BUG FIX: Assemble the mass matrix properly

src/one-body-sample.cc

@@ -240,7 +240,7 @@ int main(int argc, char *argv[]) {
 
       {
         MassAssembler<GridType, P1Basis::LocalFiniteElement,
-                      P1Basis::LocalFiniteElement> const localMass;
+                      P1Basis::LocalFiniteElement, SmallMatrix> const localMass;
         OperatorAssembler<P1Basis, P1Basis>(p1Basis, p1Basis)
             .assemble(localMass, massMatrix);
         massMatrix *= density;