Dear Karina, I think that the answer for sasview 4.2.2 is "local monodisperse", the same S(Q) is used for all radii in a polydisperse form factor. The default addition of an S(Q) ties the radius used in the S(Q) to the mean radius from the P(Q). Creating a P(Q)S(Q) product in the "plugin model" editor instead allows a different "effective radius" in the S(Q) to that from the P(Q)
From sasview 4.3 we started to add some further functionality, which is now even further improved in sasview 5 where an option to include the beta(Q) decoupling approximation is introduced. This damps out oscillations due to S(Q) to allow at least approximately for the effects of polydispersity and/or non-spherical particle shapes. Sasview 5 also allows, where appropriate, for different choices of which radius to use in the S(Q), for example for a cylinder, the half length, the radius or the diagonal radius.
For greater detail I would recommend downloading sasview 5 and reading the improved documentation in that version. Regards Richard Heenan From: users [mailto:users-bounces@lists.sasview.org] On Behalf Of Abitaev, Karina via users Sent: 07 April 2020 10:04 To: users@sasview.org Subject: [SasView Users] Sum Multi Function Version 4.2.2 Dear Sasview Team, I am using Sasview 4.2.2 to fit a colloidal crystal of polymer nanoparticles. Here I use a Form factor for spheres, where a polydispersity is included. Furthermore, I am using a hard sphere structure factor. I found the option to multiply the Spheres with hard spheres, so I can supply for each a radius and polydispersity. In this context I was wondering how the structure factor and form factor are combined (decoupling approximation, local monodisperse approx, ...) Thank you in advance for your help! Best wishes, Karina -- Karina Abitaev Institut für Physikalische Chemie Universität Stuttgart Pfaffenwaldring 55 70569 Stuttgart Germany karina.abitaev@ipc.uni-stuttgart.de Phone: +49 (0)711/685-64502 Fax: +49 (0)711/685-64443