kindly explain the shuffling method of henon map?

[m,n]=size(A);
a = 3;
b = 3;
num_iter = 5;
for k=1:num_iter
    for i=1:m
        for j=1:n
            r = mod([round((1-(a*(i^2))+j)),round((b*i))],[m n]);
            S_img(i,j)=A(r(1)+1,r(2)+1);
        end
    end  
    A=S_img; 
end

[Walter Roberson]

https://ieeexplore.ieee.org/abstract/document/5054653