slits.C

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// Example drawing the interference pattern of light
// falling on a grid with n slits and ratio r of slit
// width over distance between slits.
 
auto pi = TMath::Pi();
 
// function code in C
double single(double *x, double *par) {
  return pow(sin(pi*par[0]*x[0])/(pi*par[0]*x[0]),2);
}
 
double nslit0(double *x,double *par){
  return pow(sin(pi*par[1]*x[0])/sin(pi*x[0]),2);
}
 
double nslit(double *x, double *par){
  return single(x,par) * nslit0(x,par);
}
 
// This is the main program
void slits() {
  float r,ns;
 
  // request user input
  cout << "slit width / g ? ";
  scanf("%f",&r);
  cout << "# of slits? ";
  scanf("%f",&ns);
  cout <<"interference pattern for "<< ns
       <<" slits, width/distance: "<<r<<endl;
 
  // define function and set options
  TF1 *Fnslit  = new TF1("Fnslit",nslit,-5.001,5.,2);
  Fnslit->SetNpx(500);
 
  // set parameters, as read in above
  Fnslit->SetParameter(0,r);
  Fnslit->SetParameter(1,ns);
 
  // draw the interference pattern for a grid with n slits
  Fnslit->Draw();
}