odefun=@(t,x)[(8.94*x(3)*(1-x(1))-3.31*x(1)*x(2))/(0.58*x(1)+0.18*x(2)+1.5*x(3)+2.98);...
     (8.94*x(3)*(1-x(1))-3.31*x(1)*x(2))/(0.58*x(1)+0.18*x(2)+1.5*x(3)+2.98)-2.26*x(2)/(x(2)+2*x(3));...
     -0.5*(8.94*x(3)*(1-x(1))-3.31*x(1)*x(2))/(0.58*x(1)+0.18*x(2)+1.5*x(3)+2.98)-0.006*x(3)/(x(2)+2*x(3))];
[t,x]=ode45(odefun,[0 3],[0 0 1]);
plot(t,x)
legend('t-X','t-Y','t-S')

Variable t=[0,3],X=0,Y=0,S=1;
Plot x,y,s;
ConstStr f=(8.94*S*(1-X)-3.31*X*Y)/(0.58*X+0.18*Y+1.5*S+2.98);
ODEFunction X'=f;
            Y'=f-2.26*Y/(Y+2*S);
            S'=(-f-0.012*S/(Y+2*S))/2;