Changeset 96153e4 in sasmodels


Ignore:
Timestamp:
May 20, 2018 11:22:28 PM (3 months ago)
Author:
butler
Branches:
master, ESS_GUI, beta_approx, beta_approx_lazy_results, beta_approx_new_R_eff, doc_update, ticket-1104-resolution, ticket-1112, ticket-1142-plugin-reload, ticket-1148-Sq-scale-background, ticket-608-user-defined-weights
Children:
fc7bcd5
Parents:
c64a68e
Message:

more corrections and normalizations

Addreses #896. Brings parallelepiped and core-shell parallelepiped more
into line with each other and corrects angle definitions refering to
orietnational distribution docs for details. Still need to sort out
with Paul Kienzle the proper order the angles are applied.

Location:
sasmodels/models
Files:
2 edited

Legend:

Unmodified
Added
Removed
  • sasmodels/models/core_shell_parallelepiped.py

    r5bc6d21 r96153e4  
    44 
    55Calculates the form factor for a rectangular solid with a core-shell structure. 
    6 The thickness and the scattering length density of the shell or 
    7 "rim" can be different on each (pair) of faces. 
     6The thickness and the scattering length density of the shell or "rim" can be 
     7different on each (pair) of faces. The three dimensions of the core of the 
     8parallelepiped (strictly here a cuboid) may be given in *any* size order as 
     9long as the particles are randomly oriented (i.e. take on all possible 
     10orientations see notes on 2D below). To avoid multiple fit solutions, e 
     11specially with Monte-Carlo fit methods, it may be advisable to restrict their 
     12ranges. There may be a number of closely similar "best fits", so some trial and 
     13error, or fixing of some dimensions at expected values, may help. 
    814 
    915The form factor is normalized by the particle volume $V$ such that 
     
    1824pulled out of the form factor term due to the multiple slds in the model. 
    1925 
    20 The core of the solid is defined by the dimensions $A$, $B$, $C$ such that 
    21 $A < B < C$. 
     26The core of the solid is defined by the dimensions $A$, $B$, $C$ here shown 
     27such that $A < B < C$. 
    2228 
    2329.. figure:: img/parallelepiped_geometry.jpg 
     
    104110~~~~~~~~~~~~~ 
    105111 
    106 If the scale is set equal to the particle volume fraction, $\phi$, the returned 
    107 value is the scattered intensity per unit volume, $I(q) = \phi P(q)$. However, 
    108 **no interparticle interference effects are included in this calculation.** 
    109  
    110112There are many parameters in this model. Hold as many fixed as possible with 
    111113known values, or you will certainly end up at a solution that is unphysical. 
    112114 
    113 The returned value is in units of |cm^-1|, on absolute scale. 
    114115 
    115116NB: The 2nd virial coefficient of the core_shell_parallelepiped is calculated 
     
    120121 
    121122For 2d data the orientation of the particle is required, described using 
    122 angles $\theta$, $\phi$ and $\Psi$ as in the diagrams below. For further 
    123 details of the calculation and angular dispersions see :ref:`orientation`. 
    124 The angle $\Psi$ is the rotational angle around the *long_c* axis. For example, 
    125 $\Psi = 0$ when the *short_b* axis is parallel to the *x*-axis of the detector. 
     123angles $\theta$, $\phi$ and $\Psi$ as in the diagrams below, for further details 
     124of the calculation and angular dispersions see :ref:`orientation` . 
     125 
     126The angle $\Psi$ is the rotational angle around the $C$ axis. 
     127For $\theta = 0$ and $\phi = 0$, $\Psi = 0$ corresponds to the $B$ axis 
     128oriented parallel to the y-axis of the detector with $A$ along the x-axis. 
     129For other $\theta$, $\phi$ values, the parallelepiped has to be first rotated 
     130$\theta$ degrees in the $z-x$ plane and then $\phi$ degrees around the $z$ axis, 
     131before doing a final rotation of $\Psi$ degrees around the resulting $C$ axis 
     132of the particle to obtain the final orientation of the parallelepiped. 
    126133 
    127134.. note:: For 2d, constraints must be applied during fitting to ensure that the 
  • sasmodels/models/parallelepiped.py

    rb343226 r96153e4  
    1919 
    2020The three dimensions of the parallelepiped (strictly here a cuboid) may be 
    21 given in *any* size order. To avoid multiple fit solutions, especially 
    22 with Monte-Carlo fit methods, it may be advisable to restrict their ranges. 
    23 There may be a number of closely similar "best fits", so some trial and 
    24 error, or fixing of some dimensions at expected values, may help. 
     21given in *any* size order as long as the particles are randomly oriented (i.e. 
     22take on all possible orientations see notes on 2D below). To avoid multiple fit 
     23solutions, especially with Monte-Carlo fit methods, it may be advisable to 
     24restrict their ranges. There may be a number of closely similar "best fits", so 
     25some trial and error, or fixing of some dimensions at expected values, may 
     26help. 
    2527 
    2628The form factor is normalized by the particle volume and the 1D scattering 
     
    8082of the calculation and angular dispersions see :ref:`orientation` . 
    8183 
    82 .. Comment by Miguel Gonzalez: 
    83    The following text has been commented because I think there are two 
    84    mistakes. Psi is the rotational angle around C (but I cannot understand 
    85    what it means against the q plane) and psi=0 corresponds to a||x and b||y. 
    86  
    87    The angle $\Psi$ is the rotational angle around the $C$ axis against 
    88    the $q$ plane. For example, $\Psi = 0$ when the $B$ axis is parallel 
    89    to the $x$-axis of the detector. 
    90  
    9184The angle $\Psi$ is the rotational angle around the $C$ axis. 
    9285For $\theta = 0$ and $\phi = 0$, $\Psi = 0$ corresponds to the $B$ axis 
     
    9790of the particle to obtain the final orientation of the parallelepiped. 
    9891 
     92.. note:: For 2d, constraints must be applied during fitting to ensure that the 
     93   inequality $A < B < C$ is not violated, and hence the correct definition 
     94   of angles is preserved. The calculation will not report an error, 
     95   but the results may be not correct. 
     96    
    9997.. _parallelepiped-orientation: 
    10098 
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