More random random number

Wondering what people think is the best way to generate a more random random number stream (one that doesn't look exactly the same after each compile).

I thought of using a version of the real time to set the stream: eg

int temp_no = realtime(2)%100;
uniform(1,100,temp_no);

But flexsim isn't liking how i'm using modulo? Any comments on syntax and/or methodology appreciated, have only just started looking into the random number topic in any detail.

Regards
Paul

Hi Paul,

use the fmod command for your modulo.

double i=realtime(2);
int m=fmod(i,100);

pt("Stream:");
pd(m);
pr();

The % is the operator for the modulo in C and it is also in the Flexsim doc but I could not get it working either. So I guess it should be fixxed or taken out of the doc.


Otherwise this is a nice way to randomize you random streams.

Have you tried changing the environment settings to "Initialise Random Number Streams Based on System Time" under File->Global Preferences->Environment?

Might be worth a look to see if it meets your needs.

You are correct in that the % command is currently contained in the documentation and needs to be updated to the fmod command that is used in Flexscript. This is a known problem (with the documentation) that we hope to fix for a future release.

You could also make an On Post-Compile trigger (in Tools>Model Triggers) with something like this:
randinit(0,realtime(1)*realtime(2));

The easiest way to do it is, as Jason suggested, by just checking the box in Global Preferences. However, I just checked it, and unfortunately there's a bug there where it doesn't save the preference properly. We'll fix this in the next release. To fix it yourself, execute the following script in a Script window:

treenode env = node("VIEW:/environment");
nodeinsertinto(env);
nodeadddata(last(env), DATATYPE_NUMBER);
setname(last(env), "seedbysystemtime");

Once you've done that, go back to Global Preferences, check the box, apply the change, then close Flexsim, and it should be saved the next time you open Flexsim.

Thankyou all for your feedback.

The global preferences option works really well and solves my problem. I would suggest documenting such a useful feature, including for example explaining when this initialisation occurs (i'm guessing on compile or on reset?).

Kind Regards
Paul