[RR, JJ] = meshgrid(-10:1:10, -10:1:10);
RRdot = a.*JJ; %Note the use of .* and .^
JJdot = -b.*RR;
figure(2)
hold on
quiver(RR,JJ,RRdot, JJdot)
axis([-10 10 -10 10])
set(gca,'Box','Off');
set(figure(2),'color','white');


