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6b6cba33 1/**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 * *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
6 * *
7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
10 * copies and that both the copyright notice and this permission notice *
11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
13 * provided "as is" without express or implied warranty. *
14 **************************************************************************/
15
16/* $Id$ */
17
18///////////////////////////////////////////////////////////////////////////////
19//
20// Class to the track points on the Riemann sphere. Inputs are
21// the set of id's (volids) of the volumes in which residuals are
22// calculated to construct a chi2 function to be minimized during
23// the alignment procedures. For the moment the track extrapolation is
24// taken at the space-point reference plane. The reference plane is
25// found using the covariance matrix of the point
26// (assuming sigma(x)=0 at the reference coordinate system.
27//
8849da04 28// Internal usage of AliRieman class for minimization
29//
6b6cba33 30//////////////////////////////////////////////////////////////////////////////
31
3010c308 32#include <TArrayI.h>
33#include <TLinearFitter.h>
34#include <TMath.h>
35#include <TMatrixD.h>
36#include <TMatrixDSym.h>
37#include <TRandom.h>
38#include <TTreeStream.h>
39
24d4520d 40#include "AliLog.h"
8849da04 41#include "AliLog.h"
3010c308 42#include "AliRieman.h"
43#include "AliTrackFitterRieman.h"
98937d93 44
45ClassImp(AliTrackFitterRieman)
46
8849da04 47
98937d93 48AliTrackFitterRieman::AliTrackFitterRieman():
75e3794b 49 AliTrackFitter(),
dfce6628 50 fBCorrection(kFALSE),
75e3794b 51 fAlpha(0.),
52 fNUsed(0),
53 fConv(kFALSE),
54 fMaxDelta(3),
55 fRieman(new AliRieman(10000)), // allocate rieman
56 fDebugStream(new TTreeSRedirector("RiemanAlignDebug.root"))
98937d93 57{
58 //
59 // default constructor
60 //
98937d93 61}
62
63
64AliTrackFitterRieman::AliTrackFitterRieman(AliTrackPointArray *array, Bool_t owner):
75e3794b 65 AliTrackFitter(array,owner),
dfce6628 66 fBCorrection(kFALSE),
75e3794b 67 fAlpha(0.),
68 fNUsed(0),
69 fConv(kFALSE),
70 fMaxDelta(3),
71 fRieman(new AliRieman(10000)), //allocate rieman
72 fDebugStream(0)
98937d93 73{
74 //
75 // Constructor
76 //
8849da04 77 if (AliLog::GetDebugLevel("","AliTrackFitterRieman")) fDebugStream = new TTreeSRedirector("RiemanAlignDebug.root");
98937d93 78}
79
80AliTrackFitterRieman::AliTrackFitterRieman(const AliTrackFitterRieman &rieman):
75e3794b 81 AliTrackFitter(rieman),
dfce6628 82 fBCorrection(rieman.fBCorrection),
75e3794b 83 fAlpha(rieman.fAlpha),
84 fNUsed(rieman.fNUsed),
85 fConv(rieman.fConv),
86 fMaxDelta(rieman.fMaxDelta),
87 fRieman(new AliRieman(*(rieman.fRieman))),
88 fDebugStream(0)
98937d93 89{
90 //
91 // copy constructor
92 //
75e3794b 93 if (AliLog::GetDebugLevel("","AliTrackFitterRieman")) fDebugStream = new TTreeSRedirector("RiemanAlignDebug.root");
98937d93 94}
95
96//_____________________________________________________________________________
97AliTrackFitterRieman &AliTrackFitterRieman::operator =(const AliTrackFitterRieman& rieman)
98{
6b6cba33 99 //
100 // Assignment operator
98937d93 101 //
102 if(this==&rieman) return *this;
103 ((AliTrackFitter *)this)->operator=(rieman);
104
dfce6628 105 fBCorrection = rieman.fBCorrection;
8849da04 106 fAlpha = rieman.fAlpha;
107 fNUsed = rieman.fNUsed;
108 fConv = rieman.fConv;
186e6ced 109 fMaxDelta = rieman.fMaxDelta;
8849da04 110 fRieman = new AliRieman(*(rieman.fRieman));
75e3794b 111 fDebugStream = 0;
112 if (AliLog::GetDebugLevel("","AliTrackFitterRieman")) fDebugStream = new TTreeSRedirector("RiemanAlignDebug.root");
98937d93 113 return *this;
114}
115
8849da04 116
117AliTrackFitterRieman::~AliTrackFitterRieman(){
118 //
119 //
120 //
121 delete fRieman;
122 delete fDebugStream;
123}
124
98937d93 125void AliTrackFitterRieman::Reset()
126{
127 // Reset the track parameters and
128 // rieman sums
6b6cba33 129 //
98937d93 130 AliTrackFitter::Reset();
8849da04 131 fRieman->Reset();
98937d93 132 fAlpha = 0.;
46ae650f 133 fNUsed = 0;
98937d93 134 fConv =kFALSE;
135}
136
cc345ce3 137Bool_t AliTrackFitterRieman::Fit(const TArrayI *volIds,const TArrayI *volIdsFit,
98937d93 138 AliAlignObj::ELayerID layerRangeMin,
8849da04 139 AliAlignObj::ELayerID layerRangeMax)
98937d93 140{
141 // Fit the track points. The method takes as an input
cc345ce3 142 // the set of id's (volids) of the volumes in which
143 // one wants to calculate the residuals.
144 // The following parameters are used to define the
98937d93 145 // range of volumes to be used in the fitting
146 // As a result two AliTrackPointArray's obects are filled.
147 // The first one contains the space points with
cc345ce3 148 // volume id's from volids list. The second array of points represents
149 // the track extrapolations corresponding to the space points
98937d93 150 // in the first array. The two arrays can be used to find
cc345ce3 151 // the residuals in the volids and consequently construct a
98937d93 152 // chi2 function to be minimized during the alignment
153 // procedures. For the moment the track extrapolation is taken
cc345ce3 154 // at the space-point reference plane. The reference plane is
155 // found using the covariance matrix of the point
156 // (assuming sigma(x)=0 at the reference coordinate system.
dfce6628 157 Int_t debugLevel = AliLog::GetDebugLevel("","AliTrackFitterRieman");
158 Float_t debugRatio = 1./(1.+debugLevel);
98937d93 159
dfce6628 160 const Int_t kMinPoints =1;
98937d93 161 Int_t npoints = fPoints->GetNPoints();
dfce6628 162 if ( npoints<fMinNPoints) return kFALSE;
163 //
164 // fast count points
165 Int_t countFit = 0;
166 for (Int_t ifit=0; ifit<volIdsFit->GetSize(); ifit++){
167 Int_t volIdFit = volIdsFit->At(ifit);
168 for (Int_t ipoint = 0; ipoint < npoints; ipoint++)
169 if (volIdFit==fPoints->GetVolumeID()[ipoint]) countFit++;
170 }
171 if (countFit<fMinNPoints) return kFALSE;
172 //
173 Int_t countPoint = 0;
174 for (Int_t jpoint=0; jpoint<volIds->GetSize(); jpoint++){
175 Int_t volIdPoint = volIds->At(jpoint);
176 for (Int_t ipoint = 0; ipoint < npoints; ipoint++)
177 if (volIdPoint==fPoints->GetVolumeID()[ipoint]) countPoint++;
178 }
179 if (countPoint<kMinPoints) return kFALSE;
180 //
181 //
182
183 Reset();
184
185 if (fPoints && AliLog::GetDebugLevel("","AliTrackFitterRieman")>1&& gRandom->Rndm()<debugRatio){
8849da04 186 Int_t nVol = volIds->GetSize();
187 Int_t nVolFit = volIdsFit->GetSize();
188 Int_t volId = volIds->At(0);
189 (*fDebugStream)<<"PInput"<<
190 "NPoints="<<npoints<< // number of points
191 "VolId="<<volId<< // first vol ID
192 "NVol="<<nVol<< // number of volumes
193 "NvolFit="<<nVolFit<< // number of volumes to fit
194 "fPoints.="<<fPoints<< // input points
195 "\n";
196 }
98937d93 197
cc345ce3 198 Bool_t isAlphaCalc = kFALSE;
46ae650f 199 AliTrackPoint p,plocal;
cc345ce3 200// fPoints->GetPoint(p,0);
201// fAlpha = TMath::ATan2(p.GetY(),p.GetX());
98937d93 202
203 Int_t npVolId = 0;
46ae650f 204 fNUsed = 0;
98937d93 205 Int_t *pindex = new Int_t[npoints];
206 for (Int_t ipoint = 0; ipoint < npoints; ipoint++)
207 {
208 fPoints->GetPoint(p,ipoint);
209 UShort_t iVolId = p.GetVolumeID();
cc345ce3 210 if (FindVolId(volIds,iVolId)) {
98937d93 211 pindex[npVolId] = ipoint;
212 npVolId++;
213 }
cc345ce3 214 if (volIdsFit != 0x0) {
215 if (!FindVolId(volIdsFit,iVolId)) continue;
46ae650f 216 }
217 else {
218 if (iVolId < AliAlignObj::LayerToVolUID(layerRangeMin,0) ||
219 iVolId > AliAlignObj::LayerToVolUID(layerRangeMax,
c041444f 220 AliAlignObj::LayerSize(layerRangeMax))) continue;
46ae650f 221 }
cc345ce3 222 if (!isAlphaCalc) {
223 fAlpha = p.GetAngle();
224 isAlphaCalc = kTRUE;
225 }
46ae650f 226 plocal = p.Rotate(fAlpha);
186e6ced 227 if (TMath::Abs(plocal.GetX())>500 || TMath::Abs(plocal.GetX())<2 || plocal.GetCov()[3]<=0 ||plocal.GetCov()[5]<=0 ){
8849da04 228 printf("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</n");
229 p.Dump();
230 plocal.Dump();
231 printf("Problematic point\n");
232 printf("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</n");
186e6ced 233 }else{
234 AddPoint(plocal.GetX(),plocal.GetY(),plocal.GetZ(),
235 TMath::Sqrt(plocal.GetCov()[3]),TMath::Sqrt(plocal.GetCov()[5]));
8849da04 236 }
8849da04 237 // fNUsed++; AddPoint should be responsible
98937d93 238 }
239
8849da04 240 if (npVolId == 0 || fNUsed < fMinNPoints) {
98937d93 241 delete [] pindex;
242 return kFALSE;
243 }
244
245 Update();
cc345ce3 246
98937d93 247 if (!fConv) {
248 delete [] pindex;
249 return kFALSE;
250 }
251
252 if ((fParams[0] == 0) ||
253 ((-fParams[2]*fParams[0]+fParams[1]*fParams[1]+1) <= 0)) {
254 delete [] pindex;
255 return kFALSE;
256 }
257
cc345ce3 258
259 if (fNUsed < fMinNPoints) {
260 delete [] pindex;
261 return kFALSE;
262 }
263
46ae650f 264 fPVolId = new AliTrackPointArray(npVolId);
265 fPTrack = new AliTrackPointArray(npVolId);
98937d93 266 AliTrackPoint p2;
267 for (Int_t ipoint = 0; ipoint < npVolId; ipoint++)
268 {
269 Int_t index = pindex[ipoint];
270 fPoints->GetPoint(p,index);
186e6ced 271 if (GetPCA(p,p2) && (
272 TMath::Abs(p.GetX()-p2.GetX())<fMaxDelta &&
273 TMath::Abs(p.GetY()-p2.GetY())<fMaxDelta &&
274 TMath::Abs(p.GetZ()-p2.GetZ())<fMaxDelta
275 )) {
cc345ce3 276 Float_t xyz[3],xyz2[3];
277 p.GetXYZ(xyz); p2.GetXYZ(xyz2);
186e6ced 278 // printf("residuals %f %d %d %f %f %f %f %f %f\n",fChi2,fNUsed,fConv,xyz[0],xyz[1],xyz[2],xyz2[0]-xyz[0],xyz2[1]-xyz[1],xyz2[2]-xyz[2]);
46ae650f 279 fPVolId->AddPoint(ipoint,&p);
280 fPTrack->AddPoint(ipoint,&p2);
8849da04 281 }else{
282 // what should be default bahavior -
283 delete [] pindex;
284 delete fPVolId;
285 delete fPTrack;
286 fPVolId =0;
287 fPTrack =0;
288 return kFALSE;
98937d93 289 }
290 }
8849da04 291
dfce6628 292 if (AliLog::GetDebugLevel("","AliTrackFitterRieman")>0 && gRandom->Rndm()<debugRatio){
8849da04 293 //
294 // Debug Info
295 //
296 AliTrackPointArray *lPVolId = new AliTrackPointArray(npVolId);
297 AliTrackPointArray *lPTrack = new AliTrackPointArray(npVolId);
dfce6628 298 AliTrackPointArray *lPTrackE = new AliTrackPointArray(npVolId);
8849da04 299 AliRieman * residual = fRieman->MakeResiduals();
8849da04 300 for (Int_t ipoint = 0; ipoint < npVolId; ipoint++){
dfce6628 301 AliTrackPoint p0, p0local;
302 AliTrackPoint pFit, pFitlocal, pFitLocalE;
303 fPVolId->GetPoint(p0,ipoint);
304 Float_t lAngle = p0.GetAngle();
305 p0local= p0.MasterToLocal();
306 fPTrack->GetPoint(pFit,ipoint);
307 pFitlocal= pFit.Rotate(lAngle);
308 //
309 Float_t xyz[3], cov[3];
310 xyz[0] = pFitlocal.GetX();
311 xyz[1] = pFitlocal.GetY();
312 xyz[2] = pFitlocal.GetZ();
313 for (Int_t icov=0; icov<6; icov++) cov[icov]=0;
314 cov[3] = GetErrY2at(xyz[0]);
315 cov[5] = GetErrZ2at(xyz[0]);
316 pFitLocalE.SetXYZ(xyz,cov);
317 //
318 lPVolId->AddPoint(ipoint,&p0local);
319 lPTrack->AddPoint(ipoint,&pFitlocal);
320 lPTrackE->AddPoint(ipoint,&pFitLocalE);
8849da04 321 }
322 //
323 // debug info
324 //
325 Int_t nVol = volIds->GetSize();
326 Int_t nVolFit = volIdsFit->GetSize();
327 Int_t volId = volIds->At(0);
328 Int_t modId =0;
329 Int_t layer = AliAlignObj::VolUIDToLayer(volId,modId);
dfce6628 330 Int_t volIdFit = volIdsFit->At(0);
331 Int_t modIdFit =0;
332 Int_t layerFit = AliAlignObj::VolUIDToLayer(volIdFit,modIdFit);
8849da04 333
334 (*fDebugStream)<<"Fit"<<
335 "VolId="<<volId<< // volume ID
336 "Layer="<<layer<< // layer ID
337 "Module="<<modId<< // module ID
dfce6628 338 "LayerFit="<<layerFit<< // layer ID fit
339 "ModuleFit="<<modIdFit<< // module ID fit
8849da04 340 "NVol="<<nVol<< // number of volumes
341 "NvolFit="<<nVolFit<< // number of volumes to fit
342 "Points0.="<<fPVolId<< // original points
343 "Points1.="<<fPTrack<< // fitted points
344 "LPoints0.="<<lPVolId<< // original points - local frame
345 "LPoints1.="<<lPTrack<< // fitted points - local frame
dfce6628 346 "LPointsE.="<<lPTrackE<< // fitted points with ext error - local frame
8849da04 347 "Rieman.="<<this<< // original rieman fit
348 "Res.="<<residual<< // residuals of rieman fit
349 "\n";
350 delete lPVolId;
351 delete lPTrack;
352 delete residual;
353 }
98937d93 354
355 delete [] pindex;
98937d93 356 return kTRUE;
357}
358
8849da04 359
98937d93 360void AliTrackFitterRieman::AddPoint(Float_t x, Float_t y, Float_t z, Float_t sy, Float_t sz)
361{
362 //
8849da04 363 // add point to rieman fitter
98937d93 364 //
8849da04 365 fRieman->AddPoint(x,y,z,sy,sz);
366 fNUsed = fRieman->GetN();
98937d93 367}
368
8849da04 369
370
98937d93 371void AliTrackFitterRieman::Update(){
372 //
8849da04 373 //
98937d93 374 //
8849da04 375 fRieman->Update();
376 fConv = kFALSE;
377 if (fRieman->IsValid()){
378 for (Int_t ipar=0; ipar<6; ipar++){
379 fParams[ipar] = fRieman->GetParam()[ipar];
98937d93 380 }
8849da04 381 fChi2 = fRieman->GetChi2();
382 fNdf = fRieman->GetN()- 2;
383 fNUsed = fRieman->GetN();
384 fConv = kTRUE;
98937d93 385 }
dfce6628 386 //
387 //
388 //
389 TLinearFitter fitY(3,"pol2");
390 TLinearFitter fitZ(3,"pol2");
391 for (Int_t ip=0; ip<fRieman->GetN();ip++){
392 Double_t x = fRieman->GetX()[ip];
393 fitY.AddPoint(&x,fRieman->GetY()[ip]-fRieman->GetYat(x),1);
394 fitZ.AddPoint(&x,fRieman->GetZ()[ip]-fRieman->GetZat(x),1);
395 }
396 fitY.Eval();
397 fitZ.Eval();
398 for (Int_t iparam=0; iparam<3; iparam++){
399 fCorrY[iparam]=fitY.GetParameter(iparam);
400 fCorrZ[iparam]=fitZ.GetParameter(iparam);
401 }
402 fCorrY[3]=fitY.GetChisquare()/Float_t(fRieman->GetN()-3);
403 fCorrZ[3]=fitZ.GetChisquare()/Float_t(fRieman->GetN()-3);
98937d93 404}
405
dfce6628 406
407
6b6cba33 408//_____________________________________________________________________________
98937d93 409Bool_t AliTrackFitterRieman::GetPCA(const AliTrackPoint &p, AliTrackPoint &p2) const
410{
6b6cba33 411 //
98937d93 412 // Get the closest to a given spacepoint track trajectory point
413 // Look for details in the description of the Fit() method
6b6cba33 414 //
98937d93 415 if (!fConv) return kFALSE;
416
417 // First X and Y coordinates
418 Double_t sin = TMath::Sin(fAlpha);
419 Double_t cos = TMath::Cos(fAlpha);
420 // fParam[0] = 1/y0
421 // fParam[1] = -x0/y0
422 // fParam[2] = - (R^2 - x0^2 - y0^2)/y0
423 if (fParams[0] == 0) return kFALSE;
cc345ce3 424 // Track parameters in the global coordinate system
98937d93 425 Double_t x0 = -fParams[1]/fParams[0]*cos - 1./fParams[0]*sin;
426 Double_t y0 = 1./fParams[0]*cos - fParams[1]/fParams[0]*sin;
427 if ((-fParams[2]*fParams[0]+fParams[1]*fParams[1]+1) <= 0) return kFALSE;
6b6cba33 428 Double_t r = TMath::Sqrt(-fParams[2]*fParams[0]+fParams[1]*fParams[1]+1)/
98937d93 429 fParams[0];
430
cc345ce3 431 // Define space-point refence plane
432 Double_t alphap = p.GetAngle();
433 Double_t sinp = TMath::Sin(alphap);
434 Double_t cosp = TMath::Cos(alphap);
435 Double_t x = p.GetX()*cosp + p.GetY()*sinp;
436 Double_t y = p.GetY()*cosp - p.GetX()*sinp;
437 Double_t x0p= x0*cosp + y0*sinp;
438 Double_t y0p= y0*cosp - x0*sinp;
6b6cba33 439 if ((r*r - (x-x0p)*(x-x0p))<0) {
440 AliWarning(Form("Track extrapolation failed ! (Track radius = %f, track circle x = %f, space-point x = %f, reference plane angle = %f\n",r,x0p,x,alphap));
24d4520d 441 return kFALSE;
442 }
6b6cba33 443 Double_t temp = TMath::Sqrt(r*r - (x-x0p)*(x-x0p));
cc345ce3 444 Double_t y1 = y0p + temp;
445 Double_t y2 = y0p - temp;
446 Double_t yprime = y1;
447 if(TMath::Abs(y2-y) < TMath::Abs(y1-y)) yprime = y2;
448
449 // Back to the global coordinate system
450 Double_t xsecond = x*cosp - yprime*sinp;
451 Double_t ysecond = yprime*cosp + x*sinp;
452
453 // Now Z coordinate and track angles
454 Double_t x2 = xsecond*cos + ysecond*sin;
455 Double_t zsecond = GetZat(x2);
456 Double_t dydx = GetDYat(x2);
457 Double_t dzdx = GetDZat(x2);
458
459 // Fill the cov matrix of the track extrapolation point
460 Double_t cov[6] = {0,0,0,0,0,0};
461 Double_t sigmax = 100*100.;
462 cov[0] = sigmax; cov[1] = sigmax*dydx; cov[2] = sigmax*dzdx;
463 cov[3] = sigmax*dydx*dydx; cov[4] = sigmax*dydx*dzdx;
464 cov[5] = sigmax*dzdx*dzdx;
465
dfce6628 466 Double_t sigmay2 = GetErrY2at(x2);
467 Double_t sigmaz2 = GetErrZ2at(x2);
468 cov[3] += sigmay2;
469 cov[5] += sigmaz2;
470
471
cc345ce3 472 Float_t newcov[6];
473 newcov[0] = cov[0]*cos*cos-
474 2*cov[1]*sin*cos+
475 cov[3]*sin*sin;
476 newcov[1] = cov[1]*(cos*cos-sin*sin)-
477 (cov[3]-cov[0])*sin*cos;
478 newcov[2] = cov[2]*cos-
479 cov[4]*sin;
480 newcov[3] = cov[0]*sin*sin+
481 2*cov[1]*sin*cos+
482 cov[3]*cos*cos;
483 newcov[4] = cov[4]*cos+
484 cov[2]*sin;
485 newcov[5] = cov[5];
486
487 p2.SetXYZ(xsecond,ysecond,zsecond,newcov);
dfce6628 488 Int_t debugLevel = AliLog::GetDebugLevel("","AliTrackFitterRieman");
489 Float_t debugRatio = 1./(1.+debugLevel);
490 if (AliLog::GetDebugLevel("","AliTrackFitterRieman")>0 && gRandom->Rndm()<debugRatio){
8849da04 491 AliTrackPoint lp0(p);
492 AliTrackPoint lp2(p2);
dfce6628 493 (*fDebugStream)<<"PCA"<<
8849da04 494 "P0.="<<&lp0<<
495 "P2.="<<&lp2<<
496 "\n";
497 }
98937d93 498 return kTRUE;
499}
dfce6628 500
501Double_t AliTrackFitterRieman::GetYat(Double_t x) const {
502 //
503 // get y position at given point
504 //
505 Double_t correction=0;
506 if (fBCorrection){ // systematic effect correction
507 correction = fCorrY[0]+fCorrY[1]*x +fCorrY[2]*x*x;
508 }
509 return fRieman->GetYat(x)+correction;
510}
511
512Double_t AliTrackFitterRieman::GetZat(Double_t x) const {
513 //
514 // get z position at given point
515 //
516 Double_t correction=0;
517 if (fBCorrection){ // systematic effect correction
518 correction = fCorrZ[0]+fCorrZ[1]*x +fCorrZ[2]*x*x;
519 }
520 return fRieman->GetZat(x)+correction;
521}
522
523Double_t AliTrackFitterRieman::GetErrY2at(Double_t x) const {
524 //
525 // get estimate of extrapolation error
526 //
527 Double_t error = fRieman->GetErrY(x);
528 Double_t correction=0;
529 if (fBCorrection){ // everestimate error due systematic effect
530 error *=fCorrY[3];
531 correction = fCorrY[0]+fCorrY[1]*x +fCorrY[2]*x*x;
532 correction *=correction;
533 }
534 return TMath::Sqrt(error+correction);
535}
536
537Double_t AliTrackFitterRieman::GetErrZ2at(Double_t x) const {
538 //
539 // get estimate of extrapolation error
540 //
541 Double_t error = fRieman->GetErrZ(x)*fCorrZ[3];
542 Double_t correction=0;
543 if (fBCorrection){
544 error *= fCorrZ[3];
545 correction = fCorrZ[0]+fCorrZ[1]*x +fCorrZ[2]*x*x;
546 correction*= correction;
547 }
548 return TMath::Sqrt(error+correction);
549}
550