%--------------------------
 % @Author: Jingqiao Hu
 % @Date: 2021-01-25 20:29:32
 % @LastEditTime: 2021-08-26 14:37:44

 % build micro stiffness matrix of simple version 
 % only depends on border and inner dofs 
%--------------------------
function M = build_M_simply(num_bdofs, K, bezier_B)
    k21 = K(num_bdofs+1 : end, 1 : num_bdofs) * bezier_B;
    k22 = K(num_bdofs+1 : end, num_bdofs+1 : end);
    M = - k22 \ k21;
end