Entity Queue not showing correct average waiting time and average queue length

I am trying to simulate a very simple M/M/1 system.

When I use the following code in Entity Generation, average waiting time and average Queue length are shown as zero: dt=-3*log(1-rand());

However, when I use the following code, those "l" and "w" values are as expected:

persistent rngInit;
if isempty(rngInit)
    seed = 12345;
    rng(seed);
    rngInit = true;
end

% Pattern: Exponential distribution
mu = 3;
dt = -mu * log(1 - rand());

Can someone please explain why?

I have also attached Bad and Good simulations based on version R2021a.

Answer 1

[Hornett]

Hi Amir,

I understand that you are facing an issue while building a simple M/M/1 system. I have reviewed your code, specifically the "Bad_Q.slx" file, and noticed that you have not seeded the random number generator. As a result, the entity server is serving requests faster than the entity generation, leading to zero values for "I" and "W" in "Bad_Q.slx".

To ensure accuracy and obtain consistent output from the random number generator, I recommend seeding the random value generator.