Compound matrix transformation [code attached]

Hello Experts,

I have the following code which shows the rotation of a 2D polygon and what i want is to modify it using a compound matrix transformation so that the square rotates about an arbitrary point.

Can anyone help me how can i do such a thing ??

Thanks in advance

close all;
clear all;
 
 
% a 2D pologyon 
p=[-1 1 1 -1 -1 ; -1 -1 1 1 -1];
 
% points p = in homogeneous coord
p(3,:)=1;
 
% axes for plotting the animation
figure; 
hold on;
axis([-6 6 -6 6]);
axis equal;
 
for theta=0:0.005:2*pi
 
    R=[cos(theta) -sin(theta) 0 ; sin(theta) cos(theta) 0 ; 0 0 1];
    
    pdash=R*p; 
    
    pdash(1,:)=pdash(1,:)./pdash(3,:);
    pdash(2,:)=pdash(2,:)./pdash(3,:);
    
    cla;
    plot(pdash(1,:),pdash(2,:),'b');   
    drawnow;
    
end

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