//takes a varname which is supposed to represent a RooAbsReal in
//the m_rws (RooWorkspace) member of the class.
//changes it to a RooFormulaVar.
//formula is used in the constructor of this RooFormulaVar
//and dependents is a comma-separated list of other RooAbsReal
//objects that are also present in m_rws upon which the RooFormulaVar
//is dependent.
void RooSimultaneousFitter::AddConstraint(const char* varname,
                                          const char* formula,
                                          const char* dependents)
{  
  //put dependents names in a vector
  std::vector<std::string> dependents_vec;
  std::string dummy = (std::string)dependents;  
  boost::split(dependents_vec,dummy,boost::is_any_of(","));
  
  RooArgList depList;
  
  //m_rws is a RooWorkspace member of the class
  
  RooAbsReal* var;
  for (std::vector<std::string>::iterator iter = dependents_vec.begin();
       iter != dependents_vec.end(); iter++){
    var = (RooAbsReal*)m_rws->obj(iter->c_str());
    depList.add(*var);
  }
  //checking that the var we are constraining is there
  var = (RooAbsReal*)m_rws->obj(varname);
  
  //make the rooformulavar
  std::stringstream newname;
  newname << varname << "_function";
  RooFormulaVar function(newname.str().c_str(),"",formula,depList);
  
  //import it first since import clones the object and to get the address of
  //it in the RooWorkspace one must get it again (I think)
  m_rws->import(function);
  
  RooAbsReal* newvar = (RooAbsReal*)m_rws->obj(newname.str().c_str());
  
  //transfer the relationships of the old var to the new one.
  TIterator* iter = var->clientIterator();
  RooAbsArg* client;
  
  while( (client=(RooAbsArg*)iter->Next()) ){
    client->replaceServer(*var,*newvar,kTRUE,kTRUE);
  }
  delete iter;
  
  return;
  
}