Hello,

Looking at https://github.com/clelange/roofit, I see that rf105_funcbinding.py isn’t working (tried it locally on lxplus and it isn’t indeed). Is there a chance to make it operational or at least to see how the Math::beta_pdf can be used in python?

I’m talking about this line:

`beta = ROOT.RooFit.bindPdf("beta", ROOT.Math.beta_pdf, x2, a, b)`

Thanks!

Noam

Hi,

The function ROOT.Math.beta_pdf should work in Python. The problem you are having is maybe due to calling ROOT.RooFit.bindPdf in PyROOT. Maybe @etejedor can help you on this

Best Regards

Lorenzo

Hi,

function pointers are currently not supported.

We opened an issue on our bug tracker about this https://sft.its.cern.ch/jira/browse/ROOT-9159

Best,

Danilo

Hi Lorenzo and Danilo,

Many Thanks for the super prompt response!

I guess there isn’t any quick and dirty workaround I can try in the meantime?

Cheers,

Noam

Hi Noam,

actually there is, passing through C++ and finding back the elements in Python:

```
# Bind one-dimensional ROOT.TMath.Erf function as ROOT.RooAbsReal function
ROOT.gInterpreter.ProcessLine('auto x = RooRealVar("x", "x", -3, 3); auto myerf = RooFit::bindFunction("erf", TMath::Erf, x)')
x = ROOT.x
erf = ROOT.myerf
```

Could this unblock you?

Cheers,

D

Thanks Danilo, I think that should do the work

Cheers,

Noam

Hi Danilo,

Just to say that in order for this to work, one needs to explicitly load the RooFit lib:

`import ROOT`

`from ROOT import *`

`ROOT.gSystem.Load("libRooFit")`

`ROOT.gInterpreter.ProcessLine(...)`

and the rest is as you had above

Cheers,

Noam

Hi @dpiparo

Just one small question

How do I release the definition of `x`

and `myerrf`

from ROOT if this actually has to be done in a loop?

Sorry about the spam!

Noam

Thanks. What version are you using?

Hi Noam,

don’t worry: this is a valid question. What do you exactly mean? Are you having problems in redefining something in C++?

Cheers,

D

Hi Danilo,

- I’m using RooFit v3.60
- About the other question, I run this in a loop and the definitions done in the ProcessLine() call are staying across the loop, unlike the definitions done with everything that can be simply defined in pyROOT (e.g. y=RooRealVar(…)). At least, I think this is the case.

The error I get is`error: redefinition of 'x'... previous definition is here...`

So, I guess I will need to “unbind” x and myerrf somehow from ROOT in every iteration but I don’t know how.

Cheers,

Noam

Hi Noam,

thanks.

About point 1) what is the ROOT version?

About point 2) What about defining the x variable outside the loop?

Cheers,

D

Hi Danilo,

I’m using ROOT 6.08/06.

About defining the x variable once, that’s not an option since the range has to change in different iterations.

Is it possible to undefine/unbind it?

Cheers,

Noam

Hi Danilo,

I think I managed:

```
cpp = 'auto x = RooRealVar("x","",'+str(xmin)+','+str(xmax)+'); x.setBins('+str(nbins)+'); auto myerrf = RooFit::bindFunction("errf", TMath::Erf, x);'
if(not isFirstIter): cpp = cpp.replace("auto","")
print "cpp:",cpp
ROOT.gInterpreter.ProcessLine(cpp)
response = ROOT.x
errf = ROOT.myerrf
...
```

Cheers,

Noam

Hi Noam,

I see: this would work. Thanks for sharing the solution. The name of the game is indeed to avoid idiosyncrasies which could pop up in the mix of Python and C++ such as redefinition of variables.

In order to reuse the same memory and avoid to reallocate a new RooRealVar at every iteration, you may want to use the RooRealVar methods setMin, setMax, setBins.

Cheers,

Danilo

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