Changes in sasmodels/models/cylinder.py [3330bb4:9802ab3] in sasmodels

File:

• sasmodels/models/cylinder.py (modified) (4 diffs)

sasmodels/models/cylinder.py

@@ -38 +38 @@
 
 
-Numerical integration is simplified by a change of variable to $u = cos(\alpha)$ with 
-$sin(\alpha)=\sqrt{1-u^2}$. 
+Numerical integration is simplified by a change of variable to $u = cos(\alpha)$ with
+$sin(\alpha)=\sqrt{1-u^2}$.
 
 The output of the 1D scattering intensity function for randomly oriented
@@ -61 +61 @@
 .. _cylinder-angle-definition:
 
-.. figure:: img/cylinder_angle_definition.jpg
+.. figure:: img/cylinder_angle_definition.png
 
-    Definition of the angles for oriented cylinders.
+    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 $\delta_2$ 
+    in the frame of the cylinder itself, which when $\theta = \phi = 0$ are parallel to the $Y$ and $X$ axes.
 
-The $\theta$ and $\phi$ parameters only appear in the model when fitting 2d data.
+.. figure:: img/cylinder_angle_projection.png
+
+    Examples for oriented cylinders.
+
+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
@@ -123 +135 @@
               ["length", "Ang", 400, [0, inf], "volume",
                "Cylinder length"],
-              ["theta", "degrees", 60, [-inf, inf], "orientation",
-               "latitude"],
-              ["phi", "degrees", 60, [-inf, inf], "orientation",
-               "longitude"],
+              ["theta", "degrees", 60, [-360, 360], "orientation",
+               "cylinder axis to beam angle"],
+              ["phi", "degrees",   60, [-360, 360], "orientation",
+               "rotation about beam"],
              ]
 
@@ -152 +164 @@
 tests = [[{}, 0.2, 0.042761386790780453],
         [{}, [0.2], [0.042761386790780453]],
-#  new coords    
+#  new coords
         [{'theta':80.1534480601659, 'phi':10.1510817110481}, (qx, qy), 0.03514647218513852],
         [{'theta':80.1534480601659, 'phi':10.1510817110481}, [(qx, qy)], [0.03514647218513852]],