I already tested this, but something must be wrong with my code:
Matrix m =new Matrix();
m.rotateX((float)(0.5*Math.PI));
SimpleVector v1=new SimpleVector(0,1,0);
v1.matMul(m);
m.invert3x3();
v1.matMul(m);
JOptionPane.showMessageDialog(null, v1, "v1", JOptionPane.ERROR_MESSAGE);
In the messageDialog v1 is (0.0,-1.0,8.742278E-8) and i thought it should be (0,1,0).