Changeset 6431056 in sasmodels for sasmodels/models/unified_power_Rg.py

Timestamp:

Jan 30, 2017 12:00:42 PM (7 years ago)

Author:

smk78

Branches:

master, core_shell_microgels, costrafo411, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests

Children:

cdcebf1

Parents:

3b9a526

Message:

Updated model docstrings for guinier_porod and unified_power_rg models
to explain relationship to one another, deficiency of unified_power_rg,
and add Hammouda references. (Relates to issue raised in email from
Jurrian, Jan 2017).

File:

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

sasmodels/models/unified_power_Rg.py

@@ -3 +3 @@
 ----------
 
-The Beaucage model employs the empirical multiple level unified
-Exponential/Power-law fit method developed by G. Beaucage. Four functions
-are included so that 1, 2, 3, or 4 levels can be used. In addition a 0 level
-has been added which simply calculates
+This model employs the empirical multiple level unified Exponential/Power-law 
+fit method developed by Beaucage. Four functions are included so that 1, 2, 3, 
+or 4 levels can be used. In addition a 0 level has been added which simply 
+calculates
 
 .. math::
@@ -15 +15 @@
 many different types of particles, including fractal clusters, random coils
 (Debye equation), ellipsoidal particles, etc.
+
+The model works best for *mass* fractal systems characterized by Porod exponents 
+between 5/3 and 3. It should not be used for *surface* fractal systems. Hammouda 
+(2010) has pointed out a deficiency in the way this model handles the 
+transitioning between the Guinier and Porod regimes and which can create 
+artefacts that appear as kinks in the fitted model function.
+
+Also see the Guinier_Porod model.
 
 The empirical fit function is:
@@ -56 +64 @@
 
 G Beaucage, *J. Appl. Cryst.*, 29 (1996) 134-146
+
+B Hammouda, *Analysis of the Beaucage model*, 
+*J. Appl. Cryst.*, (2010), 43, 1474–1478
 
 """