectra. A University of Zagreb team expanded a few manually fitted spectra into a synthetic reference library, projected it into principal-component space, and used nearest-neighbour retrieval to shortlist topologies and supply physically plausible starting values at once, then refined each candidate by complex nonlinear least squares and chose by fit quality. Against independent manual fits, most parameters agreed within 1%, reduced chi-squared was lower in every case, and one spectrum took about 5 to 6 seconds.