f = @(t,y) (y + 2*t*exp(2*t));
[x, y] = ODE_Euler_explicit(f,0,1,1);
z = 2*(x-1).*exp(2*x) + 3*exp(x);
plot(x,y);
hold on
plot(x,z);
sqrt((y-z)*(y-z)')
[x, v] = ODE_Euler_implicit(f,0,1,1);
plot(x,v);
sqrt((v-z)*(v-z)')