Changeset 70530778 in sasmodels

Timestamp:

Aug 23, 2018 8:38:30 PM (6 years ago)

Author:

Paul Kienzle <pkienzle@…>

Branches:

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

Children:

c11d09f

Parents:

0168844

Message:

avoid cancellation error causing NaN values to appear in 2D patterns

File:

• sasmodels/kernel_iq.c (modified) (2 diffs)

sasmodels/kernel_iq.c

@@ -84 +84 @@
   out_spin = clip(out_spin, 0.0, 1.0);
   // Previous version of this function took the square root of the weights,
-  // under the assumption that 
+  // under the assumption that
   //
   //     w*I(q, rho1, rho2, ...) = I(q, sqrt(w)*rho1, sqrt(w)*rho2, ...)
@@ -188 +188 @@
     QACRotation *rotation,
     double qx, double qy,
-    double *qa_out, double *qc_out)
+    double *qab_out, double *qc_out)
 {
+    // Indirect calculation of qab, from qab^2 = |q|^2 - qc^2
     const double dqc = rotation->R31*qx + rotation->R32*qy;
-    // Indirect calculation of qab, from qab^2 = |q|^2 - qc^2
-    const double dqa = sqrt(-dqc*dqc + qx*qx + qy*qy);
-
-    *qa_out = dqa;
+    const double dqab_sq = -dqc*dqc + qx*qx + qy*qy;
+    //*qab_out = sqrt(fabs(dqab_sq));
+    *qab_out = dqab_sq > 0.0 ? sqrt(dqab_sq) : 0.0;
     *qc_out = dqc;
 }