function [t,u,e] = ssrkc4(neqn,t0,u0,h)
   [ut0]=derv(neqn,t0,u0);
   u=u0+ut0*h;
   t=t0+h;
   [ut]=derv(neqn,t,u);
   e=(ut-ut0)*h/2;
   u=u+e;
