Detailed Description

Convolution in cyclical angular observables theta, and construction of p.d.f in terms of transformed angular coordinates, e.g.

cos(theta), the convolution is performed in theta rather than cos(theta)

(require ROOT to be compiled with –enable-fftw3)

pdf(theta) = ROOT.T(theta) (x) gauss(theta) pdf(cosTheta) = ROOT.T(acos(cosTheta)) (x) gauss(acos(cosTheta))

 
import ROOT
 
# Set up component pdfs
# ---------------------------------------
 
# Define angle psi
psi = ROOT.RooRealVar("psi", "psi", 0, 3.14159268)
 
# Define physics p.d.f T(psi)
Tpsi = ROOT.RooGenericPdf("Tpsi", "1+sin(2*@0)", [psi])
 
# Define resolution R(psi)
gbias = ROOT.RooRealVar("gbias", "gbias", 0.2, 0.0, 1)
greso = ROOT.RooRealVar("greso", "greso", 0.3, 0.1, 1.0)
Rpsi = ROOT.RooGaussian("Rpsi", "Rpsi", psi, gbias, greso)
 
# Define cos(psi) and function psif that calculates psi from cos(psi)
cpsi = ROOT.RooRealVar("cpsi", "cos(psi)", -1, 1)
psif = ROOT.RooFormulaVar("psif", "acos(cpsi)", [cpsi])
 
# Define physics p.d.f. also as function of cos(psi): T(psif(cpsi)) = T(cpsi)
Tcpsi = ROOT.RooGenericPdf("T", "1+sin(2*@0)", [psif])
 
# Construct convolution pdf in psi
# --------------------------------------------------------------
 
# Define convoluted p.d.f. as function of psi: M=[T(x)R](psi) = M(psi)
Mpsi = ROOT.RooFFTConvPdf("Mf", "Mf", psi, Tpsi, Rpsi)
 
# Set the buffer fraction to zero to obtain a ROOT.True cyclical
# convolution
Mpsi.setBufferFraction(0)
 
# Sample, fit and plot convoluted pdf (psi)
# --------------------------------------------------------------------------------
 
# Generate some events in observable psi
data_psi = Mpsi.generate({psi}, 10000)
 
# Fit convoluted model as function of angle psi
Mpsi.fitTo(data_psi, PrintLevel=-1)
 
# Plot cos(psi) frame with Mf(cpsi)
frame1 = psi.frame(Title="Cyclical convolution in angle psi")
data_psi.plotOn(frame1)
Mpsi.plotOn(frame1)
 
# Overlay comparison to unsmeared physics p.d.f ROOT.T(psi)
Tpsi.plotOn(frame1, LineColor="r")
 
# Construct convolution pdf in cos(psi)
# --------------------------------------------------------------------------
 
# Define convoluted p.d.f. as function of cos(psi): M=[T(x)R](psif cpsi)) = M(cpsi:
#
# Need to give both observable psi here (for definition of convolution)
# and function psif here (for definition of observables, in cpsi)
Mcpsi = ROOT.RooFFTConvPdf("Mf", "Mf", psif, psi, Tpsi, Rpsi)
 
# Set the buffer fraction to zero to obtain a ROOT.True cyclical
# convolution
Mcpsi.setBufferFraction(0)
 
# Sample, fit and plot convoluted pdf (cospsi)
# --------------------------------------------------------------------------------
 
# Generate some events
data_cpsi = Mcpsi.generate({cpsi}, 10000)
 
# set psi constant to exclude to be a parameter of the fit
psi.setConstant(True)
 
# Fit convoluted model as function of cos(psi)
Mcpsi.fitTo(data_cpsi, PrintLevel=-1)
 
# Plot cos(psi) frame with Mf(cpsi)
frame2 = cpsi.frame(Title="Same convolution in psi, in cos(psi)")
data_cpsi.plotOn(frame2)
Mcpsi.plotOn(frame2)
 
# Overlay comparison to unsmeared physics p.d.f ROOT.Tf(cpsi)
Tcpsi.plotOn(frame2, LineColor="r")
 
# Draw frame on canvas
c = ROOT.TCanvas("rf210_angularconv", "rf210_angularconv", 800, 400)
c.Divide(2)
c.cd(1)
ROOT.gPad.SetLeftMargin(0.15)
frame1.GetYaxis().SetTitleOffset(1.4)
frame1.Draw()
c.cd(2)
ROOT.gPad.SetLeftMargin(0.15)
frame2.GetYaxis().SetTitleOffset(1.4)
frame2.Draw()
 
c.SaveAs("rf210_angularconv.png")

[#1] INFO:Caching -- Changing internal binning of variable 'psi' in FFT 'Mf' from 100 to 930 to improve the precision of the numerical FFT. This can be done manually by setting an additional binning named 'cache'.
[#1] INFO:Eval -- RooRealVar::setRange(psi) new range named 'refrange_fft_Mf' created with bounds [0,3.14159]
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087a04c440 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[psi]_NORM_psi for nset (psi) with code 0
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087a4d6ae0 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[psi]_NORM_psi for nset (psi) with code 0 from preexisting content.
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087a6c39e0 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[psi]_NORM_psi for nset (psi) with code 0 from preexisting content.
[#1] INFO:Fitting -- RooAbsPdf::fitTo(Mf_over_Mf_Int[psi]) fixing normalization set for coefficient determination to observables in data
[#1] INFO:Fitting -- using CPU computation library compiled with -mavx512
[#1] INFO:Fitting -- RooAddition::defaultErrorLevel(nll_Mf_over_Mf_Int[psi]_MfData) Summation contains a RooNLLVar, using its error level
[#1] INFO:Minimization -- RooAbsMinimizerFcn::setOptimizeConst: activating const optimization
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087a83e530 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[psi] for nset () with code 1 from preexisting content.
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Minimization -- RooAbsMinimizerFcn::setOptimizeConst: deactivating const optimization
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087ab022b0 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[psi]_NORM_psi for nset (psi) with code 0
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087aa41d20 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi for nset (cpsi) with code 0 from preexisting content.
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi_Int[cpsi]) using numeric integrator RooIntegrator1D to calculate Int(cpsi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x560877ab9f10 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi for nset (cpsi) with code 0 from preexisting content.
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi_Int[cpsi]) using numeric integrator RooIntegrator1D to calculate Int(cpsi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087a9575c0 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi for nset (cpsi) with code 0 from preexisting content.
[#1] INFO:Fitting -- RooAbsPdf::fitTo(Mf_over_Mf_Int[cpsi]) fixing normalization set for coefficient determination to observables in data
[#1] INFO:Fitting -- RooAddition::defaultErrorLevel(nll_Mf_over_Mf_Int[cpsi]_MfData) Summation contains a RooNLLVar, using its error level
[#1] INFO:Minimization -- RooAbsMinimizerFcn::setOptimizeConst: activating const optimization
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087aa12340 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[cpsi] for nset () with code 1 from preexisting content.
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Mf_Int[cpsi]) using numeric integrator RooIntegrator1D to calculate Int(cpsi)
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Minimization -- RooAbsMinimizerFcn::setOptimizeConst: deactivating const optimization
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_Int[psi]) using numeric integrator RooIntegrator1D to calculate Int(psi)
[#1] INFO:Caching -- RooAbsCachedPdf::getCache(Mf) creating new cache 0x56087aa12340 with pdf Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi for nset (cpsi) with code 0
[#1] INFO:NumericIntegration -- RooRealIntegral::init(Tpsi_CONV_Rpsi_CACHE_Obs[cpsi]_NORM_cpsi_Int[cpsi]) using numeric integrator RooIntegrator1D to calculate Int(cpsi)
[#1] INFO:NumericIntegration -- RooRealIntegral::init(T_Int[cpsi]) using numeric integrator RooIntegrator1D to calculate Int(cpsi)

Date: February 2018

Authors: Clemens Lange, Wouter Verkerke (C version)

Definition in file rf210_angularconv.py.