#include<iostream>
Double_t flux(Double_t* x, Double_t* par)   // define function 
{
Double_t E = x[0];
Double_t y = (par[0]*pow(10, -7)*pow(par[1], 0.78)*pow((E+par[2]),par[3]));
return y;
}
void roottut1()     // main function
{
TCanvas *c1 = new TCanvas();  //creating canvas
c1->SetLogy();            // set log scale
c1->SetLogx();
c1->SetGrid();           //set grid
TF1 *func = new TF1("func", "flux", 1, 100000,4);   // here 4 is number of parameters
//func->SetParameter( 0, 2.19596);
//func->SetParameter( 1, 1.51582500 );
//func->SetParameter(2, 938.00 );
//func->SetParameter(3, -3.05504);
func->SetParameters(2.19596,1.51582500,938.00,-3.05504);    
func->Draw();                                           
func->GetXaxis()->SetTitle("Energy (MeV/u)");
func->GetYaxis()->SetTitle("Differential Flux ( Particles/(m^{2}.s.sr.MeV/u) )");
func->SetTitle("LIS EQUATION");
func->GetXaxis()->SetTitleSize(0.04);
func->GetYaxis()->SetTitleSize(0.04);
func->GetXaxis()->SetLabelSize(0.05);
func->GetYaxis()->SetLabelSize(0.05);
func->GetXaxis()->SetTitleOffset(1.4);
func->GetYaxis()->SetTitleOffset(1.4); 
}