Re: [ROOT] On the ability of RooFit to use an arbitrary fitter plugin

[Rene Brun <Rene.Brun@cern.ch>]

Hi Wouter,

Could you meet with Lorenzo and me next time you come to CERN?
We have already discussed the extension to the TVirtualFitter
and have to discuss with you the use of this interface as well as
some other changes.

Rene


On Fri, 
27 
Jan 2006, Wouter Verkerke wrote:

> Hi,
>
> I agree with Rene's proposal (i.e revise TVirtualFitter first).
>
> Class RooMinuit was written a long time ago, when minuit was for all
> practical purposes the only available fitter engine. Since the
> TVirtualFitter interface did not provide access to essential information
> at that time I took from the guts of gMinuit directly, just to make it
> work. That more or less explains the current situation.
>
> I'd be especially happy if I could move to an official interface to
> retrieve the various bits of information on the correlation matrix.
> (Perhaps this is already possible, I have not checked recently.) Rewriting
> the minimizer-RooFit interface has been on my to-do list for a while but
> if there is going to be some movement in this area, I make this a higher
> priority.
>
> In the end I envision a RooFit interface class for each of the minimizer
> implementations in ROOT so RooFit users have access to each of the
> minimizers specific functionality (e.g. minos, hesse in minuit) and put
> them all under a RooFit 'mimimizer interface' base class that takes care
> of the common functionality as is seen through ROOT class
> TVirtualFitter.
>
> 						Wouter
>
>
>
>
>
>
>
> On Fri, 27 Jan 2006, Christian Holm Christensen wrote:
>
> > Hi Kevin, Rene, Wouter, et al,
> >
> > [Sorry for the late follow-up - I've been busy as ...]
> >
> > On Wed, 2006-01-25 at 16:39 -0500, Kevin B. McCarty wrote:
> > > [CC-ing to Chris Roat and debian-science since I originally suggested
> > > there that RooFit could be patched to use any of the fitter plugins.]
> > >
> > > Unfortunately it looks like RooMinuit.cxx and RooFitResults.cxx can't
> > > currently be converted to use the TVirtualFitter interface.  There are
> > > two main issues:
> > >
> > > 1) The function RooMinuit::contour() directly uses TMinuit::Contour(), a
> > > method which isn't accessible through TVirtualFitter (or even in TFitter).
> >
> > Hmph.
> >
> > > 2) The function RooFitResult::fillCorrMatrix() mucks about in the
> > > internals of the TMinuit class in order to obtain an error correlation
> > > matrix.  There is no API for obtaining this matrix even in TMinuit, let
> > > alone in TVirtualFitter.
> >
> > Whoha - those guys must have nerves of steel :-)
> >
> > > I could submit a patch to fix RooFitResult::lastMinuitFit() and
> > > RooMinuit::synchronize() to use TVirtualFitter instead of gMinuit, but I
> > > guess there is not much point until (1) and (2) above are dealt with.
> > > Someday maybe these functionalities can be added to TVirtualFitter (and
> > > the classes that inherit from it) and RooFit can switch to use it
> > > completely.
> > ...
> > > To conclude, currently libRooFit is constrained to depend specifically
> > > upon libMinuit.  I do apologize for wasting people's time because I
> > > thought otherwise at first.  For the ROOT Debian packages, I think
> > > therefore libRooFit cannot be packaged as a library unless libMinuit is
> > > also packaged as a library.  Or, they could both be packaged just as
> > > plugins.
> >
> > To the ROOT people that get this mail:  I think many developers are not
> > really aware of the various abstract interface that exist in ROOT, like
> > TVirtualFitter, TSQLServer, and so on.  That results in people writing
> > code like
> >
> > 	TSQLServer* s = TMySQLServer::Connect(...)
> >
> > (fictive example :-) which breaks these nice interfaces, and makes life
> > hard for the user.
> >
> > Perhaps you could make an effort to stipulate that the virtual
> > interfaces are there, and should be used.   Thanks.
> >
> > Of course, the Right Way(tm) to do it, would be to _not_ export the
> > declarations of pure `plug-in' classes like `TMinuit', `TMySQLServer',
> > and so on.   That is, do not install the header files anywhere, nor
> > create development libraries, and put the binary loadable plug-in
> > modules somewhere the linker doesn't look for it, say
> > `<base>/lib/root/plugins'.
> >
> > For the Debian people:  I'll probably merge Minuit into the libroot
> > package, or make libroot-minuit and libroot-minuit-dev.   Making rootfit
> > a plug-in package wouldn't work.
> >
> > Yours,