%--------------------------
 % @Author: Jingqiao Hu
 % @Date: 2021-05-03 21:19:15
 % @LastEditTime: 2021-05-03 21:19:16
%--------------------------
function [bdofs, idofs] = micro_boundary(microx)
    Num_node = (1+microx)^3;
    nodenrs = reshape(1:Num_node, 1+microx, 1+microx, 1+microx);
    
    % extract surface nodes
    inner = nodenrs(2:end-1, 2:end-1, 2:end-1);
    boundarys = setdiff(nodenrs(:), inner(:));
    
    bdofs = nodes2dofs(boundarys);
    idofs = nodes2dofs(inner);
end