#Linear stability domain for explicit 3 stage RK method of order 3
restart;
with(plots):
# Warning, the name changecoords has been redefined
r:=1+z+1/2*z^2+1/6*z^3;

z:=x+I*y;

contourplot(abs(r),x=-3..3,y=-3..3,contours=[1],
   numpoints=1000,axes=boxed,view=[-3..3,-3..3]);