double lin(double* x, double* p)
{
	return p[0] + x[0] * p[1];
}

void upf_cv11_fit(const char* fileName)
{
	FILE* file = fopen(fileName,"r");
	int N = 0;
	double x, y, sigma;

	TGraphErrors* gr = new TGraphErrors();	// objekt grafu s chybovymi useckami

	// dokud prectes 3 cisla, prochazej radky...
	while(fscanf(file,"%lf %lf %lf", &x, &y, &sigma) == 3)
	{
		gr->SetPoint(N, x, y);				// nastav x a y N-teho bodu
		gr->SetPointError(N, 0, sigma);		// nastav jeho sigma_x a sigma_y
		N++;		// pocitadlo radku
	}
	printf("Precten soubor '%s' s %i radky.\n",fileName,N);
	fclose(file);	// zavri soubor

	gr->SetMarkerStyle(8);
	gr->SetMarkerColor(1);
	gr->Draw("PA");

	// definuj funkci:
/*	TF1* func = new TF1("func","[0] + [1]*x", 		// [i] je i-ty parametr
				gr->GetX()[0], gr->GetX()[N-1]);	// gr->GetX() je pole x
	func->SetParameters(0,0);	// nastav pocatecni hodnoty
*/
	// konstrukce s ukazatelem na C++ funkci:
	TF1* func = new TF1("func",&lin,gr->GetX()[0], gr->GetX()[N-1],2);

/*	TF1* func = new TF1("func","[0] + [1]*sin(x) + [2]*cos(x) + [3]*sin(2*x) + [4]*cos(2*x)", 		// [i] je i-ty parametr
				gr->GetX()[0], gr->GetX()[N-1]);	// gr->GetX() je pole x
	func->SetParameters(0,0,0,0,0);	// nastav pocatecni hodnoty
*/

	TFitResultPtr res = gr->Fit(func,"S");

	printf("\nNafitovane parametry: %.4f +/- %.4f  %.4f +/- %.4f\n",
		func->GetParameter(0),func->GetParError(0),
		func->GetParameter(1),func->GetParError(1));

	printf("\n Matice kovariance:\n");
	for (int i = 0; i < func->GetNpar(); i++)
	{
		for (int j = 0; j < func->GetNpar(); j++)
			printf(" %7.3f", res->CovMatrix(i,j));
		printf("\n");
	}

	printf("\n Matice korelace:\n");
	for (int i = 0; i < func->GetNpar(); i++)
	{
		for (int j = 0; j < func->GetNpar(); j++)
			printf(" %7.3f", res->CovMatrix(i,j) / sqrt(res->CovMatrix(i,i))
					 / sqrt(res->CovMatrix(j,j)));
		printf("\n");
	}
}