Improved asymmetric peak parameter refinement

New expressions for the calculation of axial asymmetry peak shape parameter derivatives in the Finger, Cox and Jephcoat model [J. Appl. Cryst. (1994), 27, 892–900] are presented. Code utilizing the new expressions shows an improved range of convergence for powder diffraction peak shape refinements, particularly when the parameters are transformed to A = H + S and B = H − S.