void Output::fixLeafOffsets( TBranch * b)
{
// recalculates the addresses for all the leaves.
//
// when constructing a branch with containing a variable length array with the index
// variable in the same branch it is not possible to specify the span of the index variable
// This span defaults to zero. When the addresses are asigned to the various leaves in the branch
// it calculates the size of the particular leaf (variable length array) in the buffer by looking
// at the span of the index variable - 0 in this case! using the method TLeaf::GetLen().
// The following code shoudl be applied to the branch after the spans of the index variables have been
// specified manually using the TLeaf::SetMaximum method. This time the GetLen method calculates the correct offset.
TObjArray * leaves = b->GetListOfLeaves();
char * addr = b->GetAddress();
int offset = 0;
int nleaves = leaves->GetEntriesFast();
// loop over the leaves:
for( int i =0; i < nleaves; ++i) {
TLeaf * leaf = (TLeaf *)leaves->UncheckedAt(i);
leaf->SetAddress( addr + offset );
int oldOffset = leaf->GetOffset();
leaf->SetOffset( offset );
//std::cout << " offset changed from : " << oldOffset << " to " << offset << std::endl;
TLeaf * index = leaf->GetLeafCount();
int nelements = 1;
if( index ) {
nelements = index->GetMaximum(); // deal with variable length arrays
} else {
nelements = leaf->GetLenStatic(); // deal with single variables and fixed length arrays
}
offset += leaf->GetLenType() * nelements;
}
}
/** @ingroup FMD_xsec_script
@param scale
@param filename
@param var
@param medName
@param thick
@param pdgName
*/
void
DrawXsection(Bool_t scale=kFALSE,
const char* filename="xsec.root",
const char* var="LOSS",
const char* medName="FMD_Si$",
Double_t thick=.03,
const char* pdgName="pi+")
{
TFile* file = TFile::Open(filename, "READ");
TTree* tree = static_cast<TTree*>(file->Get(Form("%s_%s",medName,
pdgName)));
TLeaf* tb = tree->GetLeaf("T");
TLeaf* vb = tree->GetLeaf(var);
if (!vb) {
std::cerr << "Leaf " << var << " not found" << std::endl;
return;
}
Float_t tkine, value;
tb->SetAddress(&tkine);
vb->SetAddress(&value);
Int_t n = tree->GetEntries();
Float_t xscale = 1;
Float_t yscale = 1;
if (scale) {
TDatabasePDG* pdgDb = TDatabasePDG::Instance();
TParticlePDG* pdgP = pdgDb->GetParticle(pdgName);
if (!pdgP) {
std::cerr << "Couldn't find particle " << pdgName << std::endl;
return;
}
Double_t m = pdgP->Mass();
Double_t q = pdgP->Charge() / 3;
if (m == 0 || q == 0) {
std::cerr << "Mass is 0" << std::endl;
return;
}
xscale = 1 / m;
yscale = 1 / (q * q);
}
TGraphErrors* graph = new TGraphErrors(n);
for (Int_t i = 0; i < n; i++) {
tree->GetEntry(i);
Double_t x = tkine*xscale;
Double_t y = value*yscale;
graph->SetPoint(i, x, y);
// 5 sigma
graph->SetPointError(i, 0, 5 * .1 * y);
}
TCanvas* c = new TCanvas("c","c");
c->SetLogx();
c->SetLogy();
graph->SetLineWidth(2);
graph->SetFillStyle(3001);
graph->SetFillColor(6);
graph->Draw("L");
graph->DrawClone("AL3");
c->Modified();
c->Update();
c->cd();
c->SaveAs("xsec.C");
}