def genBgTerm(self,vTot=0.5,vCommon=0.1,pCausal=0.5,XX=None,use_XX=False,a=None,c=None,plot=False):
        """ generate  """
        if use_XX:
            if XX is None:  XX = self.XX
            assert XX is not None, 'Simulator: set XX!'
            Yc,Yi = self._genBgTerm_fromXX(vTot,vCommon,XX,a=a,c=c)
        else:
            Yc,Yi = self._genBgTerm_fromSNPs(vTot=vTot,vCommon=vCommon,pCausal=pCausal,plot=plot)
        return Yc, Yi