Expressions for first and second derivatives in least-squares refinements including extinction

Compact expressions are given for first and second derivatives necessary for inclusion of the Becker-Coppens isotropic extinction model in a least-squares procedure. Derivatives with respect to a scale factor, a structural parameter, and the two extinction parameters g and ρ are considered, for refinements on vertical strokeFvertical stroke and vertical strokeFvertical stroke2. (orig.)