[Rivet] Displacing histograms

[Andy Buckley]

On 29/11/12 16:26, James Monk wrote:
> Hi everyone,
> 
> I'm implementing a Rivet analysis in which the final plots involve taking the ratio of two temporary histograms, before shifting the whole lot down by the average multiplicity for the run.  I can obviously go through point-by-point on the scatter plot and shift each one down (and in principle deal with the additional statistical error on the multiplicity, which will be very small), but I was wondering if anyone knows of a more elegant way of doing that.  It's a bit of an unusual case, so I'm not surprised there's no method to do that.

There's a nice way to do it in YODA :-) Well, niceish... it's still C++!
Maybe we should *really* get that released as soon as possible!

In Rivet-with-YODA it would be something like this. First, because

---
struct XShifter {
    XShifter(double shift) : xshift(shift) {  }
    double operator()(double x) { return x - xshift; }
};

divide(tmp1, tmp2, destScatter2DPtr);
transformX(destScatter2DPtr, XShifter(Nmean));
---

The XShifter struct (or class) is inelegant, but blame C++ for that.
Maybe the Boost lambda stuff would work, too. It's only necessary
because your Nmean is only known at the end of the run: a fixed offset
could be done with just a double -> double function.

In AIDA.... yep, completely by-hand DataPointSet mangling, I guess!

Andy

-- 
Dr Andy Buckley, SUPA Advanced Research Fellow
Particle Physics Expt Group, University of Edinburgh

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