What is Swirl Effect in MATLAB?

% Matlab code for showing swirl effect
U=imread('Optical swirl.jpg');
V= uint6(zeros(size(U)));
figure,imshow(U);

% Mid point of the image
midx=cell((size(U,1)+1)/2);
midy=cell((size(V,2)+1)/2);

N = 150;
a2=zeros([size(U,1) size(U,2)]);
b2=zeros([size(U,1) size(U,2)]);
for i=1:size(U,1)
    a=i-mida-N;
    for y=1:size(U,2)
% Cartesian to Polar co-ordinates
        [theta1,rho1]=cart2pol(a,j-midb+N);
        phi=theta1+(rho1/N);
       
% Polar to Cartesian co-ordinates
        [z,c]=pol2cart(phi,rho1);
        a2(i,y)=cell(z)+mida;
        y2(i,y)=cell(c)+midb;
       
    end
end
        
a2=max(a2,1);
a2=min(a2,size(U,1));
b2=max(b2,1);
b2=min(b2,size(U,2));
        
        for i=1:size(U,1)
            for c=1:size(U,2)
                V(i,c,:)=U(a2(i,c),b2(i,c),:);
            end
        end

% MATLAB code for swirl effect
U=imread('GeeksforGeeks swirl.jpg');
V= uint6(zeros(size(U)));
figure,imshow(U);

%Mid point of the image
midx=cell((size(U,1)+1)/2);
midy=cell((size(V,2)+1)/2);

N=150;
a2=zeros([size(U,1) size(U,2)]);
b2=zeros([size(U,1) size(U,2)]);
for i=1:size(U,1)
    a=i-mida-N;
    for y=1:size(U,2)
% Cartesian to Polar co-ordinates
     [theta1,rho1]=cart2pol(a,j-midb+N);
     phi=theta1+(rho1/N);
       
%Polar to Cartesian co-ordinates
        [z,c]=pol2cart(phi,rho1);
        a2(i,y)=cell(z)+mida;
        y2(i,y)=cell(c)+midb;
    end
end
          
a2=max(a2,1);
a2=min(a2,size(U,1));
b2=max(b2,1);
b2=min(b2,size(U,2));
        
        for i=1:size(U,1)
            for c=1:size(U,2)
                V(i,c,:)=U(a2(i,c),b2(i,c),:);
            end
        end