class RooSimPdfBuilder: public TObject

This tool has now been superceded by RooSimWSTool Begin_Html >

RooSimPdfBuilder is a powerful tool to build RooSimultaneous PDFs that are defined in terms component PDFs that are identical in structure, but have different parameters.

Example

The following example demonstrates the essence of RooSimPdfBuilder: Given a dataset D with a RooRealVar X and a RooCategory C that has state C1 and C2.

• We want to fit the distribution of X with a Gaussian+ArgusBG PDF,
• We want to fit the data subsets D(C==C1) and D(C==C2) separately and simultaneously.
• The PDFs to fit data subsets D_C1 and D_C2 are identical except for
  • the kappa parameter of the ArgusBG PDF and
  • the sigma parameter of the gaussian PDF
  where each PDF will have its own copy of the parameter

Coding this example directly with RooFit classes gives (we assume dataset D and variables C and X have been declared previously)

 RooRealVar m("m","mean of gaussian",-10,10) ;
 RooRealVar s_C1("s_C1","sigma of gaussian C1",0,20) ;
 RooRealVar s_C2("s_C2","sigma of gaussian C2",0,20) ;
 RooGaussian gauss_C1("gauss_C1","gaussian C1",X,m,s_C1) ;
 RooGaussian gauss_C2("gauss_C2","gaussian C2",X,m,s_C2) ;
 RooRealVar k_C1("k_C1","ArgusBG kappa parameter C1",-50,0) ;
 RooRealVar k_C2("k_C2","ArgusBG kappa parameter C2",-50,0) ;
 RooRealVar xm("xm","ArgusBG cutoff point",5.29) ;
 RooArgusBG argus_C1("argus_C1","argus background C1",X,k_C1,xm) ;
 RooArgusBG argus_C2("argus_C2","argus background C2",X,k_C2,xm) ;
 RooRealVar gfrac("gfrac","fraction of gaussian",0.,1.) ;
 RooAddPdf pdf_C1("pdf_C1","gauss+argus_C1",RooArgList(gauss_C1,argus_C1),gfrac) ;
 RooAddPdf pdf_C2("pdf_C2","gauss+argus_C2",RooArgList(gauss_C2,argus_C2),gfrac) ;
 RooSimultaneous simPdf("simPdf","simPdf",C) ;   
 simPdf.addPdf(pdf_C1,"C1") ;
 simPdf.addPdf(pdf_C2,"C2") ;
  

Coding this example with RooSimPdfBuilder gives

 RooRealVar m("m","mean of gaussian",-10,10) ;
 RooRealVar s("s","sigma of gaussian",0,20) ;
 RooGaussian gauss("gauss","gaussian",X,m,s) ;
 RooRealVar k("k","ArgusBG kappa parameter",-50,0) ;
 RooRealVar xm("xm","ArgusBG cutoff point",5.29) ;
 RooArgusBG argus("argus","argus background",X,k,xm) ;
 RooRealVar gfrac("gfrac","fraction of gaussian",0.,1.) ;
 RooAddPdf pdf("pdf","gauss+argus",RooArgList(gauss,argus),gfrac) ;
 RooSimPdfBuilder builder(pdf) ;
 RooArgSet* config = builder.createProtoBuildConfig() ;
 (*config)["physModels"] = "pdf" ;      // Name of the PDF we are going to work with
 (*config)["splitCats"]  = "C" ;        // Category used to differentiate sub-datasets
 (*config)["pdf"]        = "C : k,s" ;  // Prescription to taylor PDF parameters k and s 
                                        // for each data subset designated by C states
 RooSimultaneous* simPdf = builder.buildPdf(*config,&D) ;
  

The above snippet of code demonstrates the concept of RooSimPdfBuilder: the user defines a single 'prototype' PDF that defines the structure of all PDF components of the RooSimultaneous PDF to be built. RooSimPdfBuilder then takes this prototype and replicates it as a component PDF for each state of the C index category.

In the above example RooSimPdfBuilder will first replicate k and s into k_C1,k_C2 and s_C1,s_C2, as prescribed in the configuration. Then it will recursively replicate all PDF nodes that depend on the 'split' parameter nodes: gauss into gauss_C1,C2, argus into argus_C1,C2 and finally pdf into pdf_C1,pdf_C2. When PDFs for all states of C have been replicated they are assembled into a RooSimultaneous PDF, which is returned by the buildPdf() method.

Although in this very simple example the use of RooSimPdfBuilder doesn't reduce the amount of code much, it is already easier to read and maintain because there is no duplicate code. As the complexity of the RooSimultaneous to be built increases, the advantages of RooSimPdfBuilder will become more and more apparent.

Builder configuration rules for a single prototype PDF

Each builder configuration needs at minumum two lines, physModels and splitCats, which identify the ingredients of the build. In this section we only explain the building rules for builds from a single prototype PDF. In that case the physModels line always reads

  physModels = {pdfName}
  

The second line, splitCats, indicates which categories are going to be used to differentiate the various subsets of the 'master' input data set. You can enter a single category here, or multiple if necessary:

 splitCats = {catName} [{catName} ...]
  

All listed splitcats must be RooCategories that appear in the dataset provided to RooSimPdfBuilder::buildPdf()

The parameter splitting prescriptions, the essence of each build configuration can be supplied in a third line carrying the name of the pdf listed in physModels

 pdfName = {splitCat} : {parameter} [,{parameter},....]
  

Each pdf can have only one line with splitting rules, but multiple rules can be supplied in each line, e.g.

 pdfName = {splitCat} : {parameter} [,{parameter},....] 
           {splitCat} : {parameter} [,{parameter},....]
  

Conversely, each parameter can only have one splitting prescription, but it may be split by multiple categories, e.g.

 pdfName = {splitCat1},{splitCat2} : {parameter}
  

instructs RooSimPdfBuilder to build a RooSuperCategory of {splitCat1} and {splitCat2} and split {parameter} with that RooSuperCategory

Here is an example of a builder configuration that uses several of the options discussed above:

   physModels = pdf
   splitCats  = tagCat runBlock
   pdf        = tagCat          : signalRes,bkgRes 
                runBlock        : fudgeFactor      
                tagCat,runBlock : kludgeParam
  

How to enter configuration data

The prototype builder configuration returned by RooSimPdfBuilder::createProtoBuildConfig() is a pointer to a RooArgSet filled with initially blank RooStringVars named physModels,splitCats and one additional for each PDF supplied to the RooSimPdfBuilders constructor (with the same name)

In macro code, the easiest way to assign new values to these RooStringVars is to use RooArgSets array operator and the RooStringVars assignment operator, e.g.

 (*config)["physModels"] = "Blah" ;
  

To enter multiple splitting rules simply separate consecutive rules by whitespace (not newlines), e.g.

 (*config)["physModels"] = "Blah " // << note trailing space here
                          "Blah 2" ;
  

In this example, the C++ compiler will concatenate the two string literals (without inserting any whitespace), so the extra space after 'Blah' is important here.

Alternatively, you can read the configuration from an ASCII file, as you can for any RooArgSet using RooArgSet::readFromFile(). In that case the ASCII file can follow the syntax of the examples above and the '\\' line continuation sequence can be used to fold a long splitting rule over multiple lines.

 RooArgSet* config = builder.createProtoBuildConfig() ;
 config->readFromFile("config.txt") ;
 --- config.txt ----------------    
 physModels = pdf
 splitCats  = tagCat
 pdf        = tagCat : bogusPar
 -------------------------------
  

Working with multiple prototype PDFs

It is also possible to build a RooSimultaneous PDF from multiple PDF prototypes. This is appropriate for cases where the input prototype PDF would otherwise be a RooSimultaneous PDF by itself. In such cases we don't feed a single RooSimultaneous PDF into RooSimPdfBuilder, instead we feed it its ingredients and add a prescription to the builder configuration that corresponds to the PDF-category state mapping of the prototype RooSimultaneous.

The constructor of the RooSimPdfBuilder will look as follows:

  RooSimPdfBuilder builder(RooArgSet(pdfA,pdfB,...)) ;
  

The physModels line is now expanded to carry the pdf->state mapping information that the prototype RooSimultaneous would have. I.e.

 physModels = mode : pdfA=modeA  pdfB=modeB
  

is equivalent to a prototype RooSimultaneous constructed as

 RooSimultanous simPdf("simPdf","simPdf",mode);
 simPdf.addPdf(pdfA,"modeA") ;
 simPdf.addPdf(pdfB,"modeB") ;
  

The rest of the builder configuration works the same, except that each prototype PDF now has its own set of splitting rules, e.g.

 physModels = mode : pdfA=modeA  pdfB=modeB
 splitCats  = tagCat
 pdfA       = tagCat : bogusPar
 pdfB       = tagCat : fudgeFactor   
  

Please note that

• The master index category ('mode' above) doesn't have to be listed in splitCats, this is implicit.
• The number of splitting prescriptions goes by the number of prototype PDFs and not by the number of states of the master index category (mode in the above and below example).

In the following case:

    physModels = mode : pdfA=modeA  pdfB=modeB  pdfA=modeC  pdfB=modeD
  

there are still only 2 sets of splitting rules: one for pdfA and one for pdfB. However, you can differentiate between modeA and modeC in the above example. The technique is to use mode as splitting category, e.g.

    physModels = mode : pdfA=modeA  pdfB=modeB  pdfA=modeC  pdfB=modeD
    splitCats = tagCat
    pdfA      = tagCat : bogusPar 
                mode   : funnyPar
    pdfB      = mode   : kludgeFactor
  

will result in an individual set of funnyPar parameters for modeA and modeC labeled funnyPar_modeA and funnyPar_modeB and an individual set of kludgeFactor parameters for pdfB, kludgeFactor_modeB and kludgeFactor_modeD. Please note that for splits in the master index category (mode) only the applicable states are built (A,C for pdfA, B,D for pdfB)

Advanced options

Partial splits

You can request to limit the list of states of each splitCat that will be considered in the build. This limitation is requested in the each build as follows:

 splitCats = tagCat(Lep,Kao) RunBlock(Run1)
  

In this example the splitting of tagCat is limited to states Lep,Kao and the splitting of runBlock is limited to Run1. The splits apply globally to each build, i.e. every parameter split requested in this build will be limited according to these specifications.

NB: Partial builds have no pdf associated with the unbuilt states of the limited splits. Running such a pdf on a dataset that contains data with unbuilt states will result in this data being ignored completely.

Non-trivial splits

It is possible to make non-trivial parameter splits with RooSimPdfBuilder. Trivial splits are considered simple splits in one (fundamental) category in the dataset or a split in a RooSuperCategory 'product' of multiple fundamental categories in the dataset. Non-trivial splits can be performed using an intermediate 'category function' (RooMappedCategory, RooGenericCategory,RooThresholdCategory etc), i.e. any RooAbsCategory derived objects that calculates its output as function of one or more input RooRealVars and/or RooCategories.

Such 'function categories' objects must be constructed by the user prior to building the PDF. In the RooSimPdfBuilder::buildPdf() function these objects can be passed in an optional RooArgSet called 'auxiliary categories':

   const RooSimultaneous* buildPdf(const RooArgSet& buildConfig, const RooAbsData* dataSet, 
                                   const RooArgSet& auxSplitCats, Bool_t verbose=kFALSE) {
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  

Objects passed in this argset can subsequently be used in the build configuration, e.g.

 RooMappedCategory tagMap("tagMap","Mapped tagging category",tagCat,"CutBased") ;
 tagMap.map("Lep","CutBased") ;
 tagMap.map("Kao","CutBased") ;
 tagMap.map("NT*","NeuralNet") ;                                                                                          
 ...
 builder.buildPdf(config,D,tagMap) ;
                          ^^^^^^

   physModels = pdf
   splitCats  = tagCat runBlock
   pdf        = tagCat          : signalRes 
                tagMap          : fudgeFactor      
                ^^^^^^
  

In the above example signalRes will be split in signalRes_Kao,signalRes_Lep, signalRes_NT1,signalRes_NT2, while fudgeFactor will be split in fudgeFactor_CutBased and fudgeFactor_NeuralNet.

Category functions passed in the auxSplitCats RooArgSet can be used regularly in the splitting configuration. They should not be listed in splitCats, but must be able to be expressed completely in terms of the splitCats that are listed.

Multiple connected builds

Sometimes you want to build multiple PDFs for independent consecutive fits that share some of their parameters. For example, we have two prototype PDFs pdfA(x;p,q) and pdfB(x;p,r) that have a common parameter p. We want to build a RooSimultaneous for both pdfA and B, which involves a split of parameter p and we would like to build the simultaneous pdfs simA and simB such that still share their (now split) parameters p_XXX. This is accomplished by letting a single instance of RooSimPdfBuilder handle the builds of both pdfA and pdfB, as illustrated in this example:

 RooSimPdfBuilder builder(RooArgSet(pdfA,pdfB)) ;
 RooArgSet* configA = builder.createProtoBuildConfig() ;
 (*configA)["physModels"] = "pdfA" ;     
 (*configA)["splitCats"]  = "C" ;        
 (*configA)["pdf"]        = "C : p" ;  
 RooSimultaneous* simA = builder.buildPdf(*configA,&D) ;
 RooArgSet* configB = builder.createProtoBuildConfig() ;
 (*configA)["physModels"] = "pdfB" ;     
 (*configA)["splitCats"]  = "C" ;        
 (*configA)["pdf"]        = "C : p" ;  
 RooSimultaneous* simB = builder.buildPdf(*configB,&D) ;
  

Ownership of constructed PDFs

The RooSimPdfBuilder instance owns all the objects it creates, including the top-level RooSimultaneous returned by buildPdf(). Therefore the builder instance should exist as long as the constructed PDFs needs to exist.

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