Hi all,
I have the following problem:
For the purpose of my analysis I have root trees with Branches containing
many leafs (all are simple floats/integers).
In order to get the cross-sections a number of (combinations of
) variables have to be extracted for different selections. These variables
and cuts are passed to the class as character strings.
e.g. I need to evaluate
cos(Thetah), cos(mc_Thetah),(Q2+0.59)^2.2/(Q2+1.02)^0.2,
goodevent&&BoxCut, Q2>2&&Q2<5&&t<1 etc...
There is a way to get it
tree->Draw("cos(Thetah):cos(mc_Thetah)",cut1)
double* var1 = tree->GetV1() // contains cos(Thetah)
double* var2 = tree->GetV2() // contains cos(mc_Thetah)
However for more than 3 variables and few cuts one has to loop MANY times
over the tree to get it. The I/O is the slowest operation and this is the
main limit on the speed of my calculations. For this reason I would like
to know if there is other way to do this
if there would be a method like double TTree::Eval(const char*
variable) or something more efficient so that one doesn't have to parse
the string by every call.
This would mean that after
tree->GetEntry(10)
var = tree->Eval("cos(Thetah)")
the var would contain the value of cos(Thetah) for entry 10
This way I could do all my calculation in one loop through the data.
Well, there is a way to do it if the variable is just a simple Leaf but is
there anything I could use to evaluate more complicated strings?
I think it must be already implemented somehow since the TTree::Draw()
uses it extensively but I couldn't find it anywhere and many people around
would be interested in this feature.
Best regards,
Miro
Version 3.05/05 5 June 2003 for linuxsuse6
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