%--------------------------
 % @Author: Jingqiao Hu
 % @Date: 2020-10-29 15:04:18
 % @LastEditTime: 2021-03-13 16:52:53
%--------------------------
% F(x) of every point x is 2*2:
%   [duxdx, duxdy
%    duydx, duydy];
% For one macro-ele & one gauss point:
% F(x) is sum of 4 nodes
%   [ux1, 2, 3, 4  *  [dN1dx, dN1dy
%    uy1, 2, 3, 4]     dN2dx, dN2dy
%                      dN3dx, dN3dy
%                      dN4dx, dN4dy]
function F = deform_grad_1scale(edofMat, U, gradN)
    eleNum = size(edofMat, 1);
    F = cell(4, 1);
    for gp = 1:4
        B = gradN{gp};
        Fm = zeros(4, eleNum);

        for ele = 1:eleNum
            edof = edofMat(ele, :);
            ue = reshape(U(edof), 2, []);
            
            Fe = eye(2) + ue * B'; % NOTE: + 1
            Fm(:, ele) = Fe(:);     
        end
        F{gp, 1} = Fm;
    end
end