Changeset 7c35fda in sasmodels for sasmodels/kernel_iq.c

Timestamp:

May 31, 2018 10:07:31 AM (6 years ago)

Author:

Adam Washington <adam.washington@…>

Branches:

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

Children:

befe905

Parents:

84e89cd

Message:

Document reason for change in I(q)

File:

• sasmodels/kernel_iq.c (modified) (1 diff)

sasmodels/kernel_iq.c

@@ -83 +83 @@
   in_spin = clip(in_spin, 0.0, 1.0);
   out_spin = clip(out_spin, 0.0, 1.0);
-  // Note: sasview 3.1 scaled all slds by sqrt(weight) and assumed that
+  // Previous version of this function took the square root of the weights,
+  // under the assumption that 
+  //
   //     w*I(q, rho1, rho2, ...) = I(q, sqrt(w)*rho1, sqrt(w)*rho2, ...)
-  // which is likely to be the case for simple models.
+  //
+  // However, since the weights are applied to the final intensity and
+  // are not interned inside the I(q) function, we want the full
+  // weight and not the square root.  Any function using
+  // set_spin_weights as part of calculating an amplitude will need to
+  // manually take that square root, but there is currently no such
+  // function.
   weight[0] = (1.0-in_spin) * (1.0-out_spin); // dd
   weight[1] = (1.0-in_spin) * out_spin;       // du