%--------------------------
 % @Author: Jingqiao Hu
 % @Date: 2021-05-18 23:02:33
 % @LastEditTime: 2021-05-18 23:02:34
%--------------------------
function M = assembleM2(num_b, K, bezier_B)
    k21 = K(num_b + 1 : end, 1 : num_b) * bezier_B;
    k22 = K(num_b + 1 : end, num_b+1 : end);
%     tic
    M = - k22 \ k21;
%     toc
end