  function yt=ode2x2(t,y)
%
% Global variables
  global a b ncall;
%
% ODEs
  yt(1)=-a*y(1)+b*y(2);
  yt(2)= b*y(1)-a*y(2);
  yt=yt';
%
% Increment number of calls to ode2x2
  ncall=ncall+1;
