| | 9 | * Propose that all form factor models have both "rescale" and "volfraction" as parameters, where rescale defaults to 1.0 (correct for neutron SANS data in absolute units). |
| | 10 | |
| | 11 | * We could have two versions of each S(Q), one as now, with radius_effective in S(Q) constrained to the geometric parameters in the form factor, and a second where a radius_effective parameter appears which can be separately adjusted - as most of us scientists would rather use this. |
| | 12 | |
| | 13 | Even better, with a single version of each S(Q), radius_effective could always appear, with a three state selector - fitting, fixed or constrained. |
| | 14 | |
| | 15 | * Such a three state selector would be useful to turn constraints on & off without having to edit the constraints tab. Note the current constraints were originally envisaged as operating between two FitPage tabs rather than within a single FitPage tab, which as a general feature would have consequences for polydispersity integrations. |
| | 16 | |
| | 17 | * Constraints within a single FitPage tab become particularly usful if there is a way to rapdily introduce an extra parameter. |
| | 18 | e.g. I want a new parameter R_ratio =(radius_core + thick_shell)/radius_core but don't want to write a re-parametrised model to fit, or more likely fix, the value of R_ratio. We may decide that in sasview the only good way to do this is actually to have to write a new model..... (sigh). |
| | 19 | |
| | 20 | * Introduce a system in the models to flag an issue if too many scale parameters being asked to adjust simultaneously. e.g. FitOneOf(rescale, volfraction, sld_core.AND.sld_shell.AND.sld_solvent ) This is not completely foolproof as it fails if say sld_shell = sld_solvent. In theory the least squares ought to be able to spot perfect correlations then complain also. |
| | 21 | |
