Added consistency check for Goresky--MacPherson stratifications

This *finally* fixes issue #30. I also had to update a test case because
it turns out I was using the wrong stratification. The results did *not*
change, though.

include/aleph/persistentHomology/PhiPersistence.hh

@@ -214,6 +214,19 @@ auto calculateIntersectionHomology( const aleph::topology::SimplicialComplex<Sim
   // original indexing, starting from k=2.
   bool useOriginalIndexing = is_goresky_macpherson_perversity<Perversity>::value;
 
+  if( useOriginalIndexing )
+  {
+    // Consistency check: The stratification must have sufficiently many
+    // simplicial complexes.
+    if( X.size() <= 2 )
+      throw std::runtime_error( "Insufficient number of simplicial complexes for stratification" );
+
+    // Consistency check: The strata need to satisfy $X_{n-1} = X_{n-2}$
+    // for a proper Goresky--MacPherson stratification.
+    if( *(X.rbegin()+1) != *(X.rbegin()+2) )
+      throw std::runtime_error( "Stratification must satisfy requirements by Goresky & MacPherson" );
+  }
+
   // 0. Check consistency of strata.
   // 1. Create permissibility function based on the dimensionality of
   //    the intersection of simplices with individual strata.

tests/test_persistent_intersection_homology.cc

@@ -639,7 +639,7 @@ template <class T> void testTorus()
   aleph::topology::Skeleton skeleton;
   auto X0 = skeleton(0, K);
   auto X1 = skeleton(1, K);
-  auto X2 = K;
+  auto X2 = X1;
   auto X3 = K;
 
   auto D2 = aleph::calculateIntersectionHomology( L, {X0,X1,X2,X3}, aleph::PerversityGM( {0,0} ) );