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Re: Bear Smear and Cross Sections [message #13886 is a reply to message #13885] Mon, 27 August 2012 09:22 Go to previous messageGo to previous message
Ingo Froehlich is currently offline  Ingo Froehlich
Messages: 167
Registered: March 2004
Location: IKF - Frankfurt
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From: *dip.t-dialin.net
Michael Kunkel wrote on Fri, 24 August 2012 19:32


Also, I am unclear on what SetNpx/y does. Looking in the code I see that on line 58
if (npy>0) pf2->SetNpx(npy);

Is this suppose to be SetNpx for npy? Could you also elaborate more on this functionality?



This is just a typical copy-and-paste typo. I will correct it.

SetNpx/Npy are just forwarded to the TF2 base class. They have the same meaning as there (precision vs. computing time)

Michael Kunkel wrote on Fri, 24 August 2012 19:32



Also, beam smearing is not working with the PScatterCrossSection. ....

....
Quote:


PS: Do not forget that the y-axis (a linear increase of _f) was just dummy.


I do not understand this. Once I corrected my sytax for my double boost, I checked my distributed cos(theta) of the PLUTO generation. It looks like the input. (see below) Would you also elaborate more on on the meaning of your P.S.

Thanks
Michael



I think I should explain the meaning of this method a little bit more. It is a function based on _x (cos theta) and _y (total c.m. energy). The class samples the density function with GetRandom2(), and sets the resulting angle and the c.m. energy of the system. Therefore, the beam smearing cannot be used in this case. You have to fold the beam smearing inside the function.

All this could be in fact also be realized with a TF2 class. But the class PF2EvalBatch is more flexible. You can merge one (or more) histograms with the function, if you want you can use one histogram for cos theta and another one for the cross section (and/or beam smearing), or a 2dimensional histogram, or just an analytical function. Therefore, in my dummy example you have the replace the calculation of _y (linear function) with some meaningful (if you look carefully you can also see the dummy linear function in your plot).

I have chosen c.m. instead of beam energy because it is an invariant. This is important if somebody uses the class for near-threshold sampling in a deuteron or heavy nucleon with fermi momentum.




--
Ingo Froehlich
IKF - University of Frankfurt
069-798-47027, FAX: -47024

[Updated on: Mon, 27 August 2012 09:22]

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