//generating functions converting channel into voltage,
//using file pksx.txt
//and save parameters into outputx.txt

void fitGr(const bool left,TGraphErrors *ger,char parout[30]){//fit & save graph of 0 & 2
	const short npol=5;
	char fcnform[10];
	sprintf(fcnform,"pol%d",npol);//form of fitting function
	TF1 *fcn=new TF1("",fcnform,0,4500.);
	fcn->SetParameter(0,-5e-2);
	fcn->SetParameter(1,1.e-3);
	if(npol>=2) fcn->SetParameter(2,-5.e-9);
	if(npol>=3) fcn->SetParameter(3, 0.);
	if(npol>=4) fcn->SetParameter(4, 0.);
	if(npol==5) fcn->SetParameter(5, 0.);

	if(left) ger->SetName("gl");//left side
	else if(!left) ger->SetName("gr");//right side

	gStyle->SetOptFit(0000);
	gStyle->SetOptStat(0);
	ger->Fit(fcn,"WQN"); // "initial pre-fit"
	ger->Fit(fcn,"EMQ+");//fit

	ofstream fout(parout,ios::app);
	if(left) fout<<"left ";
	else if(!left) fout<<"right ";
	for(short i=0;i<=npol;i++){
		fout<<fcn->GetParameter(i)<<"\t"<<fcn->GetParError(i);
		if(i<npol) fout<<" ";
	}
	fout<<endl;
	fout.close();
}

void ch2v_demo(){
	// read data from file
	const short ncol=16;
	short detID=-1;
	float x=0.,xerr=0.,y=0.,yerr=1.e-8;
	string line;
	char filein[15]="pksx.txt";
	ifstream fin(filein);
	cout<<"using file: "<<filein<<endl;
	TGraphErrors *gers[2][16];
	for(short i=0;i<2;i++) for(short j=0;j<16;j++) gers[i][j]=new TGraphErrors();

	const float thresholdl=70;
	const float thresholdr=60;
	getline(fin, line);//read the 1st line
	while(getline(fin, line)){
		stringstream ss(line);
		ss>>y>>detID>>detID>>x>>xerr;
		for(short i=0;i<ncol;i++){//left side
			if(x>thresholdl){
				gers[0][detID]->SetPoint(gers[0][detID]->GetN(),x,y);
				gers[0][detID]->SetPointError(gers[0][detID]->GetN()-1, xerr,yerr);
			}
			getline(fin, line);
			ss.clear();
			ss.str(line);
			ss>>y>>detID>>detID>>x>>xerr;
		}
		for(short i=0;i<ncol;i++){//right side
			if(x>thresholdr){
				gers[1][detID]->SetPoint(gers[1][detID]->GetN(),x,y);
				gers[1][detID]->SetPointError(gers[1][detID]->GetN()-1, xerr,yerr);
			}
			if(i==ncol-1) break;
			getline(fin, line);
			ss.clear();
			ss.str(line);
			ss>>y>>detID>>detID>>x>>xerr;
		}
	}
	fin.close();
	char parout[30]="outputx.txt";
	ofstream fout(parout);
	fout<<"Q = [0] + [1]*ch+..."<<endl;
	fout<<"par0\terr0\tpar1\terr1..."<<endl;
	fout.close();
	for(short i=0;i<ncol;i++){
		fitGr(true,gers[0][i],parout);//left side
		fitGr(false,gers[1][i],parout);//right side
	}
}