wolffd@0: function h = draw_ellipse_axes(x, c, linespec)
wolffd@0: % DRAW_ELLIPSE_AXES(x, c, linespec)
wolffd@0: %   Draws the major and minor axes of ellipses.
wolffd@0: %   Ellipses are centered at x with covariance matrix c.
wolffd@0: %   x is a matrix of columns.  c is a positive definite matrix.
wolffd@0: %   linespec is optional.
wolffd@0: 
wolffd@0: [v,e] = eig(c);
wolffd@0: v = v*sqrt(e);
wolffd@0: 
wolffd@0: h = [];
wolffd@0: for j = 1:cols(v)
wolffd@0:   x1 = repmat(x(1,:),2,1) + repmat([-1;1]*v(1,j),1,cols(x));
wolffd@0:   x2 = repmat(x(2,:),2,1) + repmat([-1;1]*v(2,j),1,cols(x));
wolffd@0:   h = [h line(x1,x2)];
wolffd@0: end
wolffd@0: if nargin > 2
wolffd@0:   set_linespec(h,linespec);
wolffd@0: end