Changeset 38d8774 in sasmodels

Timestamp:

Nov 25, 2015 1:09:28 PM (9 years ago)

Author:

Paul Kienzle <pkienzle@…>

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:

319ab14

Parents:

82d239a

Message:

improve single precision accuracy using 2sin^{2(x/2) = 1-cos(x)}

File:

• sasmodels/models/lamellar.py (modified) (1 diff)

sasmodels/models/lamellar.py

@@ -81 +81 @@
     const double sub = sld - solvent_sld;
     const double qsq = q*q;
-    return 4.0e-4*M_PI*sub*sub/qsq * (1.0-cos(q*thickness))
-        / (thickness*qsq);
+    // Original expression
+    //return 4.0e-4*M_PI*sub*sub/qsq * (1.0-cos(q*thickness)) / (thickness*qsq);
+    // const double alpha = fmod(q*thickness+0.1, 2.0*M_PI)-0.1;
+    // Use small angle fix 1-cos(theta) = 2 sin^2(theta/2)
+    const double sinq2 = sin(0.5*q*thickness);
+    return 4.0e-4*M_PI*sub*sub/qsq * 2.0*sinq2*sinq2 / (thickness*qsq);
     """