28 using namespace gtsam;
 
   34   const Key x123 = 0, x45 = 1;
 
   35   gfg.
add(x123, (
Matrix(2, 3) << 1, 2, 3, 5, 6, 7).finished(),
 
   37   gfg.
add(x123, (
Matrix(2, 3) << 9, 10, 0, 0, 0, 0).finished(),
 
   38           x45,  (
Matrix(2, 2) << 11, 12, 14, 15.).finished(),
 
   56   gfg.
add(x123, Matrix23::Zero(), Vector2::Zero(), 
model);  
 
   57   gfg.
add(2, Matrix21::Zero(), Vector2::Zero(), 
model);