function xdot = f (x, t)
K = 0;
xdot = zeros (3,1);
xdot(1) = 77.27 * (x(2) - x(1)*x(2) + x(1) - 8.375e-06*x(1)^2);
xdot(2) = (x(3) - x(1)*x(2) - x(2)) / 77.27;
xdot(3) = 0.161*(x(1) - x(3)) + K;
if mod(t,5) == 0  % How can i say "every 5 time step" ??
  K = x(3) + 2;
else
  K = 0;
endif
endfunction




t = linspace (0, 1, 100); % Time step is 1 or it changes in reason of algorithm method??

y = lsode ("f", [1;2;1], t);

plot (t,y);
print('esempio.ps', '-deps');