%
function square_transform(len,angle_rad)
%
% Square transform - rotation.
%
% Input: 
%              1. len - the side of the square;
%              2.  angle_rad - the angle in radians, by which the square
%                             should be rotated.
%
  a=-len/2; % the corner of the square - bottom-left
  b=-len/2;
  
  x(1)=a;
  x(2)=x(1)+len;
  x(3)=x(2); 
  x(4)=x(1);
  x(5)=x(1);
  %--------------------
  y(1)=b;
  y(2)=y(1);
  y(3)=y(2)+len;
  y(4)=y(3);
  y(5)=y(1);
 
 v0=[x;y]; % v(1,i) - row 1, column i.
 
 Transform_M=[ [cos(angle_rad) sin(angle_rad)];
                               [-sin(angle_rad) cos(angle_rad)]]; 
                            % do not forget (-) minus sign.
 v=Transform_M*v0;
 
 for i=1:4   
    % line([x(i) x(i+1)],[y(i) y(i+1)]);
    line([v(1,i) v(1,i+1)] , [v(2,i),v(2,i+1)]);
      % text(x(i),y(i),num2str(i)); 
 end % i
 %