Re: [fluka-discuss]: Normalization for the 2nd step of a two-step process

From: Vittorio Boccone <>
Date: Fri, 15 Nov 2013 16:08:02 +0000

Hi Mina,
 I assume you are saving the file with those line (which I extracted from the previous long topic)

WTRACK is indeed the weight of the particle with respect to primary that generated it.

You get 717984 particle from the first step out of 702M, to be used as primaries for the second step.

For this reason you must apply an additional normalization factor 717984/702M to the weight of the
primary which you load in the second step.

You then loop over the 700K particle (400M times) in a random way or sequentially. The random seed
history is what makes the history of the particle different. You just need to be sure that this 700K
are a representative sample of your real distribution.

Best regards

Dr. Vittorio Boccone - University of Geneva

o Address:
 UniGe: Département de physique nucléaire et corpusculaire
        24 Quai Ernest-Ansermet, CH-1211 Geneve 4, Switzerland
 CERN: CERN, CH-1211 Geneve 23, Switzerland

o E-mail:<> (professional)<> (private)

On 14 Nov 2013, at 23:06, Mina Nozar <<>> wrote:

Hello everyone,

I am not sure of the normalization in the 2nd step of a two-step process.

In the first step:

I write out particles I am interested in (type and boundary) crossing via mgdraw.f and USRDUMP. Since I am using importance biasing in the first step, I write out the weights as well.

So in the output file I have lines like this:

Id, x, y, z, cosx, cosy, cosz, kinetic energy, weight
8 -.2635E+03 0.6864E+02 0.2944E+04 -0.6332783577022189E+00 -0.3722034999484587E+00 -0.6785448226109299E+00 0.6606E-06 0.6400E-05
7 -.2635E+03 0.6589E+02 0.2946E+04 -0.4822515648543289E+00 -0.8047950128287192E+00 0.3460323908560768E+00 0.8389E-03 0.2133E-06
7 -.2635E+03 0.7252E+02 0.2941E+04 -0.7274812055368878E+00 0.1436728665088557E+00 -0.6709166885834075E+00 0.1702E-03 0.2133E-06

Out of the 702M primaries in the first step, I get 717984 particles written out.

In the second step:

Using source.f, I read in the above info. and assign the particle weights:

 WTFLK(NPFLKA) = Weight(line)

Manual says WEIPRI is the total weight of the primary particles. So is this basically the sum of weights (column 7 above) of particles that get read in? Does WEIPRI get written out somewhere?

I then set up several runs (450 M events). So I think the way I understand it, the program loops over the 717984 several times to get to the 450 M primaries. But does the looping happen in a random way? Am I correct to think that the sum of column 7 in the input file IS NOT equal to the WEIPRI?

And my last question is how to normalize information in (per primary) from the second step, given the above?

Thank you very much,
Received on Fri Nov 15 2013 - 17:59:04 CET

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