Fit, summarize and plot sinusoidal hysteretic processes using:
two-step simple harmonic least squares, ellipse-specific non-linear least
squares, the direct method, geometric least squares or linear least squares. See
Yang, F and A. Parkhurst, "Efficient Estimation of Elliptical Hysteresis with
Application to the Characterization of Heat Stress"
R Package for Modeling Rate-Dependent Hysteretic Processes and Ellipses.