f=inline('-z+cos(x)','x','z'); % right-hand side z'=f(x,z) 
sol=inline('1/2*(cos(x)+sin(x)+exp(-x))','x'); % exact solution z(0)=1
h=0.2; %step size
[x1rk,z1rk]=rk2(f,[0,1],1,h) %RK2 approximations
h=0.1; %step size
[x2rk,z2rk]=rk2(f,[0,1],1,h) %RK2 approximations
h=0.05; %step size
[x3rk,z3rk]=rk2(f,[0,1],1,h) %RK2 approximations
ezplot(sol,[0,1]) %plotting exact solution
hold on
plot(x1rk,z1rk,'o') %plotting euler approx
plot(x2rk,z2rk,'*')
plot(x3rk,z3rk,'+')
legend('Exact', 'h=0.2', 'h=0.1', 'h=0.05')
title('Exact solution vs. RK2 approximations')
hold off