Using python functions into RooFit

[guiguem]

The recommended method to use custom pdf is to use C++ and Phylloxera.
However it should be possible to bind a python function too.
Here is a nasty but working example on how to generate a RooFit pdf from a python function:

class RosenBrock(ROOT.TPyMultiGenFunction):
    def __init__( self ):
        print("CREATED")
        ROOT.TPyMultiGenFunction.__init__( self, self )

    def NDim( self ):
        print('PYTHON NDim called')
        return 2
    def __call__(self,args):
        x = args[0]
        y = args[1];
        tmp1 = y-x*x;
        tmp2 = 1-x;
        return 100*tmp1*tmp1+tmp2*tmp2;


if __name__ == "__main__":
    rose = RosenBrock()
    f = ROOT.TPyMultiGenFunction(rose)
    x = ROOT.RooRealVar("x","x",0,10)
    a = ROOT.RooRealVar("a","a",1,2)
    fx = ROOT.RooFit.bindFunction("test",f, ROOT.RooArgList(x, a))

We should be able to adapt this to just need to import the function from the right module and integrate it into a RooFit processor.

[guiguem]

Solved in morpho morphoorg/morpho#141