/* *** example to draw the interference pattern of light
falling on a grid with n slits
and ratio r of slit width over distance between slits ****/

/* func t i on code in C */
double single(double *x,double *par) {
double const pi=4*atan ( 1 . );
return pow(sin(pi*par[0]*x[0])/(pi*par[0]*x[0]),2); }

double nslit0(double *x,double *par) {
double const pi=4*atan(1.);
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 number of point s to 500

Fnslit->SetParameter (0,r); // set parameters, as read in above
Fnslit->SetParameter (1,ns);

Fnslit->Draw(); // draw the interference pattern for a grid with n slits
}