Opened 3 years ago

Last modified 12 months ago

#552 new enhancement

star_polymer model

Reported by: richardh Owned by: richardh
Priority: major Milestone: SasView 4.3.0
Component: SasView Keywords:
Cc: Work Package: SasView Bug Fixing

Description

numerically unstable at extreme small Q, likely also the same in mono_gauss_coil and poly_gauss_coil

suspect needs Taylor expansion

Change History (6)

comment:1 Changed 3 years ago by richardh

Also it is fitting <Rg2> not Rg, is this to be expected for this type of model?

Last edited 3 years ago by butler (previous) (diff)

comment:2 Changed 2 years ago by pkienzle

poly_gauss_coil has been fixed.

comment:3 Changed 2 years ago by pkienzle

Maybe use sinc() in lamellar.py.

Glatter(1982) gives:

    I(q) = 2 pi/q^2  drho^2 T^2 [sin(q T/2) / (q T/2)]^2

This doesn't help with the divergence at q=0 though.

Note that we have

    I(q) = 2 pi/q^2 drho^2 4 [sin(q T/2)]^2 / (q^2 T)

which differs by a factor of T.

Are we really sure that we want to return 1.0 as the form volume? Or do we not want to volume normalize by lamellae thicknesses when computing the polydispersity average?

comment:4 Changed 2 years ago by smk78

Did you really mean to add that last comment to this ticket, Paul? Those formulae don't look like a star polymer…

comment:5 Changed 17 months ago by richardh

The star_polymer calculation is rather noisy at very small Q when Rg is small and the number of arms is 2 or larger. This requires further investigation.

( A star_polymer_v2 is now in model marketplace, which fits Rg not Rg2, it also corrects isssue in the docs, for which see #962 )

Last edited 12 months ago by butler (previous) (diff)

comment:6 Changed 12 months ago by butler

  • Milestone changed from SasView Next Release +1 to SasView 4.3.0
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