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Forum: Biasing and Scoring
Re: Question Cross-section Biasing Weights
Date: 21 Aug, 2017
From: Marc Verderi <Marc Verderi>

Hello,

You may refer to our last general paper for some more details, but, to summarize, when you modify the interaction law (and changing the cross-section falls in this case) you have two types of weight to consider:

    - the weight for non-interaction, W_NI, over the step of length l
        - this the ratio of non-interaction probabilities over the step in the non-biased and biased schemes
        - in the case of cross-section change this is W_NI = exp[-(s_a-s_b)*l], where s_a and s_b are the analog and biased cross-sections respectively. In your case you have s_b > s_a hence -(s_a-s_b)*l > 0 and W_NI > 1 .

    - the weight for interaction at distance l, W_I
        - this the ratio of interaction probabilities at distance l into the non-biased and biased schemes
        - in the case of cross-section change this is W_I = s_a / s_b and is 0.5 in your case.

Then you have two possible cases :

    - a step 0 -> l ending with no interaction (eg : geometry boundary) at distance l : in this case the particle weight is multiplied by W_NI ; always > 1 in your case
    - a step 0 -> l ending with an interaction at distance l : in this case the particle weight is multiplied by W_NI * W_I ; which can take any positive value, including values above 1.

So having weights > 1 is indeed expected.

 Cheers,
 Marc

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1 Ok: Re: Cross-section Biasing Weights   (ljb - 22 Aug, 2017)
(_ None: Re: Cross-section Biasing Weights   (Marc Verderi - 23 Aug, 2017)
1 Question: Re: Cross-section Biasing Weights   (ljb - 28 Aug, 2017)
1 None: Re: Cross-section Biasing Weights   (Marc Verderi - 28 Aug, 2017)
2 Ok: Re: Cross-section Biasing Weights   (ljb - 28 Aug, 2017)
3 Ok: Re: Cross-section Biasing Weights   (ljb - 28 Aug, 2017)
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