import ROOT

# Set up component pdfs
# ---------------------------------------

# Construct observable
t = ROOT.RooRealVar("t", "t", -10, 30)

# Construct landau(t,ml,sl)
ml = ROOT.RooRealVar("ml", "mean landau", 5.0, -20, 20)
sl = ROOT.RooRealVar("sl", "sigma landau", 1, 0.1, 10)
landau = ROOT.RooLandau("lx", "lx", t, ml, sl)

# Construct gauss(t,mg,sg)
mg = ROOT.RooRealVar("mg", "mg", 0)
sg = ROOT.RooRealVar("sg", "sg", 2, 0.1, 10)
gauss = ROOT.RooGaussian("gauss", "gauss", t, mg, sg)

# Construct convolution pdf
# ---------------------------------------

# Set #bins to be used for FFT sampling to 10000
t.setBins(10000, "cache")

# Construct landau (x) gauss
lxg = ROOT.RooFFTConvPdf("lxg", "landau (X) gauss", t, landau, gauss)

# Sample, fit and plot convoluted pdf
# ----------------------------------------------------------------------

# Sample 1000 events in x from gxlx
data = lxg.generate({t}, 10000)

# Fit gxlx to data
lxg.fitTo(data, PrintLevel=-1)

# Plot data, pdf, landau (X) gauss pdf
frame = t.frame(Title="landau (x) gauss convolution")
data.plotOn(frame)
lxg.plotOn(frame)
landau.plotOn(frame, LineStyle="--")

# Draw frame on canvas
c = ROOT.TCanvas("rf208_convolution", "rf208_convolution", 600, 600)
ROOT.gPad.SetLeftMargin(0.15)
frame.GetYaxis().SetTitleOffset(1.4)
frame.Draw()

c.SaveAs("rf208_convolution.png")