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  #1  
Old 05-29-2008
Paul Dowling Paul Dowling is offline
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Default 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

Last edited by Paul Dowling; 05-30-2008 at 12:00 AM.
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Old 05-30-2008
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Nico Zahn Nico Zahn is offline
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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.
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kind regards Nico.
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Old 05-30-2008
Jason Lightfoot Jason Lightfoot is offline
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Default Environment Settings

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.
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Old 05-30-2008
Dustin Derrick Dustin Derrick is offline
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Default

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.
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Old 05-30-2008
Alex Christensen Alex Christensen is offline
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You could also make an On Post-Compile trigger (in Tools>Model Triggers) with something like this:
randinit(0,realtime(1)*realtime(2));
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Old 05-30-2008
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Anthony Johnson Anthony Johnson is offline
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Default

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:
Code:
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.
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  #7  
Old 06-01-2008
Paul Dowling Paul Dowling is offline
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Default

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
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