>> help rectangle
rectangle Create rectangle, rounded-rectangle, or ellipse.
rectangle adds a default rectangle to the current axes.
rectangle('Position', [x y w h]) adds a rectangle at the
specified position.
rectangle('Curvature', [0 0], ...) creates a rectangle.
rectangle('Curvature', [1 1], ...) creates an ellipse.
rectangle('Curvature', [x y], ...) creates a rectangle with
rounded corners where x and y are between 0 and 1 and represent
the normalized amount of curvature. Horizontal curvature (x)
is the fraction of the width of the position rectangle which is
curved. Vertical curvature (y) is the fraction of the height
of the position rectangle which is curved.
rectangle returns a handle to a rectangle object. RECTANGLEs are
children of AXES objects.
The rectangle object will not render at axes View angles other than
[0 90].
Execute GET(H), where H is a rectangle handle, to see a list of
rectangle object properties and their current values. Execute SET(H)
to see a list of rectangle object properties and legal property
values.
%以原点为中心，画一个半径2的圆
rectangle('Curvature', [1 1], 'Position',[0,0,2,2]); axis image