Random Seed

ROOT
1

How does one set a seed for the random number generator?

That is, how do I get:

TH1F* h = new TH1F("test","test",8,0,50); h->FillRandom("gaus",50);
to give me a different plot every time the code is run.

Thanks

2

By default you get a different distribution every time you call FillRandom.
This function uses the currently defined random generator pointed by gRandom (it is a TRandom3 object by default).

Rene

3

I get the same distribution every time I run the program. If I keep drawing new histograms the distribution changes, but the cycle is the same every time.

4

Of course if you run your program twice and by default you get teh same distribution. I imagine the disaster otherwise.
Please have a look at the TRandom, TRandom3 classes how to set a new seed every time you run the program, ie in your case call

gRandom = new TRandom3(0);
root.cern.ch/root/html/TRandom3. … 3:TRandom3

Rene

5

This is functionally equivalent to

gRandom->SetSeed (0);

except that you’re not leaking memory, right?

Charles

6

correct

Rene