Changeset 6b4f7f6 in sasmodels for sasmodels/models/star_polymer.py

Timestamp:

Mar 22, 2016 1:51:26 PM (8 years ago)

Author:

richardh

Branches:

master, core_shell_microgels, costrafo411, magnetic_model, release_v0.94, release_v0.95, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests

Children:

55b2b232

Parents:

e664a11

Message:

renamed variables, sorted issues in doc

File:

• sasmodels/models/star_polymer.py (modified) (6 diffs)

sasmodels/models/star_polymer.py

@@ -1 +1 @@
 r"""
-Calculates the scattering from fractal-like aggregates based on
-the Mildner reference. This model is also known as the Benoit Star model.
+The Benoit model for a simple star polymer, with Gaussian coils arms from 
+a common point.
 
 Definition
@@ -25 +25 @@
     u = \left\langle R_{g}^2\right\rangle q^2
 
-is the square of the ensemble average radius-of-gyration of an arm.
+contains the square of the ensemble average radius-of-gyration of an arm.  Note that 
+when there is only one arm, $f$ = 1, the Debye Gaussian coil equation is recovered.
+Star polymers in solutions tend to have strong interparticle and osmotic effects, so 
+the Benoit equation may not work well. At small q the Guinier term and hence I(q=0)
+is the same as for $f$ arms of radius of gyration $R_g$, as described for the :ref:`mono_gauss_coil <mono-gauss-coil>`.
 
 
-Reference
----------
+References
+----------
 
 H Benoit *J. Polymer Science*, 11, 596-599 (1953)
@@ -41 +45 @@
 title = "Star polymer model with Gaussian statistics"
 description = """
-        Scattering model class for 'Star polymer with Gaussian statistics'
+        Benoit 'Star polymer with Gaussian statistics'
         with
         P(q) = 2/{fv^2} * (v - (1-exp(-v)) + {f-1}/2 * (1-exp(-v))^2)
@@ -47 +51 @@
         - v = u^2f/(3f-2)
         - u = <R_g^2>q^2, where <R_g^2> is the ensemble average radius of
-        giration squared of an arm
+        gyration squared of an arm
         - f is the number of arms on the star
         """
@@ -54 +58 @@
 # pylint: disable=bad-whitespace, line-too-long
 #             ["name", "units", default, [lower, upper], "type","description"],
-parameters = [["radius2", "Ang", 100.0, [0.0, inf], "", "Ensemble radius of gyration squared of an arm"],
+parameters = [["rg_squared", "Ang^2", 100.0, [0.0, inf], "", "Ensemble radius of gyration SQUARED of an arm"],
               ["arms",    "",      3,   [1.0, 6.0], "", "Number of arms in the model"],
              ]
@@ -62 +66 @@
 
 demo = dict(scale=1, background=0,
-            radius2=100.0,
+            rg_squared=100.0,
             arms=3.0)
 
 oldname = 'StarPolymer'
 
-oldpars = dict(radius2='R2',
+oldpars = dict(rg_squared='R2',
                arms='arms')
 
-tests = [[{'radius2': 2.0,
+tests = [[{'rg_squared': 2.0,
            'arms':    3.3,
           }, 0.5, 0.851646091108],
 
-         [{'radius2':    1.0,
+         [{'rg_squared':    1.0,
            'arms':       2.0,
            'background': 1.8,
           }, 1.0, 2.53575888234],
         ]
+# 23Mar2016  RKH edited docs, would this better use rg not rg^2 ? Numerical noise at extremely small q.rg