Provide model for the Pringle-Schmidt helical form factor

[smk78]

Request from Ian Hamley (i.w.hamley@…):

Would be possible to incorporate the Pringle-Schmidt helical form factor into SasView? It is used in quite a few studies now. There are other helical form factors (see attached) but the Pringle-Schmidt form factor is more generally and more widely used.

I don’t have code although I know some people who might – Heinz Amenitsch or Pierre Terech. These two groups also have data and fits in their papers.

I have datasets waiting to be fitted, as does Daniel Hermida-Merino at the ESRF.

[smk78]

Original Pringle-Schmidt paper (1971)

[smk78]

Hamley Overview of Helical Ribbon form factors

[smk78]

Teixeira form factor of Helical Tape

[butler]

Given the existence of the marketplace as a distribution mechanism and the impact to 4.1 this could easily be moved to 4.2 and should not impact the release of 4.1. Will leave here for now as work is ongoing and depending on when the freeze is this could make it in.

[smk78]

Tim has coded a model and uploaded it to the Marketplace. (But has been unable to upload an example dataset because of Ticket #685)

Ian has been told the model is available and has been given instruction on how to implement and use it. We await feedback from him!

If/when the model is given the thumbs up it should be added to the sasmodels library.

[tim]

I have now heard from Ian and he is using the model with some of his data. Presuming that this returns a sane result then this ticket can be closed.

[butler]

This is available in the marketplace and at any rate in no way a blocker for this release.Given the imminent freeze for a 4.1 release am going ahead and moving this to 4.2.