Here is some C++ code and an associated makefile to find effective volumes from AraSim output files.

It computes error bars on the effective volumes using the relevant AraSim function.

Compile like "make -f veff.mk"

Run like "./veff thrown_radius thrown_depth AraOut.1.root AraOut.2.root...."

#include <iostream>
#include <fstream>
#include <sstream>
#include <math.h>
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <time.h>
#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <cstring>
#include <unistd.h>

#include "TTreeIndex.h"
#include "TChain.h"
#include "TFile.h"
#include "TTree.h"
#include "TMath.h"

#include "Event.h"
#include "Detector.h"
#include "Report.h"
#include "Vector.h"
#include "counting.hh"

using namespace std;

//Get effective volumes with error bars

class EarthModel;

int main(int argc, char **argv)
{
	gStyle->SetOptStat(111111);
	gStyle->SetOptDate(1);
	
	if(argc<4){
		cout<<"Not enough arguments! Abort run."<<endl;
		cout<<"Run like: ./veff volradius voldepth AraOut1.root AraOut2.rot ..."<<endl;
		return -1;
	}

	double volradius = atof(argv[1]);
	double voldepth = atof(argv[2]);

	TChain *AraTree = new TChain("AraTree");
	TChain *AraTree2 = new TChain("AraTree2");

	for(int i=3; i<argc;i++){
		AraTree->Add(string(argv[i]).c_str());
		AraTree2->Add(string(argv[i]).c_str());
	}

	Report *report = 0;
	Event *event=0;
	AraTree2->SetBranchAddress("report",&report);
	AraTree2->SetBranchAddress("event",&event);

	int totnthrown = AraTree2->GetEntries();
	cout << "Total number of events: " << totnthrown << endl;

	int NBINS=10;
	double eventsfound_binned[NBINS];
	for(int i=0; i<NBINS; i++) eventsfound_binned[i]=0.;

	double totweight=0;
	for(int iEvt2=0; iEvt2<totnthrown; iEvt2++){
		AraTree2->GetEntry(iEvt2);
		if(report->stations[0].Global_Pass<=0) continue;
		double weight = event->Nu_Interaction[0].weight;
		if(weight > 1.0) continue;
		totweight += weight;

		int index_weights = Counting::findWeightBin(log10(weight));
		if(index_weights<NBINS) eventsfound_binned[index_weights]++;
	}

	double error_minus=0.;
	double error_plus=0.;
	Counting::findErrorOnSumWeights(eventsfound_binned,error_plus,error_minus);

	double vtot = TMath::Pi() * double(volradius) * double(volradius) * double(voldepth) / 1.e9; //answer in km^3
	double veff = vtot * totweight / double(totnthrown) * 4. * TMath::Pi(); //answer in km^3 sr
	double veff_p  = vtot * (error_plus) / double(totnthrown) * 4. * TMath::Pi(); //answer in km^3 sr
	double veff_m  = vtot * (error_minus) / double(totnthrown) * 4. * TMath::Pi(); //answer in km^3 sr
                                                                                                                          
	printf("volthrown: %.6f \n  totweight: %.6f + %.6f - %.6f \n  Veff: %.6f + %.6f - %.6f \n",
			vtot,
			totweight, error_plus, error_minus,
			veff, veff_p, veff_m
			);
	return 0;
}

#############################################################################
##
##Changes:
##line 54 - OBJS = .... add filename.o      .... del oldfilename.o
##line 55 - CCFILE = .... add filename.cc     .... del oldfilename.cc
##line 58 - PROGRAMS = filename
##line 62 - filename : $(OBJS)
##
##############################################################################
include StandardDefinitions.mk

#Site Specific  Flags
ifeq ($(strip $(BOOST_ROOT)),)
	BOOST_ROOT = /usr/local/include
endif
SYSINCLUDES	= -I/usr/include -I$(BOOST_ROOT)
SYSLIBS         = -L/usr/lib
DLLSUF = ${DllSuf}
OBJSUF = ${ObjSuf}
SRCSUF = ${SrcSuf}

CXX = g++

#Generic and Site Specific Flags
CXXFLAGS     += $(INC_ARA_UTIL) $(SYSINCLUDES) 
LDFLAGS      += -g $(LD_ARA_UTIL) -I$(BOOST_ROOT) $(ROOTLDFLAGS) -L. 

# copy from ray_solver_makefile (removed -lAra part)

# added for Fortran to C++

LIBS	= $(ROOTLIBS) -lMinuit $(SYSLIBS) 
GLIBS	= $(ROOTGLIBS) $(SYSLIBS)


LIB_DIR = ./lib
INC_DIR = ./include

#ROOT_LIBRARY = libAra.${DLLSUF}

OBJS = Vector.o EarthModel.o IceModel.o Trigger.o Ray.o Tools.o Efficiencies.o Event.o Detector.o Position.o Spectra.o RayTrace.o RayTrace_IceModels.o signal.o secondaries.o Settings.o Primaries.o counting.o RaySolver.o Report.o eventSimDict.o veff.o
CCFILE = Vector.cc EarthModel.cc IceModel.cc Trigger.cc Ray.cc Tools.cc Efficiencies.cc Event.cc Detector.cc Spectra.cc Position.cc RayTrace.cc signal.cc secondaries.cc RayTrace_IceModels.cc Settings.cc Primaries.cc counting.cc RaySolver.cc Report.cc veff.cc
CLASS_HEADERS = Trigger.h Detector.h Settings.h Spectra.h IceModel.h Primaries.h Report.h Event.h secondaries.hh #need to add headers which added to Tree Branch

PROGRAMS = veff

all : $(PROGRAMS) 
	
veff : $(OBJS)
	$(LD) $(OBJS) $(LDFLAGS)  $(LIBS) -o $(PROGRAMS) 
	@echo "done."

#The library
$(ROOT_LIBRARY) : $(LIB_OBJS) 
	@echo "Linking $@ ..."
ifeq ($(PLATFORM),macosx)
# We need to make both the .dylib and the .so
		$(LD) $(SOFLAGS)$@ $(LDFLAGS) $(G77LDFLAGS) $^ $(OutPutOpt) $@
ifneq ($(subst $(MACOSX_MINOR),,1234),1234)
ifeq ($(MACOSX_MINOR),4)
		ln -sf $@ $(subst .$(DllSuf),.so,$@)
else
		$(LD) -dynamiclib -undefined $(UNDEFOPT) $(LDFLAGS) $(G77LDFLAGS) $^ \
		   $(OutPutOpt) $(subst .$(DllSuf),.so,$@)
endif
endif
else
	$(LD) $(SOFLAGS) $(LDFLAGS) $(G77LDFLAGS) $(LIBS) $(LIB_OBJS) -o $@
endif

##-bundle

#%.$(OBJSUF) : %.$(SRCSUF)
#	@echo "<**Compiling**> "$<
#	$(CXX) $(CXXFLAGS) -c $< -o  $@

%.$(OBJSUF) : %.C
	@echo "<**Compiling**> "$<
	$(CXX) $(CXXFLAGS) $ -c $< -o  $@

%.$(OBJSUF) : %.cc
	@echo "<**Compiling**> "$<
	$(CXX) $(CXXFLAGS) $ -c $< -o  $@

# added for fortran code compiling
%.$(OBJSUF) : %.f
	@echo "<**Compiling**> "$<
	$(G77) -c $<


eventSimDict.C: $(CLASS_HEADERS)
	@echo "Generating dictionary ..."
	@ rm -f *Dict* 
	rootcint $@ -c ${INC_ARA_UTIL} $(CLASS_HEADERS) ${ARA_ROOT_HEADERS} LinkDef.h

clean:
	@rm -f *Dict*
	@rm -f *.${OBJSUF}
	@rm -f $(LIBRARY)
	@rm -f $(ROOT_LIBRARY)
	@rm -f $(subst .$(DLLSUF),.so,$(ROOT_LIBRARY))	
	@rm -f $(TEST)
#############################################################################