Merge pull request espressomd#2341 from RudolfWeeber/vs_tracers_witho…

…ut_lb

Core: VS tracers: don't complain about missing lb for non-virtual par…

src/core/virtual_sites/VirtualSitesInertialessTracers.cpp

@@ -24,6 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "errorhandling.hpp"
 #include "lattice.hpp"
 #include "virtual_sites/lb_inertialess_tracers.hpp"
+#include <algorithm>
 
 void VirtualSitesInertialessTracers::after_force_calc() {
   // Now the forces are computed and need to go into the LB fluid
@@ -39,7 +40,13 @@ void VirtualSitesInertialessTracers::after_force_calc() {
     return;
   }
 #endif
-  runtimeErrorMsg() << "Inertialess Tracers: No LB method was active.";
+  if (std::any_of(local_cells.particles().begin(),
+                  local_cells.particles().end(),
+                  [](Particle &p) { return p.p.is_virtual != 0; })) {
+    runtimeErrorMsg() << "Inertialess Tracers: No LB method was active but "
+                         "virtual sites present.";
+    return;
+  }
 }
 
 void VirtualSitesInertialessTracers::after_lb_propagation() {

testsuite/python/virtual_sites_tracers_common.py

@@ -242,3 +242,18 @@ def test_triel(self):
         self.assertGreater(dist2non, 2)
         self.assertAlmostEqual(dist2weak, np.sqrt(2), delta=0.3)
         self.assertAlmostEqual(dist2strong, np.sqrt(2), delta=0.1)
+
+    def test_zz_without_lb(self):
+        """Check behaviour without lb. Ignore non-virtual particles, complain on 
+        virutal ones.
+
+        """
+        system = self.system
+        system.virtual_sites = VirtualSitesInertialessTracers()
+        system.actors.clear()
+        system.part.clear()
+        p = system.part.add(pos=(0, 0, 0))
+        system.integrator.run(1)
+        p.virtual = 1
+        with(self.assertRaises(Exception)):
+            system.integrator.run(1)