ost crashed, if not enough atoms fulfilled the distance threshold to

build superposable subsets. At least three atoms are required.
This scenario gets now checked and an error is thrown.

modules/mol/alg/src/svd_superpose.cc

@@ -289,6 +289,13 @@ SuperpositionResult MeanSquareMinimizerImpl::IterativeMinimize(int max_cycles, R
     transformed_atoms = this->TransformEMatX(atoms1_, transformation_matrix);
     matching_indices = this->CreateMatchingSubsets(transformed_atoms, atoms2_, distance_threshold);
 
+    if(matching_indices.size()<3){
+      std::stringstream ss;
+      ss<<"Failed to Converge, less than 3 superposable atoms in iteration ";
+      ss<<cycles<<"!";
+      throw Error(ss.str());
+    }
+
     subset1 = EMatX::Zero(matching_indices.size(),3);
     subset2 = EMatX::Zero(matching_indices.size(),3);
 

modules/mol/alg/tests/test_superposition.cc

@@ -25,7 +25,8 @@
 #include <boost/test/unit_test.hpp>
 #include <boost/test/auto_unit_test.hpp>
 #include <ost/mol/mol.hh>
- #include <ost/mol/builder.hh>
+#include <ost/mol/builder.hh>
+#include <ost/message.hh>
 
 using namespace ost;
 using namespace ost::mol;
@@ -96,6 +97,26 @@ BOOST_AUTO_TEST_CASE(iterative_superposition_svd)
   BOOST_CHECK(res_1.fraction_superposed==1.0);
   BOOST_CHECK(res_2.fraction_superposed==7.0/8.0);
   BOOST_CHECK(res_3.ncycles==3);
+
+  EntityHandle eh_2_atoms = Builder()
+                              .Chain("A")
+                                .Residue("D")
+                                  .Atom("A",geom::Vec3(0,0,0))
+                                  .Atom("B",geom::Vec3(0,0,0));
+
+  //Error, that has to be thrown during initialization of superposition object
+  BOOST_CHECK_THROW(IterativeSuperposeSVD(eh_2_atoms.CreateFullView(),
+                                          eh_2_atoms.CreateFullView(),
+                                          1,5.0,false), Error);
+
+  //forces an error, since there won't be enough atoms within the distance 
+  //threshold after the first superposition.
+  ed.SetAtomPos(atoms[0],geom::Vec3(50,50,50));
+  ed.SetAtomPos(atoms[1],geom::Vec3(50,50,50));
+  ed.SetAtomPos(atoms[2],geom::Vec3(50,50,50));
+  ed.SetAtomPos(atoms[3],geom::Vec3(50,50,50));
+
+  BOOST_CHECK_THROW(IterativeSuperposeSVD(ev1, ev2, 5, 5.0, false), Error);
 }