# Spherical Random Numbers

    #include "TRandom.h"
    #include "TCanvas.h"
    #include "TView.h"
    #include "TPolyMarker3D.h"

    void spheres(Int_t nspheres=20, Int_t npoints=100000) {
       // generate random points uniformly distributed over the surface
       // of spheres generated at random positions.

       TCanvas *c1 = new TCanvas("c1","spheres",600,600);
       c1->SetFillColor(kBlack);
       TView *view = new TView(1);
       Double_t k=0.8;
       view->SetRange( -k, -k, -k, k, k, k);

       //generate sphere coordinates and radius
       TRandom r;
       if (nspheres <=0) nspheres = 10;
       Double_t *xs = new Double_t[nspheres];
       Double_t *ys = new Double_t[nspheres];
       Double_t *zs = new Double_t[nspheres];
       Double_t *rs = new Double_t[nspheres];
       Int_t i;
       for (i=0;i<nspheres;i++) {
          xs[i] = r.Uniform(-1,1);
          ys[i] = r.Uniform(-1,1);
          zs[i] = r.Uniform(-1,1);
          rs[i] = r.Uniform(0.05,0.25);
       }

       //generate points
       TPolyMarker3D *pm = new TPolyMarker3D(npoints);
       pm->SetMarkerColor(kRed);
       Double_t x,y,z;
       for (Int_t j=0;j<npoints;j++) {
           i = (Int_t)r.Uniform(0,nspheres);  //choose sphere
           r.Sphere(x,y,z,rs[i]);
           pm->SetPoint(j,xs[i]+x, ys[i]+y,zs[i]+z);
       }

       delete [] xs;
       delete [] ys;
       delete [] zs;
       delete [] rs;

       pm->Draw();
    }