false binning in plot_view plots

Bug #1199408 reported by Khaled Teilab
This bug affects 1 person
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Bug Description

I am calculating cross section for particles production in nucleon-nucleon collisions using calchep. I use the pcm_cycle script to scan over a range of incoming particle momenta. I use the plot_view script to look at the results and save them in form of a .math file.
What I have noticed is that the results are always shifted by half of the step size used in pcm_cycle.
What I mean is that calchep calculates the cross section at say pcm=a, pcm=a+stepsize pcm=a+2*stepsize and so on.
But when I look at the corresponding .math file produced by plot_view, I have no point at pcm=a or pcm=a+stepsize, rather I have points at a+(stepsize/2), a+(3 * stepsize/2) and so on.
This bug leads to a shift of the whole curve obtained by half a stepsize to the right. At threshold where the cross section rises very rapidly, this effect is crucial.

Attached you can find 3 curves of the same reaction using 3 different step sizes which exactly illustrates the problem if you look at the start of the spectrum. When the change in cross section is not the big, it doesn't matter a lot. But at threshold the effect is very huge. Please keep in mind the starting pcm value for the three calculations (a) was exactly the same. Nevertheless the curves start at different values due to the interpolation

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Khaled Teilab (teilab) wrote :
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