multilayer vesicle doesn't define effective radius

[pkienzle]

Documentation for multilayer vesicle says that it uses the outer shell radius as the effective radius when P(Q)*S(Q) is applied, but ER() is not defined, so no structure factor can be applied.

This feature was available in the MultiShellModel in 3.1.2.

Note that the equation docs can be improved for this model.

Also, it should use n_shells rather than n_pairs since there is one fewer solvent layer than shell layer.

[pkienzle]

Sasview 3.1.2 supports polydispersity on thickness of shell and solvent interlayers plus core, but 4.0.1 does not.

[pkienzle]

Pull request awaiting approval by someone who cares to check it.

The following shows that it is consistent with 4.0.1:

python ../../sasmodels/sascomp multilayer_vesicle,multilayer_vesicle.py -random n_pairs="int(n_shells+0.5)" -pars

Run this from sasmodels-master/sasmodels/models, where sasmodels-master/ is a separate clone of the git repo for sasmodels, and sasmodels/ is on the ticket-853 branch.

If you are on a unix-like operating system, you can make a symlink to sascomp and save a few keystrokes:

ln -s ~/src/sasmodels/sascomp ~/bin
sascomp multilayer_vesicle,multilayer_vesicle.py ...

[butler]

Actually, this is called a "vesicle" model. Thus "pairs" refers to the pairs of lipid monolayers required to make a single "bilayer" shell. That said the model is valid for any solid shells (whether from a bilayer or something else) so shells works as a name as well. Documentation will need to be very clear however about what is meant — in particular since this will be used almost exclusively by membrane people it should be clear that one shell = 1 bilayer = 2 layers of lipids.