I have made the above diagram and I placed the values of 1,1 as the parameters of INTEGRAL_f and GAINBLK_f respectively,and the other parameters are as default.
I have no idea why this graph is plotted since I thought that there should be no factor(s) which compose the exponential function.
Can anyone tell me what I am missing?
That's just math. You're have the system (here noted in the Laplace domain) y = 1/s*u and apply to it the positive feedback u = u+y, hence you end up (after solving for y) with the system y = 1/(s-1)*u, which is in state space, with your initial condition of integral block
x' = x+u,
x(0) = 1,
since you have no input, you obtain
x' = x,
x(0) = 1,
which yields x(t)=exp(t). If you want to see something interesting, just take 0 as initial condition of the integral block and add an input. However, if you keep this positive feedback your system is unstable...