Plot an ellipse give in cartesian form on the XY plane.

src/plot_ellipse_2d.m

+function h = plot_ellipse_2d( f, npoints)
+%PLOT_ELLIPSE_2D Plot an ellipse in XY plane.
+
+    if nargin < 2
+        npoints = 20;
+    end
+    
+    x0      = f(1);
+    y0      = f(2);
+    a       = f(3);
+    b       = f(4);
+    theta   = f(5);
+
+    R = [   cos( theta ) sin( theta ) ;
+        -sin( theta ) cos( theta ) ] ;
+    
+    t = linspace( 0 , 2 * pi, npoints )';
+    XY0 = [ a * sin(t), b * cos(t) ];
+    XY1 = XY0 * R;
+    xr = XY1( :, 1 ) + x0;
+    yr = XY1( :, 2 ) + y0;
+    
+    xr = [ xr ; xr(1,:) ];
+    yr = [ yr ; yr(1,:) ];
+    h = line( xr, yr );
+
+end
+