This is the stiffness matrix computed by Matlab:
(1, 1) -> -10.851
(4, 1) -> 2.1701
(5, 1) -> 1.0851
(7, 1) -> 2.1701
(8, 1) -> -1.0851
(10, 1) -> 1.0851
(13, 1) -> 2.1701
(14, 1) -> 1.0851
(16, 1) -> 2.1701
(17, 1) -> -1.0851
(19, 1) -> 1.0851
(2...