Changeset 9844c3a in sasmodels for doc/guide/plugin.rst

Timestamp:

Sep 27, 2017 12:44:40 PM (7 years ago)

Author:

Paul Kienzle <pkienzle@…>

Branches:

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

Children:

c0d7ab3

Parents:

0f48f1e

Message:

add note to the model writer about integer parameters

File:

• doc/guide/plugin.rst (modified) (1 diff)

doc/guide/plugin.rst

@@ -366 +366 @@
     dispersion.
 
+
+Integer Parameters
+..................
+
+Some models will have integer parameters, such as number of pearls in the
+pearl necklace model, or number of shells in the multi-layer vesicle model.
+The optimizers in BUMPS treat all parameters as floating point numbers which
+can take arbitrary values, even for integer parameters, so your model should
+round the incoming parameter value to the nearest integer inside your model
+you should round to the nearest integer.  In C code, you can do this using::
+
+    static double
+    Iq(double q, ..., double fp_n, ...)
+    {
+        int n = (int)(fp_n + 0.5);
+        ...
+    }
+
+in python::
+
+    def Iq(q, ..., n, ...):
+        n = int(n+0.5)
+        ...
+
+Derivatibve based optimizers such as Levenberg-Marquardt will not work
+for integer parameters since the partial derivative is always zero, but
+the remaining optimizers (DREAM, differential evolution, Nelder-Mead simplex)
+will still function.
 
 Model Computation