Given a function handle f an initial condition y0 and a final time tf, solve numerically the differential equation
dy/dt = f(y)
for the function y(t) between t=0 and t=tf. Give as a result res=y(tf).
f = @(x) -x; tf= 1; y0= 1;
=> y(tf) = 1/e = 0.367879441171442
Remarks: aim at a relative precision of around 1e-6. The function is analytic in the interval [0,1].