randomWalk_simple.C

//
//  randomWalk.C
////////////////////////////////////////////////////
//
//  Simple Monte Carlo
//
///////////////////////////////////////////////////
//  Created by @visionlib.postach.io
{
    const Int_t kIteration = 1000000;
    TFile *pfile = new TFile("randomWalk.root","RECREATE");
    TH1F *hx10 = new TH1F("hx10","",11,-0.5,10.5);
    TH1F *hy10 = new TH1F("hy10","",11,-0.5,10.5);
    
    TH1F *hx20 = new TH1F("hx20","",11,-0.5,10.5);
    TH1F *hy20 = new TH1F("hy20","",11,-0.5,10.5);
    
    TH1F *hstep = new TH1F("hstep","",100,0,500);
    TH2F *hstepvsdist = new TH2F("hstepvsdist","",163,-0.5,162.5,100,0,500);
    TH2F *hstepvsdistsqr = new TH2F("hstepvsdistsqr","",100,-0.5,13.5,100,0,500);
    //percentage
    TH1F *hstepLeft1 = new TH1F("hstepLeft1","",100,0,1);
    TH1F *hstepRight1 = new TH1F("hstepRight1","",100,0,1);
    TH1F *hstepUp1 = new TH1F("hstepUp1","",100,0,1);
    TH1F *hstepDown1 = new TH1F("hstepDown1","",100,0,1);
    
    TH1F *hstepLeft2 = new TH1F("hstepLeft2","",100,0,1);
    TH1F *hstepRight2 = new TH1F("hstepRight2","",100,0,1);
    TH1F *hstepUp2 = new TH1F("hstepUp2","",100,0,1);
    TH1F *hstepDown2 = new TH1F("hstepDown2","",100,0,1);
    int nleft1=0;
    int nright1=0;
    int nup1=0;
    int ndown1=0;
    
    int nleft2=0;
    int nright2=0;
    int nup2=0;
    int ndown2=0;
    
    for (Int_t i=0; i<kIteration;i++) {
        if (i%1000==0) printf("Processing %i/%i\n",i,kIteration);
        //Initialize position
        int trialstep=0;
        int x1 = (int)(gRandom->Uniform(0.0,1.0)*10);
        int y1 = (int)(gRandom->Uniform(0.0,1.0)*10);
        int x2 = (int)(gRandom->Uniform(0.0,1.0)*10);
        int y2 = (int)(gRandom->Uniform(0.0,1.0)*10);
        hx10->Fill(x1);
        hy10->Fill(y1);
        hx20->Fill(x2);
        hy20->Fill(y2);
        double chooseStep;
        int distant0 = (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
        nleft1=0;
        nright1=0;
        nup1=0;
        ndown1=0;
        nleft2=0;
        nright2=0;
        nup2=0;
        ndown2=0;
        while ((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) > 0) {
            
            trialstep +=1;
            //first person step in even step
            if (trialstep%2){
                    chooseStep = gRandom->Uniform(0.0,1.0);
                    if (chooseStep<0.25) {x1 = ((x1+1)%10);//step to right
                        nright1 +=1;
                    }
                    else if (chooseStep<0.5) {x1=(x1+9)%10; // step to left
                        nleft1 +=1;
                    }
                    else if (chooseStep<0.75) {y1=(y1+9)%10; // step down
                        ndown1 +=1;
                    }
                    else {y1=(y1+1)%10; // step up
                        nup1 +=1;
                    }
                
                
            }
            //second person step in odd step
            else {
                    chooseStep = gRandom->Uniform(0.0,1.0);
                    if (chooseStep<0.25) {x2 = ((x2+1)%10);//step to right
                        nright2 +=1;
                    }
                    else if (chooseStep<0.5) {x2=(x2+9)%10; // step to left
                        nleft2 +=1;
                    }
                    else if (chooseStep<0.75) {y2=(y2+9)%10; // step down
                        ndown2 +=1;
                    }
                    else {y2=(y2+1)%10; // step up
                        nup2 +=1;
                    }
                
                
            }//end else
        }//end while
        hstep->Fill(trialstep);
        hstepvsdist->Fill(distant0,trialstep);
        int nstep1 = nright1+nleft1+nup1+ndown1;
        int nstep2 = nright2+nleft2+nup2+ndown2;
        if(nstep1>0){
            hstepRight1->Fill(nright1*1.0/nstep1);
            hstepLeft1->Fill(nleft1*1.0/nstep1);
            hstepUp1->Fill(nup1*1.0/nstep1);
            hstepDown1->Fill(ndown1*1.0/nstep1);
        }
        if(nstep2>0){
            hstepRight2->Fill(nright2*1.0/nstep2);
            hstepLeft2->Fill(nleft2*1.0/nstep2);
            hstepUp2->Fill(nup2*1.0/nstep2);
            hstepDown2->Fill(ndown2*1.0/nstep2);
        }
    }//end for
    pfile->Write();
    pfile->Close();
    
}