Uppgift 3

function [xut,yut]...
 =RKstep(f,x,y,h)
   k1=h*f(x,y);
   k2=h*f(x+h/2,y+k1/2);
   k3=h*f(x+h/2,y+k2/2);
   k4=h*f(x+h,y+k3);
   yut=y+(k1+2*k2+2*k3+k4)/6;
   xut=x+h;
end