matthiasm@8: function h = draw_ellipse(x, c, outline_color, fill_color)
matthiasm@8: % DRAW_ELLIPSE(x, c, outline_color, fill_color)
matthiasm@8: %   Draws ellipses at centers x with covariance matrix c.
matthiasm@8: %   x is a matrix of columns.  c is a positive definite matrix.
matthiasm@8: %   outline_color and fill_color are optional.
matthiasm@8: 
matthiasm@8: n = 40;					% resolution
matthiasm@8: radians = [0:(2*pi)/(n-1):2*pi];
matthiasm@8: unitC = [sin(radians); cos(radians)];
matthiasm@8: r = chol(c)';
matthiasm@8: 
matthiasm@8: if nargin < 3
matthiasm@8:   outline_color = 'g';
matthiasm@8: end
matthiasm@8: 
matthiasm@8: h = [];
matthiasm@8: for i=1:cols(x)
matthiasm@8:   y = r*unitC + repmat(x(:, i), 1, n);
matthiasm@8:   if nargin < 4
matthiasm@8:     h = [h line(y(1,:), y(2,:), 'Color', outline_color)];
matthiasm@8:   else
matthiasm@8:     h = [h fill(y(1,:), y(2,:), fill_color, 'EdgeColor', outline_color)];
matthiasm@8:   end
matthiasm@8: end