Our implementation is using synonymous names for parameters compared to the paper by J.A. Wollmershauser, B. Clausen, and S.R. Agnew.
'xi_inf' and 'chi_inf' are not strictly "asymptotic values", but stresses that correspond to the back-extrapolation from the terminal linear hardening stage (characterized by 'h_inf_xi/chi').
All parameters are referenced back to their counterparts in the paper by J.A. Wollmershauser, B. Clausen, and S.R. Agnew.
Philip Eisenlohr