Sum of a signal in simulink

In my Simulink model, current value of a signal should be added to all previous value of the same signal. I've used integrator with initial value of zero to find it; however the result is different from what I find in Matlab through "sum" or "trapz" function. The solver is continuous with fixed step size. Any thought to resolve this issue. or any other block to use for this purpose instead of integrator?

Answer 1

[Azzi Abdelmalek]

You can use a Matlab function block with this code

function y=fcn(u)
persistent a
if isempty(a)
  a=0
end
y=u+a;
a=y;

You can also use a discrete transfer function 1/(z-1)

[Yeow Yu Leong]

or use an accumulator

Answer 2

[Sean de Wolski]

You could also use a unit delay:

[Azzi Abdelmalek]

He is asking for all previous values. This will calculate out(n)+out(n-1)