#include <TRandom2.h>
#include <TCanvas.h>
#include <TF1.h>

//function and initial points
Double_t func(Double_t x) {
  return x*0.5+sin(x);
}

// histograms filled and drawn in a loop
void zlatirez() {

  TCanvas *c1 = new TCanvas("c1","Zlati rez",200,10,600,600);
  c1->SetGrid();

  Double_t ax,bx,cx,xmin,fmin;
  xmin=-1e8;
  ax=-4.;
  bx=0;
  cx=1;
  // Create some histograms.
  TF1* main   = new TF1("MyFunc","func(x)",-5.,5.);
  main->SetFillColor(41);
  main->SetNpx(100000);
 

  // Fill histograms 
  const Int_t niter=10000;
  Double_t wgold=(3.-sqrt(5.))*0.5;
  Double_t r=1-wgold;
  Double_t epsilon=1e-3;
  Double_t x[niter], y[niter];
  

  Double_t f1,f2,x0,x1,x2,x3;
  x0=ax;
  x3=cx;
  //wider interval
  if (fabs(cx-bx) > fabs(bx-ax)) {
    x1=bx;
    x2=bx+wgold*(cx-bx);
  } else {
    x2=bx;
    x1=bx-wgold*(bx-ax);
  }
  f1=func(x1);
  f2=func(x2);
  Int_t  i=0;
  for ( i=0; i<niter; i++) {
    if (fabs(x3-x0) < epsilon*(fabs(x1)+fabs(x2))) { break; }


    f1=func(x1);
    f2=func(x2);
    if (f2 < f1) {
      x0=x1;
      x1=x2;
      x2=x1+wgold*(x3-x1);
      f1=f2;
      f2=func(x2);
      x[i]=x2;
      y[i]=f2;
    } else {
      x3=x2;
      x2=x1;
      x1=x2+wgold*(x0-x2);
      f2=f1;
      f1=func(x1);
      x[i]=x1;
      y[i]=f1;
    }    
    //std::cout << x << ' ' << y << std::endl;
  }

  std::cout << "iter done=" << i << " niter=" << niter << std::endl;
  main->Draw();

  if (f1 < f2) {
    xmin=x1;
    fmin=f1;
  } else {
    xmin=x2;
    fmin=f2;
  }


  x[i]=ax;
  y[i]=func(ax);
  x[i+1]=bx;
  y[i+1]=func(bx);
  x[i+2]=cx;
  y[i+2]=func(cx);

  const Int_t itgraph=i+3;

  for (Int_t j=0; j< itgraph; j++) {
    std::cout << "j=" << j << " x=" << x[j] << " y=" << y[j] << std::endl;
  }

  std::cout << "xmin=" << xmin << " func(xmin)=" << fmin << std::endl;

  gr = new TGraph(itgraph,x,y);

  //point overlay
  gr->SetLineColor(1);
  gr->SetLineWidth(1);
  gr->SetMarkerColor(4);
  gr->SetMarkerStyle(21);
  gr->Draw("P"); 


  c1->Update();
  c1->Modified();
}