Opened 6 years ago

Closed 6 years ago

#1018 closed enhancement (fixed)

add Boltzmann distribution

Reported by: dirk Owned by: dirk
Priority: major Milestone: SasView 4.2.0
Component: sasmodels Keywords:
Cc: Work Package: SasModels New Model


To describe the orientation behaviour of magnetic particles with moment mu (in terms of Bohr magneton muB) in a magnetic field of strength mu0 H (in T), usually the Boltzmann propability distribution P(x)=L exp(L x)/exp(-L)/exp(2L-1) is used. Here x=Cos(theta), where theta is the angle between the magnetic easy axis of the magnetic moment with respect to the magnetic field direction. The so-called Langevin factor L= mu0 H mu muB/kb T.

Change History (6)

comment:1 Changed 6 years ago by dirk

To make it similiar with the other Sasview distribution, the plan is now to parametrise the Boltzmann like P(x) = exp( -|x - c|/sigma) where sigma=k T/E is the inverse Boltzmann factor. So for an aligning system at high field with large Zeeman energy, i.e. Em>k T, sigma will tend 0, as it is usually defined.

comment:2 Changed 6 years ago by dirk

In a5a12caaceba1c450d16a4bf8a7fc30ceab60a04/sasmodels:

implementation of Boltzmann distribution refs #1018

comment:3 Changed 6 years ago by dirk

  • Resolution set to worksforme
  • Status changed from new to closed

comment:4 Changed 6 years ago by richardh

  • Milestone changed from sasmodels WishList to SasView 4.2.0
  • Priority changed from minor to major
  • Resolution worksforme deleted
  • Status changed from closed to reopened

Why is the  sasmodels branch - "Boltzmann" - associated with this ticket still not pulled?

I think that this branch also has a "uniform" distribution as well as the rectangular one, see #764


comment:5 Changed 6 years ago by richardh

in sasmodels branch Boltzmann if I save project then load it again, a “uniform” distribution fails to load back in, gives error messages

2018-01-16 17:24:50 : Error: This model state has missing or outdated information.

Traceback (most recent call last):

File "C:\sasview42\sasview\src\sas\sasgui\perspectives\fitting\", line 2036, in reset_page


File "C:\sasview42\sasview\src\sas\sasgui\perspectives\fitting\", line 1283, in reset_page_helper


File "C:\sasview42\sasview\src\sas\sasgui\perspectives\fitting\", line 1375, in _reset_page_disp_helper


KeyError: 'theta.width'

2018-01-16 17:24:50 : Completed loading.

The Boltzmann distribution seems to work OK, so looks like it is Paul K’s recent (good) idea to do away with Nsigs for the Uniform distribution is upsetting the loader.

comment:6 Changed 6 years ago by butler

  • Resolution set to fixed
  • Status changed from reopened to closed

This change was merged a while back but apparently the ticket was not closed. Doing so now.

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