Pseudo Randomness

Each time i run Flexsim, different things happen . . Duh, that's what randomness means!

However, sometimes:

• i will want the same thing to happen each time
  • to test individual sub sections
  • to see how more than one scenario compares with another, with all else equal
• or need to be able to replicate results, very important for some situations.

I know of at least one other simulation package that uses pseudo random input, calculated from a seed.

Does anyone know if there is an easy way to do this?

Thanks

Kenny

Flexsim will reset the random streams with the same seed value whenever the model is reset IF you select the "Repeat Random Streams" option under the Statistics menu. If you want to be in control of the seed value, you can explicitly reset a particular stream with a particular seed value of your choosing with the randinit() command.

Oops! Well i did ask for an easy answer; that was embarassingly easy -

Thanks Cliff

I'd recommend using a random seed for initialisation between 1 and 2147483647. You can put the code below on a reset User Event and make sure your User Events folder is at the top of the Tools folder. This will make your replications repeatable should you later wish to run one of them individually.

int  totalstreams=50;        //the number of streams you want to initialize
int  streambase=100;                //The starting stream offset - could be 0 too
int  firstreplication=getnodenum(node("/project/exec/replications/Current",maintree()));
int  replication=0;
if  (firstreplication==0)
    replication=1;                      //reset button has probably been hit
else
  replication=getnodenum(node("/project/exec/replications/CurrentRunOfScenario",maintree()));
//replication=30;                      // un-comment this line to initialise the streams for a particular replication
randinit(0,replication);              //we'll user stream zero to initialize the other streams' seeds
for (int n=1;n<=totalstreams;n++){
   randinit(streambase+n,duniform(1,2147483647,0));
}

Streams 0-100 (therefore 101 streams) are reset by flexsim so I'm using 101 and higher here (just to be sure )

Thanks Jason

I'm not so strong on C++ yet but that makes sense. I'll definately use this code once i'm up to speed.

Cheers

Kenny

ps - Say Hi to Mike Ellarby, it was him that put me onto Flexsim in the first place - at OR Society SW08. I liked it so much that I sought out the Australian/NZ disrtibutor role.

My post above refers to a User Commands folder but it should be User Events.

For some reason I can't edit my posting.