In some applications of complex numbers, polar plots are necessary,
e.g., to plot the roots of a z-transform polynomial 
Hroo = roots(H);
polar( angle(Hroo), abs(Hroo), 'x' ), grid
Each root position will be marked with an 'x'.
Note that using plot on a complex vector will generate an
x--y plot that is similar to a polar plot, but the grid
function will not draw a polar grid as its does for the polar
plot.
