Changeset db1d9d5 in sasmodels for sasmodels/models/flexible_cylinder.py

Timestamp:

Mar 28, 2019 3:16:51 PM (5 years ago)

Author:

Paul Kienzle <pkienzle@…>

Branches:

master, ticket-1257-vesicle-product, ticket_1156, ticket_822_more_unit_tests

Children:

8795b6f

Parents:

a34b811

Message:

merge with master

File:

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

sasmodels/models/flexible_cylinder.py

@@ -30 +30 @@
 The Kuhn length $(b = 2*l_p)$ is also used to describe the stiffness of a chain.
 
-The returned value is in units of $cm^{-1}$, on absolute scale.
-
 In the parameters, the sld and sld\_solvent represent the SLD of the cylinder
 and solvent respectively.
 
-Our model uses the form factor calculations implemented in a c-library provided
-by the NIST Center for Neutron Research (Kline, 2006).
-
-
-From the reference:
+Our model uses the form factor calculations in reference [1] as implemented in a
+c-library provided by the NIST Center for Neutron Research (Kline, 2006). This states:
 
     'Method 3 With Excluded Volume' is used.
@@ -46 +41 @@
     pseudocontinuous limit.
     See equations (13,26-27) in the original reference for the details.
+
+.. note::
+
+    There are several typos in the original reference that have been corrected
+    by WRC [2]. Details of the corrections are in the reference below. Most notably
+
+    - Equation (13): the term $(1 - w(QR))$ should swap position with $w(QR)$
+
+    - Equations (23) and (24) are incorrect; WRC has entered these into
+      Mathematica and solved analytically. The results were then converted to
+      code.
+
+    - Equation (27) should be $q0 = max(a3/(Rg^2)^{1/2},3)$ instead of
+      $max(a3*b(Rg^2)^{1/2},3)$
+
+    - The scattering function is negative for a range of parameter values and
+      q-values that are experimentally accessible. A correction function has been
+      added to give the proper behavior.
+
+
+**This is a model with complex behaviour depending on the ratio of** $L/b$ **and the
+reader is strongly encouraged to read reference [1] before use.**
 
 References
@@ -63 +80 @@
 `flexible_cylinder.c <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/flexible_cylinder.c>`_
 
+`wrc_cyl.c <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/lib/wrc_cyl.c>`_
+
 Authorship and Verification
 ----------------------------
 
-* **Author:** 
-* **Last Modified by:** 
-* **Last Reviewed by:** 
+* **Author:**
+* **Last Modified by:**
+* **Last Reviewed by:** Steve King **Date:** March 26, 2019
 * **Source added by :** Steve King **Date:** March 25, 2019
 """
@@ -76 +95 @@
 
 name = "flexible_cylinder"
-title = "Flexible cylinder where the form factor is normalized by the volume" \
+title = "Flexible cylinder where the form factor is normalized by the volume " \
         "of the cylinder."
 description = """Note : scale and contrast = (sld - sld_solvent) are both