python_example2.py

#!/usr/bin/env python3
import ROOT as r, sys, math
r.gROOT.SetBatch(True)
r.TH1.AddDirectory(False)

def H(n,t):
    h = r.TH2F(n,t,100,50,150,100,50,150)
    h.SetDirectory(0)
    return h

def python_example2(samples=10000):
    rng = r.TRandom3()
    h1 = H("h1","2D Gaussian;x;y")
    for _ in range(samples):
        x = rng.Gaus(100,6); y = rng.Gaus(100,6)
        if 50<=x<=150 and 50<=y<=150: h1.Fill(x,y)

    h2 = H("h2","2D Gaussian + uniform;x;y"); h2.Add(h1)
    for _ in range(samples//3):
        h2.Fill(rng.Uniform(50,150), rng.Uniform(50,150))

    h3 = H("h3","2D Gaussian + 1/r^2;x;y"); h3.Add(h1)
    for _ in range(samples*10):
        u = rng.Uniform(0,1-1.0/11.0); rrad = 1.0/(1.0-u); th = rng.Uniform(0,2*math.pi)
        x = 100 + 10*rrad*math.cos(th); y = 100 + 10*rrad*math.sin(th)
        if 50<=x<=150 and 50<=y<=150: h3.Fill(x,y)

    h4 = H("h4","Mixture of 2D Gaussians;x;y"); h4.Add(h1)
    for _ in range(samples//2):
        x = rng.Gaus(100,20); y = rng.Gaus(100,20)
        if 50<=x<=150 and 50<=y<=150: h4.Fill(x,y)

    c = r.TCanvas("c2d_py","Canvas2D_py",900,900)
    c.Divide(2,2)
    c.cd(1); h1.Draw("COLZ")
    c.cd(2); h2.Draw("COLZ")
    c.cd(3); h3.Draw("COLZ")
    c.cd(4); h4.Draw("COLZ")
    c.SaveAs("canvas2d_py.png")

if __name__=="__main__":
    n = int(sys.argv[1]) if len(sys.argv)>1 else 10000
    python_example2(n)