Changeset eda8b30 in sasmodels for sasmodels/models/cylinder.py

Timestamp:

Oct 28, 2017 6:42:15 AM (6 years ago)

Author:

richardh

Branches:

master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests

Children:

5f8b72b

Parents:

da5536f

Message:

further changes to model docs for orientation calcs

File:

• sasmodels/models/cylinder.py (modified) (3 diffs)

sasmodels/models/cylinder.py

@@ -54 +54 @@
 when $P(q) \cdot S(q)$ is applied.
 
-For oriented cylinders, we define the direction of the
+For 2d scattering from oriented cylinders, we define the direction of the
 axis of the cylinder using two angles $\theta$ (note this is not the
 same as the scattering angle used in q) and $\phi$. Those angles
-are defined in :numref:`cylinder-angle-definition` .
+are defined in :numref:`cylinder-angle-definition` , for further details see :ref:`orientation` .
 
 .. _cylinder-angle-definition:
@@ -63 +63 @@
 .. figure:: img/cylinder_angle_definition.png
 
-    Definition of the $\theta$ and $\phi$ orientation angles for a cylinder relative
-    to the beam line coordinates, plus an indication of their orientation distributions
-    which are described as rotations about each of the perpendicular axes $\delta_1$ and $\delta_2$
+    Angles $\theta$ and $\phi$ orient the cylinder relative
+    to the beam line coordinates, where the beam is along the $z$ axis. Rotation $\theta$, initially 
+    in the $xz$ plane, is carried out first, then rotation $\phi$ about the $z$ axis. Orientation distributions
+    are described as rotations about two perpendicular axes $\delta_1$ and $\delta_2$
     in the frame of the cylinder itself, which when $\theta = \phi = 0$ are parallel to the $Y$ and $X$ axes.
 
@@ -73 +74 @@
 
 The $\theta$ and $\phi$ parameters to orient the cylinder only appear in the model when fitting 2d data.
-On introducing "Orientational Distribution" in the angles, "distribution of theta" and "distribution of phi" parameters will
-appear. These are actually rotations about the axes $\delta_1$ and $\delta_2$ of the cylinder, which when $\theta = \phi = 0$ are parallel
-to the $Y$ and $X$ axes of the instrument respectively. Some experimentation may be required to understand the 2d patterns fully.
-(Earlier implementations had numerical integration issues in some circumstances when orientation distributions passed through 90 degrees, such
-situations, with very broad distributions, should still be approached with care.)
 
 Validation