Adding an arrow to a polar plot

Is there any way to add an arrow to a polar plot? I want to show the orientation of a polar curve.

This is the curve that I am plotting:

t = 0:pi/100:2*pi;

r = abs((2+cos(t)).*(exp(2*1i*t)));

the = angle((2+cos(t)).*exp(2*1i*t));

polar(the,r)

Answer 1

[Rebecca Krosnick]

There is not a single function or property in MATLAB that will allow you to add arrows to a polar plot to indicate orientation, but the following code will accomplish this. It uses the "quiver" function to display velocity vectors of the curve:

t = 0:pi/100:2*pi;
r = abs((2+cos(t)).*(exp(2*1i*t)));
the = angle((2+cos(t)).*exp(2*1i*t));
polar(the,r)
[X,Y] = pol2cart(the,r); % get Cartesian coordinates

factor = 5; % sampling ratio; factor=5 means the arrow will be drawn for every 5th point on the curve
i = 1; % index into quiver array
j = factor * factor; % index into X,Y Cartesian coordinates
u = []; % array for x component of quiver vector
v = []; % array for y component of quiver vector
xt = []; % array for x position of quiver vector
yt = []; % array for y position of quiver vector
while (j+1) <= length(X)
  xt(i) = X(j);
  yt(i) = Y(j);

    u(i) = X(j+1) - X(j);
    v(i) = Y(j+1) - Y(j);

    i = i + 1;
    j = i*factor;
end
hold on;
quiver(xt, yt, u, v);

A couple aspects of this code you may want to modify:

• The arrow length is not normalized
• The arrows on the edge of the circular axes are cut off. The MATLAB Answers post at the following link provides a workaround for changing the circular axes radius: http://www.mathworks.com/matlabcentral/answers/102174-how-to-change-the-axis-limits-and-remove-alter-the-ticks-and-labels-for-a-compass-polar-plot