Bugfix in method writeDisplacement

The transfer from the periodic to the non-periodic basis was wrong.

src/quasiconvexity-test.cc

@@ -99,7 +99,7 @@ void writeDisplacement(const Basis& basis, const Vector& periodicX, const FieldM
 
   // Add the underlying affine displacement.  For this we need
   // a representation in a non-periodic basis.
-  BCRSMatrix<double> matrix;
+  BCRSMatrix<FieldMatrix<double,2,2> > matrix;
   assembleGlobalBasisTransferMatrix(matrix, basis, nonperiodicPowerBasis);
 
   Vector nonperiodicX(nonperiodicBasis.size());