id summary reporter owner description type status priority milestone component resolution keywords cc workpackage 472 reparameterize Teubner-Strey pkienzle ajj "The current implementation of Teubner-Strey use parameters scale, c1, c2 and background. Since scale and background are automatic parameters in sasmodels, this was changed to a2, c1 and c2. Propose changing the parameters to the more physically meaningful repeat length d, correlation length xi and a scale factor. This will give more useful parameter uncertainties. A little bit of algebra gives a2/c2 and c1/c2 in terms of xi and d: a2/c2 = (xi^-2^ + (2 pi/d)^2^)^2^ c1/c2 = (xi^-2^ - (2 pi/d)^2^)^2^ The scale factor comes from the normalized form (Schubert, 1994): I(q) = (8 pi c2 eta^2^ / xi) / (a2 + c1 q^2^ + c2 q^4^) where eta^2^ = phi(1-phi)(delta rho)^2^ for volume fraction phi and scattering length density difference delta rho. The following parameters should be sufficient: sld, sld_solvent, phi in (0,1), xi > 0, and d > 0 using I(q) = (8 pi phi(1-phi)(delta rho)^2^) / ((1+(2 pi xi/d)^2^)^2^ + (1-(2 pi xi/d)^2^)^2^ q^2^ + q^4^) with two of phi, sld and sld_solvent fixed." enhancement closed critical SasView 4.0.0 SasView fixed SasModels Redesign