%--------------------------
 % @Author: Jingqiao Hu
 % @Date: 2021-01-25 21:10:08
 % @LastEditTime: 2021-02-08 16:37:18
%--------------------------
function F = deform_grad(sort_h, edofMat, dNh, eleNum_mi, U, regulated_matrix)

    eleNum_ma = size(edofMat, 1);

    initF = repmat([1;0;0;1], 1, eleNum_mi);
    F = cell(4, eleNum_ma);

    for ele = 1:eleNum_ma              
        edof = edofMat(ele, :);
        ue = U(edof); % including macro U and control pnts

        Re = regulated_matrix{ele};
        he = Re * ue;

        % reorder micro-displacement to [8 * eleNum_mi]
        he_reorder = sparse(sort_h(:,1), sort_h(:,2), he(sort_h(:,3)));

        %% 2. compute deform grad   
        for gp = 1:4
            Be = dNh{gp};
            F{gp, ele} = Be * he_reorder + initF; % 4 * eleNum_mi
        end
    end
end