Merge pull request #22135 from mantidproject/22134_UnitCell_bug

Fix numerical error in UnitCell/ OrientedLattice
mantidproject · Mar 19, 2018 · 26e7693 · 26e7693
2 parents 64d0870 + 4e41c90
commit 26e7693
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Showing 2 changed files with 13 additions and 1 deletion.
diff --git a/Framework/Geometry/src/Crystal/UnitCell.cpp b/Framework/Geometry/src/Crystal/UnitCell.cpp
@@ -452,7 +452,13 @@ double UnitCell::recAngle(double h1, double k1, double l1, double h2, double k2,
   double E, ang;
   Q1 = Gstar * Q1;
   E = Q1.scalar_prod(Q2);
-  ang = acos(E / dstar(h1, k1, l1) / dstar(h2, k2, l2));
+  double temp = E / dstar(h1, k1, l1) / dstar(h2, k2, l2);
+  if (temp > 1)
+    ang = 0.;
+  else if (temp < -1)
+    ang = M_PI;
+  else
+    ang = acos(temp);
   if (angleunit == angDegrees)
     return rad2deg * ang;
   else

diff --git a/Framework/Geometry/test/UnitCellTest.h b/Framework/Geometry/test/UnitCellTest.h
@@ -142,6 +142,12 @@ class UnitCellTest : public CxxTest::TestSuite {
     }
   }
 
+  void testReciprocalAngle0() {
+    UnitCell cell(5.45, 5.45, 5.45);
+    TS_ASSERT_EQUALS(cell.recAngle(0., 4., 0., 0., 4., 0.), 0.);
+    TS_ASSERT_EQUALS(cell.recAngle(0., -4., 0., 0., 4., 0.), 180.);
+  }
+
   void testStrToUnitCell() {
     UnitCell cell(2.0, 4.0, 5.0, 90.0, 100.0, 102.0);
     std::string cellString = unitCellToStr(cell);