Problems with SolverNC for CQN with class with jobs more than 50 and mutliple FCFS stations

[Lavanya Chawla]

Hi I was using LINE to build a CQN model with multiple FCFS stations, a processor sharing station and an infinite server station (see example file).
I noticed a discreprancy between the results for SolverNC between class with jobs =49 and jobs=50, Both SolverMVA and SolverJMT do not exhibit such behavior:

NC results for
* Jobs = 49
Station JobClass QLen Util RespT ResidT Tput
___ __ _ _ __ _ ____

Station11     class       15.211    0.96632    15.741    15.741    0.96632
Station21     class      0.93269    0.48316    0.9652    0.9652    0.96632
Station31     class       6.4241    0.77306     3.324     6.648     1.9326
Station12     class       15.211    0.96632    15.741    15.741    0.96632
Station22     class      0.93269    0.48316    0.9652    0.9652    0.96632
Station32     class       6.4241    0.77306     3.324     6.648     1.9326
IS1           class       1.9326     1.9326         1         2     1.9326
IS2           class       1.9326     1.9326         1         2     1.9326

• Jobs = 50
  Station JobClass QLen Util RespT ResidT Tput
  ___ __ __ __ _ _____

  Station11 class 22392 28721 0.77964 0.77964 28721
  Station21 class 0.3952 14360 1.376e-05 1.376e-05 28721
  Station31 class 91907 22976 1.6 3.2001 57441
  Station12 class 22392 28721 0.77964 0.77964 28721
  Station22 class 0.3952 14360 1.376e-05 1.376e-05 28721
  Station32 class 91907 22976 1.6 3.2001 57441
  IS1 class 57441 57441 1 2 57441
  IS2 class 57441 57441 1 2 57441

I also noticed that if there are multiple FCFS stations with different service rates, a processor sharing station and an infinite server station, the model does not have product form solutions. If one of the FCFS stations is changed to a PS station or the service rates are made same, the model then has product form solutions.

I'm currently not sure why either of these is happening so any information about this would be helpful.
Thank you.
Lavanya

[Giuliano Casale]

Hi, many thanks for flagging this problem, a patch will be released in the next version. The current issue is that N=50 is a threshold in NC to switch to an approximate method, but your model is single class and in that case it can be solved efficiently also with an exact method.

So for the moment being can you run it as SolverNC(model,'exact').getAvgTable, that will solve the problem.

[Giuliano Casale]

I spotted a second independent issue, your model does have product form in all cases you mention so , you can find attached the patch to fix that. Network.m goes under src/lang/@Network, the other two files under src/api. They will also be included in a future patch.

[Lavanya Chawla]

Thank you!