[u/mrichter/AliRoot.git] / TPC / AliTPCExBFirst.cxx

/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

////
// This implementation AliTPCExB is using an aproximate calculation of the ExB
// effect. Therefore the drift ODE is Taylor expanded and only the first
// order part is taken.
////

#include "TMath.h"
#include "AliFieldMap.h"
#include "AliMagF.h"
#include "TTreeStream.h"
#include "AliTPCExBFirst.h"

ClassImp(AliTPCExBFirst)

const Double_t AliTPCExBFirst::fgkEM=1.602176487e-19/9.10938215e-31;
const Double_t AliTPCExBFirst::fgkDriftField=40.e3;

AliTPCExBFirst::AliTPCExBFirst()
  : fDriftVelocity(0),
    fkNX(0),fkNY(0),fkNZ(0),
    fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
    fkZMin(-250.),fkZMax(250.),
    fkNMean(0),
    fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
  //
  // purely for I/O
  //
}

AliTPCExBFirst::AliTPCExBFirst(const AliMagF *bField,
			       Double_t driftVelocity,
			       Int_t nx,Int_t ny,Int_t nz)
  : fDriftVelocity(driftVelocity),
    fkNX(nx),fkNY(ny),fkNZ(nz),
    fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
    fkZMin(-250.),fkZMax(250.),
    fkNMean(0),
    fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
  //
  // The constructor. One has to supply a magnetic field and an (initial)
  // drift velocity. Since some kind of lookuptable is created the
  // number of its meshpoints can be supplied.
  //
  ConstructCommon(0,bField);
}

AliTPCExBFirst::AliTPCExBFirst(const AliFieldMap *bFieldMap,
			       Double_t driftVelocity) 
  : fDriftVelocity(driftVelocity),
    fkNX(0),fkNY(0),fkNZ(0),
    fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
    fkZMin(-250.),fkZMax(250.),
    fkNMean(0),
    fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
  //
  // The constructor. One has to supply a field map and an (initial)
  // drift velocity.
  //

  fkXMin=bFieldMap->Xmin()
    -TMath::Ceil( (bFieldMap->Xmin()+250.0)/bFieldMap->DelX())
    *bFieldMap->DelX();
  fkXMax=bFieldMap->Xmax()
    -TMath::Floor((bFieldMap->Xmax()-250.0)/bFieldMap->DelX())
    *bFieldMap->DelX();
  fkYMin=bFieldMap->Ymin()
    -TMath::Ceil( (bFieldMap->Ymin()+250.0)/bFieldMap->DelY())
    *bFieldMap->DelY();
  fkYMax=bFieldMap->Ymax()
    -TMath::Floor((bFieldMap->Ymax()-250.0)/bFieldMap->DelY())
    *bFieldMap->DelY();
  fkZMin=bFieldMap->Zmin()
    -TMath::Ceil( (bFieldMap->Zmin()+250.0)/bFieldMap->DelZ())
    *bFieldMap->DelZ();
  fkZMax=bFieldMap->Zmax()
    -TMath::Floor((bFieldMap->Zmax()-250.0)/bFieldMap->DelZ())
    *bFieldMap->DelZ();

  fkNX=static_cast<Int_t>((fkXMax-fkXMin)/bFieldMap->DelX()+1.1);
  fkNY=static_cast<Int_t>((fkYMax-fkYMin)/bFieldMap->DelY()+1.1);
  fkNZ=static_cast<Int_t>((fkZMax-fkZMin)/bFieldMap->DelZ()+1.1);

  ConstructCommon(bFieldMap,0);
}

AliTPCExBFirst::~AliTPCExBFirst() { 
  //
  // destruct the poor object.
  //
  delete[] fkMeanBx;
  delete[] fkMeanBy;
}

void AliTPCExBFirst::Correct(const Double_t *position,Double_t *corrected) {
  //
  // correct for the distortion
  //
  Double_t bx,by;
  GetMeanFields(position[0],position[1],position[2],&bx,&by);
  if (position[2]>0.) {
    Double_t bxe,bye;
    GetMeanFields(position[0],position[1],250.,&bxe,&bye);
    if (position[2]!=250.) {
      bx=(500.*bxe-(position[2]+250.)*bx)/(250.-position[2]);
      by=(500.*bye-(position[2]+250.)*by)/(250.-position[2]);
    }
    else {
      bx=bxe;
      by=bye;
    }
  }
  
  Double_t mu=fDriftVelocity/fgkDriftField;
  Double_t wt=mu*fkMeanBz;
  
  corrected[0]=mu*(wt*bx-by)/(1.+wt*wt);
  corrected[1]=mu*(wt*by+bx)/(1.+wt*wt);
  
  if (position[2]>0.) {
    corrected[0]*=(250.-position[2]);
    corrected[1]*=(250.-position[2]);
  }
  else {
    corrected[0]*=(-250.-position[2]);
    corrected[1]*=(-250.-position[2]);
  }

  corrected[0]=position[0]-corrected[0];
  corrected[1]=position[1]-corrected[1];
  corrected[2]=position[2];
}

void AliTPCExBFirst::TestThisBeautifulObject(const char* fileName) {
  //
  // well, as the name sais...
  //
  TTreeSRedirector ts(fileName);
  Double_t x[3];
  for (x[0]=-250.;x[0]<=250.;x[0]+=10.)
    for (x[1]=-250.;x[1]<=250.;x[1]+=10.)
      for (x[2]=-250.;x[2]<=250.;x[2]+=10.) {
	Double_t d[3];
	Correct(x,d);
	Double_t r=TMath::Sqrt(x[0]*x[0]+x[1]*x[1]);
	Double_t rd=TMath::Sqrt(d[0]*d[0]+d[1]*d[1]);
	Double_t dr=r-rd;
	Double_t phi=TMath::ATan2(x[0],x[1]);
	Double_t phid=TMath::ATan2(d[0],d[1]);
	Double_t dphi=phi-phid;
	if (dphi<0.) dphi+=TMath::TwoPi();
	if (dphi>TMath::Pi()) dphi=TMath::TwoPi()-dphi;
	Double_t drphi=r*dphi;
	Double_t dx=x[0]-d[0];
	Double_t dy=x[1]-d[1];
	Double_t dz=x[2]-d[2];
	ts<<"positions"
	  <<"x0="<<x[0]
	  <<"x1="<<x[1]
	  <<"x2="<<x[2]
	  <<"dx="<<dx
	  <<"dy="<<dy
	  <<"dz="<<dz
	  <<"r="<<r
	  <<"phi="<<phi
	  <<"dr="<<dr
	  <<"drphi="<<drphi
	  <<"\n";
      }
}

void AliTPCExBFirst::ConstructCommon(const AliFieldMap *bFieldMap,
				     const AliMagF *bField) {
  //
  // THIS IS PRIVATE! (a helper for the constructor)
  //
  fkNMean=fkNX*fkNY*fkNZ;
  fkMeanBx=new Double_t[fkNMean];
  fkMeanBy=new Double_t[fkNMean];

  Double_t x[3];
  Double_t nBz=0;
  fkMeanBz=0.;
  for (int i=0;i<fkNX;++i) {
    x[0]=fkXMin+i*(fkXMax-fkXMin)/(fkNX-1);
    for (int j=0;j<fkNY;++j) {
      x[1]=fkYMin+j*(fkYMax-fkYMin)/(fkNY-1);
      Double_t r=TMath::Sqrt(x[0]*x[0]+x[1]*x[1]);
      Double_t bx=0.,by=0.;
      for (int k=0;k<fkNZ;++k) {
	x[2]=fkZMin+k*(fkZMax-fkZMin)/(fkNZ-1);
	Float_t b[3];
	// the x is not const in the Field function...
	Float_t xt[3];
	for (int l=0;l<3;++l) xt[l]=x[l];
	// that happens due to the lack of a sophisticated class design:
	if (bFieldMap!=0)
	  bFieldMap->Field(xt,b);
	else 
	  bField->Field(xt,b);
	bx+=b[0]/10.;
	by+=b[1]/10.;
	fkMeanBx[(k*fkNY+j)*fkNX+i]=bx;
	fkMeanBy[(k*fkNY+j)*fkNX+i]=by;
	if (90.<=r&&r<=250.) {
	  fkMeanBz+=b[2]/10.;
	  ++nBz;
	}
      }
    }
  }
  fkMeanBz/=nBz;
}

void AliTPCExBFirst::GetMeanFields(Double_t rx,Double_t ry,Double_t rz,
				   Double_t *Bx,Double_t *By) const {
  //
  // THIS IS PRIVATE! (calculates the mean field utilising a lookup table)
  //
  Double_t x=(fkNX-1)*(rx-fkXMin)/(fkXMax-fkXMin);
  Int_t xi1=static_cast<Int_t>(x);
  xi1=TMath::Max(TMath::Min(xi1,fkNX-2),0);
  Int_t xi2=xi1+1;
  Double_t dx=(x-xi1);
  Double_t dx1=(xi2-x);

  Double_t y=(fkNY-1)*(ry-fkYMin)/(fkYMax-fkYMin);
  Int_t yi1=static_cast<Int_t>(y);
  yi1=TMath::Max(TMath::Min(yi1,fkNY-2),0);
  Int_t yi2=yi1+1;
  Double_t dy=(y-yi1);
  Double_t dy1=(yi2-y);
  
  Double_t z=(fkNZ-1)*(rz-fkZMin)/(fkZMax-fkZMin);
  Int_t zi1=static_cast<Int_t>(z);
  zi1=TMath::Max(TMath::Min(zi1,fkNZ-2),0);
  Int_t zi2=zi1+1;
  Double_t dz=(z-zi1);

  double s0x=fkMeanBx[yi1*fkNX+xi1]*dx1*dy1
	    +fkMeanBx[yi2*fkNX+xi1]*dx1*dy
            +fkMeanBx[yi1*fkNX+xi2]*dx *dy
            +fkMeanBx[yi2*fkNX+xi2]*dx *dy1;
  double s0y=fkMeanBy[yi1*fkNX+xi1]*dx1*dy1
	    +fkMeanBy[yi2*fkNX+xi1]*dx1*dy
            +fkMeanBy[yi1*fkNX+xi2]*dx *dy
            +fkMeanBy[yi2*fkNX+xi2]*dx *dy1;
  Int_t zi0=zi1-1;
  double snmx,snmy;
  if (zi0>=0) {
    snmx=fkMeanBx[(zi0*fkNY+yi1)*fkNX+xi1]*dx1*dy1
        +fkMeanBx[(zi0*fkNY+yi2)*fkNX+xi1]*dx1*dy
        +fkMeanBx[(zi0*fkNY+yi1)*fkNX+xi2]*dx *dy
        +fkMeanBx[(zi0*fkNY+yi2)*fkNX+xi2]*dx *dy1;
    snmy=fkMeanBy[(zi0*fkNY+yi1)*fkNX+xi1]*dx1*dy1
        +fkMeanBy[(zi0*fkNY+yi2)*fkNX+xi1]*dx1*dy
        +fkMeanBy[(zi0*fkNY+yi1)*fkNX+xi2]*dx *dy
        +fkMeanBy[(zi0*fkNY+yi2)*fkNX+xi2]*dx *dy1;
  }
  else
    snmx=snmy=0.;
  double snx=fkMeanBx[(zi1*fkNY+yi1)*fkNX+xi1]*dx1*dy1
 	    +fkMeanBx[(zi1*fkNY+yi2)*fkNX+xi1]*dx1*dy
            +fkMeanBx[(zi1*fkNY+yi1)*fkNX+xi2]*dx *dy
            +fkMeanBx[(zi1*fkNY+yi2)*fkNX+xi2]*dx *dy1;
  double sny=fkMeanBy[(zi1*fkNY+yi1)*fkNX+xi1]*dx1*dy1
 	    +fkMeanBy[(zi1*fkNY+yi2)*fkNX+xi1]*dx1*dy
            +fkMeanBy[(zi1*fkNY+yi1)*fkNX+xi2]*dx *dy
            +fkMeanBy[(zi1*fkNY+yi2)*fkNX+xi2]*dx *dy1;
  double snpx=fkMeanBx[(zi2*fkNY+yi1)*fkNX+xi1]*dx1*dy1
	     +fkMeanBx[(zi2*fkNY+yi2)*fkNX+xi1]*dx1*dy
             +fkMeanBx[(zi2*fkNY+yi1)*fkNX+xi2]*dx *dy
             +fkMeanBx[(zi2*fkNY+yi2)*fkNX+xi2]*dx *dy1;
  double snpy=fkMeanBy[(zi2*fkNY+yi1)*fkNX+xi1]*dx1*dy1
	     +fkMeanBy[(zi2*fkNY+yi2)*fkNX+xi1]*dx1*dy
             +fkMeanBy[(zi2*fkNY+yi1)*fkNX+xi2]*dx *dy
             +fkMeanBy[(zi2*fkNY+yi2)*fkNX+xi2]*dx *dy1;
  *Bx=0.5*(((snpx-2.*snx+snmx)*dz+2.*(snx-snmx))*dz+snx-s0x+snmx);
  *By=0.5*(((snpy-2.*sny+snmy)*dz+2.*(sny-snmy))*dz+sny-s0y+snmy);
  //TODO: make this nice
  if (TMath::Abs(z)>0.001) {
    *Bx/=z;
    *By/=z;
  }
}
Commit	Line	Data
cf585711	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	////
	17	// This implementation AliTPCExB is using an aproximate calculation of the ExB
	18	// effect. Therefore the drift ODE is Taylor expanded and only the first
	19	// order part is taken.
	20	////
	21
faf93237	22	#include "TMath.h"
cf585711	23	#include "AliFieldMap.h"
cf585711	24	#include "AliMagF.h"
faf93237	25	#include "TTreeStream.h"
	26	#include "AliTPCExBFirst.h"
	27
	28	ClassImp(AliTPCExBFirst)
	29
	30	const Double_t AliTPCExBFirst::fgkEM=1.602176487e-19/9.10938215e-31;
	31	const Double_t AliTPCExBFirst::fgkDriftField=40.e3;
	32
481f877b	33	AliTPCExBFirst::AliTPCExBFirst()
	34	: fDriftVelocity(0),
	35	fkNX(0),fkNY(0),fkNZ(0),
	36	fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
	37	fkZMin(-250.),fkZMax(250.),
	38	fkNMean(0),
	39	fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
	40	//
	41	// purely for I/O
	42	//
	43	}
	44
faf93237	45	AliTPCExBFirst::AliTPCExBFirst(const AliMagF *bField,
	46	Double_t driftVelocity,
	47	Int_t nx,Int_t ny,Int_t nz)
481f877b	48	: fDriftVelocity(driftVelocity),
481f877b	49	fkNX(nx),fkNY(ny),fkNZ(nz),
faf93237	50	fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
481f877b	51	fkZMin(-250.),fkZMax(250.),
	52	fkNMean(0),
	53	fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
faf93237	54	//
	55	// The constructor. One has to supply a magnetic field and an (initial)
	56	// drift velocity. Since some kind of lookuptable is created the
	57	// number of its meshpoints can be supplied.
	58	//
faf93237	59	ConstructCommon(0,bField);
	60	}
	61
	62	AliTPCExBFirst::AliTPCExBFirst(const AliFieldMap *bFieldMap,
481f877b	63	Double_t driftVelocity)
	64	: fDriftVelocity(driftVelocity),
	65	fkNX(0),fkNY(0),fkNZ(0),
	66	fkXMin(-250.),fkXMax(250.),fkYMin(-250.),fkYMax(250.),
	67	fkZMin(-250.),fkZMax(250.),
	68	fkNMean(0),
	69	fkMeanBx(0),fkMeanBy(0),fkMeanBz(0.) {
faf93237	70	//
	71	// The constructor. One has to supply a field map and an (initial)
	72	// drift velocity.
	73	//
faf93237	74
	75	fkXMin=bFieldMap->Xmin()
	76	-TMath::Ceil( (bFieldMap->Xmin()+250.0)/bFieldMap->DelX())
	77	*bFieldMap->DelX();
	78	fkXMax=bFieldMap->Xmax()
	79	-TMath::Floor((bFieldMap->Xmax()-250.0)/bFieldMap->DelX())
	80	*bFieldMap->DelX();
	81	fkYMin=bFieldMap->Ymin()
	82	-TMath::Ceil( (bFieldMap->Ymin()+250.0)/bFieldMap->DelY())
	83	*bFieldMap->DelY();
	84	fkYMax=bFieldMap->Ymax()
	85	-TMath::Floor((bFieldMap->Ymax()-250.0)/bFieldMap->DelY())
	86	*bFieldMap->DelY();
	87	fkZMin=bFieldMap->Zmin()
	88	-TMath::Ceil( (bFieldMap->Zmin()+250.0)/bFieldMap->DelZ())
	89	*bFieldMap->DelZ();
	90	fkZMax=bFieldMap->Zmax()
	91	-TMath::Floor((bFieldMap->Zmax()-250.0)/bFieldMap->DelZ())
	92	*bFieldMap->DelZ();
	93
	94	fkNX=static_cast<Int_t>((fkXMax-fkXMin)/bFieldMap->DelX()+1.1);
	95	fkNY=static_cast<Int_t>((fkYMax-fkYMin)/bFieldMap->DelY()+1.1);
	96	fkNZ=static_cast<Int_t>((fkZMax-fkZMin)/bFieldMap->DelZ()+1.1);
	97
	98	ConstructCommon(bFieldMap,0);
	99	}
	100
	101	AliTPCExBFirst::~AliTPCExBFirst() {
	102	//
	103	// destruct the poor object.
	104	//
481f877b	105	delete[] fkMeanBx;
481f877b	106	delete[] fkMeanBy;
faf93237	107	}
	108
	109	void AliTPCExBFirst::Correct(const Double_t position,Double_t corrected) {
	110	//
	111	// correct for the distortion
	112	//
cf585711	113	Double_t bx,by;
cf585711	114	GetMeanFields(position[0],position[1],position[2],&bx,&by);
481f877b	115	if (position[2]>0.) {
cf585711	116	Double_t bxe,bye;
cf585711	117	GetMeanFields(position[0],position[1],250.,&bxe,&bye);
481f877b	118	if (position[2]!=250.) {
cf585711	119	bx=(500.bxe-(position[2]+250.)bx)/(250.-position[2]);
cf585711	120	by=(500.bye-(position[2]+250.)by)/(250.-position[2]);
faf93237	121	}
faf93237	122	else {
cf585711	123	bx=bxe;
cf585711	124	by=bye;
faf93237	125	}
faf93237	126	}
481f877b	127
	128	Double_t mu=fDriftVelocity/fgkDriftField;
	129	Double_t wt=mu*fkMeanBz;
	130
cf585711	131	corrected[0]=mu(wtbx-by)/(1.+wt*wt);
cf585711	132	corrected[1]=mu(wtby+bx)/(1.+wt*wt);
481f877b	133
	134	if (position[2]>0.) {
	135	corrected[0]*=(250.-position[2]);
	136	corrected[1]*=(250.-position[2]);
	137	}
	138	else {
	139	corrected[0]*=(-250.-position[2]);
	140	corrected[1]*=(-250.-position[2]);
	141	}
	142
	143	corrected[0]=position[0]-corrected[0];
	144	corrected[1]=position[1]-corrected[1];
	145	corrected[2]=position[2];
faf93237	146	}
	147
	148	void AliTPCExBFirst::TestThisBeautifulObject(const char* fileName) {
	149	//
	150	// well, as the name sais...
	151	//
	152	TTreeSRedirector ts(fileName);
	153	Double_t x[3];
	154	for (x[0]=-250.;x[0]<=250.;x[0]+=10.)
	155	for (x[1]=-250.;x[1]<=250.;x[1]+=10.)
	156	for (x[2]=-250.;x[2]<=250.;x[2]+=10.) {
	157	Double_t d[3];
	158	Correct(x,d);
	159	Double_t r=TMath::Sqrt(x[0]x[0]+x[1]x[1]);
	160	Double_t rd=TMath::Sqrt(d[0]d[0]+d[1]d[1]);
	161	Double_t dr=r-rd;
	162	Double_t phi=TMath::ATan2(x[0],x[1]);
	163	Double_t phid=TMath::ATan2(d[0],d[1]);
	164	Double_t dphi=phi-phid;
	165	if (dphi<0.) dphi+=TMath::TwoPi();
	166	if (dphi>TMath::Pi()) dphi=TMath::TwoPi()-dphi;
	167	Double_t drphi=r*dphi;
	168	Double_t dx=x[0]-d[0];
	169	Double_t dy=x[1]-d[1];
	170	Double_t dz=x[2]-d[2];
	171	ts<<"positions"
	172	<<"x0="<<x[0]
	173	<<"x1="<<x[1]
	174	<<"x2="<<x[2]
	175	<<"dx="<<dx
	176	<<"dy="<<dy
	177	<<"dz="<<dz
	178	<<"r="<<r
	179	<<"phi="<<phi
	180	<<"dr="<<dr
	181	<<"drphi="<<drphi
	182	<<"\n";
	183	}
	184	}
	185
	186	void AliTPCExBFirst::ConstructCommon(const AliFieldMap *bFieldMap,
	187	const AliMagF *bField) {
	188	//
	189	// THIS IS PRIVATE! (a helper for the constructor)
	190	//
481f877b	191	fkNMean=fkNXfkNYfkNZ;
cf585711	192	fkMeanBx=new Double_t[fkNMean];
cf585711	193	fkMeanBy=new Double_t[fkNMean];
faf93237	194
	195	Double_t x[3];
	196	Double_t nBz=0;
481f877b	197	fkMeanBz=0.;
faf93237	198	for (int i=0;i<fkNX;++i) {
	199	x[0]=fkXMin+i*(fkXMax-fkXMin)/(fkNX-1);
	200	for (int j=0;j<fkNY;++j) {
	201	x[1]=fkYMin+j*(fkYMax-fkYMin)/(fkNY-1);
cf585711	202	Double_t r=TMath::Sqrt(x[0]x[0]+x[1]x[1]);
cf585711	203	Double_t bx=0.,by=0.;
faf93237	204	for (int k=0;k<fkNZ;++k) {
faf93237	205	x[2]=fkZMin+k*(fkZMax-fkZMin)/(fkNZ-1);
cf585711	206	Float_t b[3];
faf93237	207	// the x is not const in the Field function...
	208	Float_t xt[3];
	209	for (int l=0;l<3;++l) xt[l]=x[l];
	210	// that happens due to the lack of a sophisticated class design:
	211	if (bFieldMap!=0)
cf585711	212	bFieldMap->Field(xt,b);
faf93237	213	else
cf585711	214	bField->Field(xt,b);
	215	bx+=b[0]/10.;
	216	by+=b[1]/10.;
	217	fkMeanBx[(kfkNY+j)fkNX+i]=bx;
	218	fkMeanBy[(kfkNY+j)fkNX+i]=by;
	219	if (90.<=r&&r<=250.) {
	220	fkMeanBz+=b[2]/10.;
faf93237	221	++nBz;
	222	}
	223	}
	224	}
	225	}
481f877b	226	fkMeanBz/=nBz;
faf93237	227	}
	228
	229	void AliTPCExBFirst::GetMeanFields(Double_t rx,Double_t ry,Double_t rz,
	230	Double_t Bx,Double_t By) const {
	231	//
	232	// THIS IS PRIVATE! (calculates the mean field utilising a lookup table)
	233	//
	234	Double_t x=(fkNX-1)*(rx-fkXMin)/(fkXMax-fkXMin);
	235	Int_t xi1=static_cast<Int_t>(x);
	236	xi1=TMath::Max(TMath::Min(xi1,fkNX-2),0);
	237	Int_t xi2=xi1+1;
	238	Double_t dx=(x-xi1);
	239	Double_t dx1=(xi2-x);
	240
	241	Double_t y=(fkNY-1)*(ry-fkYMin)/(fkYMax-fkYMin);
	242	Int_t yi1=static_cast<Int_t>(y);
	243	yi1=TMath::Max(TMath::Min(yi1,fkNY-2),0);
	244	Int_t yi2=yi1+1;
	245	Double_t dy=(y-yi1);
	246	Double_t dy1=(yi2-y);
	247
	248	Double_t z=(fkNZ-1)*(rz-fkZMin)/(fkZMax-fkZMin);
	249	Int_t zi1=static_cast<Int_t>(z);
	250	zi1=TMath::Max(TMath::Min(zi1,fkNZ-2),0);
	251	Int_t zi2=zi1+1;
	252	Double_t dz=(z-zi1);
	253
481f877b	254	double s0x=fkMeanBx[yi1fkNX+xi1]dx1*dy1
	255	+fkMeanBx[yi2fkNX+xi1]dx1*dy
	256	+fkMeanBx[yi1fkNX+xi2]dx *dy
	257	+fkMeanBx[yi2fkNX+xi2]dx *dy1;
	258	double s0y=fkMeanBy[yi1fkNX+xi1]dx1*dy1
	259	+fkMeanBy[yi2fkNX+xi1]dx1*dy
	260	+fkMeanBy[yi1fkNX+xi2]dx *dy
	261	+fkMeanBy[yi2fkNX+xi2]dx *dy1;
faf93237	262	Int_t zi0=zi1-1;
	263	double snmx,snmy;
	264	if (zi0>=0) {
481f877b	265	snmx=fkMeanBx[(zi0fkNY+yi1)fkNX+xi1]dx1dy1
	266	+fkMeanBx[(zi0fkNY+yi2)fkNX+xi1]dx1dy
	267	+fkMeanBx[(zi0fkNY+yi1)fkNX+xi2]dx dy
	268	+fkMeanBx[(zi0fkNY+yi2)fkNX+xi2]dx dy1;
	269	snmy=fkMeanBy[(zi0fkNY+yi1)fkNX+xi1]dx1dy1
	270	+fkMeanBy[(zi0fkNY+yi2)fkNX+xi1]dx1dy
	271	+fkMeanBy[(zi0fkNY+yi1)fkNX+xi2]dx dy
	272	+fkMeanBy[(zi0fkNY+yi2)fkNX+xi2]dx dy1;
faf93237	273	}
	274	else
	275	snmx=snmy=0.;
481f877b	276	double snx=fkMeanBx[(zi1fkNY+yi1)fkNX+xi1]dx1dy1
	277	+fkMeanBx[(zi1fkNY+yi2)fkNX+xi1]dx1dy
	278	+fkMeanBx[(zi1fkNY+yi1)fkNX+xi2]dx dy
	279	+fkMeanBx[(zi1fkNY+yi2)fkNX+xi2]dx dy1;
	280	double sny=fkMeanBy[(zi1fkNY+yi1)fkNX+xi1]dx1dy1
	281	+fkMeanBy[(zi1fkNY+yi2)fkNX+xi1]dx1dy
	282	+fkMeanBy[(zi1fkNY+yi1)fkNX+xi2]dx dy
	283	+fkMeanBy[(zi1fkNY+yi2)fkNX+xi2]dx dy1;
	284	double snpx=fkMeanBx[(zi2fkNY+yi1)fkNX+xi1]dx1dy1
	285	+fkMeanBx[(zi2fkNY+yi2)fkNX+xi1]dx1dy
	286	+fkMeanBx[(zi2fkNY+yi1)fkNX+xi2]dx dy
	287	+fkMeanBx[(zi2fkNY+yi2)fkNX+xi2]dx dy1;
	288	double snpy=fkMeanBy[(zi2fkNY+yi1)fkNX+xi1]dx1dy1
	289	+fkMeanBy[(zi2fkNY+yi2)fkNX+xi1]dx1dy
	290	+fkMeanBy[(zi2fkNY+yi1)fkNX+xi2]dx dy
	291	+fkMeanBy[(zi2fkNY+yi2)fkNX+xi2]dx dy1;
faf93237	292	Bx=0.5(((snpx-2.snx+snmx)dz+2.(snx-snmx))dz+snx-s0x+snmx);
	293	By=0.5(((snpy-2.sny+snmy)dz+2.(sny-snmy))dz+sny-s0y+snmy);
	294	//TODO: make this nice
	295	if (TMath::Abs(z)>0.001) {
	296	*Bx/=z;
	297	*By/=z;
	298	}
	299	}