Rf 9 0 1_Numintconfig

Numeric algorithm tuning: configuration and customization of how numeric (partial) integrals are executed

Author: Clemens Lange, Wouter Verkerke (C++ version)
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Wednesday, January 19, 2022 at 10:39 AM.

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from __future__ import print_function
import ROOT

Adjust global 1D integration precision

Print current global default configuration for numeric integration strategies

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Example: Change global precision for 1D integrals from 1e-7 to 1e-6

The relative epsilon (change as fraction of current best integral estimate) and absolute epsilon (absolute change w.r.t last best integral estimate) can be specified separately. For most pdf integrals the relative change criterium is the most important, however for certain non-pdf functions that integrate out to zero a separate absolute change criterium is necessary to declare convergence of the integral

NB: ROOT.This change is for illustration only. In general the precision should be at least 1e-7 for normalization integrals for MINUIT to succeed.

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Numeric integration of landau pdf

Construct pdf without support for analytical integrator for demonstration purposes

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x = ROOT.RooRealVar("x", "x", -10, 10)
landau = ROOT.RooLandau("landau", "landau", x, ROOT.RooFit.RooConst(0), ROOT.RooFit.RooConst(0.1))

Activate debug-level messages for topic integration to be able to follow actions below

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ROOT.RooMsgService.instance().addStream(ROOT.RooFit.DEBUG, Topic=ROOT.RooFit.Integration)

Calculate integral over landau with default choice of numeric integrator

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intLandau = landau.createIntegral({x})
val = intLandau.getVal()
print(" [1] int_dx landau(x) = ", val)  # setprecision(15)

Same with custom configuration

Construct a custom configuration which uses the adaptive Gauss-Kronrod technique for closed 1D integrals

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customConfig = ROOT.RooNumIntConfig(ROOT.RooAbsReal.defaultIntegratorConfig())
integratorGKNotExisting = customConfig.method1D().setLabel("RooAdaptiveGaussKronrodIntegrator1D")
if integratorGKNotExisting:
    print("WARNING: RooAdaptiveGaussKronrodIntegrator is not existing because ROOT is built without Mathmore support")

Calculate integral over landau with custom integral specification

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intLandau2 = landau.createIntegral({x}, NumIntConfig=customConfig)
val2 = intLandau2.getVal()
print(" [2] int_dx landau(x) = ", val2)

Adjusting default config for a specific pdf

Another possibility: associate custom numeric integration configuration as default for object 'landau'

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Calculate integral over landau custom numeric integrator specified as object default

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intLandau3 = landau.createIntegral({x})
val3 = intLandau3.getVal()
print(" [3] int_dx landau(x) = ", val3)

Another possibility: Change global default for 1D numeric integration strategy on finite domains

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if not integratorGKNotExisting:

    # Adjusting parameters of a speficic technique
    # ---------------------------------------------------------------------------------------

    # Adjust maximum number of steps of ROOT.RooIntegrator1D in the global
    # default configuration
    ROOT.RooAbsReal.defaultIntegratorConfig().getConfigSection("RooIntegrator1D").setRealValue("maxSteps", 30)

    # Example of how to change the parameters of a numeric integrator
    # (Each config section is a ROOT.RooArgSet with ROOT.RooRealVars holding real-valued parameters
    #  and ROOT.RooCategories holding parameters with a finite set of options)
    customConfig.getConfigSection("RooAdaptiveGaussKronrodIntegrator1D").setRealValue("maxSeg", 50)
    customConfig.getConfigSection("RooAdaptiveGaussKronrodIntegrator1D").setCatLabel("method", "15Points")

    # Example of how to print set of possible values for "method" category