Mat Object: 1 MPI processes
  type: seqaij
row 0: (0, 5.)  (1, 2.)  (3, 3.) 
row 1: (1, 9.)  (2, 7.) 
row 2: (0, 10.)  (2, 12.) 
row 3: (1, 13.)  (3, 15.) 
IS Object: 1 MPI processes
  type: stride
Index set is permutation
Number of indices in (stride) set 2
0 0
1 1
IS Object: 1 MPI processes
  type: stride
Number of indices in (stride) set 2
0 2
1 3

Explicit Schur complement of (0,0) in (1,1)
Mat Object: 1 MPI processes
  type: seqdense
1.5111111111111111e+01 -6.0000000000000009e+00 
-1.0111111111111111e+01 1.5000000000000000e+01 

Explicit Schur complement of (1,1) in (0,0)
Mat Object: 1 MPI processes
  type: seqdense
5.0000000000000000e+00 -6.0000000000000009e-01 
-5.8333333333333330e+00 9.0000000000000000e+00 

Preconditioning Schur complement of (0,0) in (1,1)
Mat Object: 1 MPI processes
  type: seqaij
row 0: (0, 12.)  (1, -6.) 
row 1: (0, -10.1111)  (1, 15.) 

After update
Mat Object: 1 MPI processes
  type: seqaij
row 0: (0, 13.)  (1, -5.) 
row 1: (0, -9.1)  (1, 16.) 
