|Message: Re: Cross-section Biasing Weights||Not Logged In (login)|
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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.
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