def _cauchy_ ( self , mu , gamma ) :
    """Generate Cauchy random numbers 
    - rely on the distribution of the ratio for two Gaussian variables 
    - see https://en.wikipedia.org/wiki/Cauchy_distribution
    """
    g1 = self.gauss ( 0.0 , 1.0 )
    while abs ( g1 ) < _fmin : g1 = self.gauss ( 0.0 , 1.0 )
    g2 = self.gauss ( 0.0 , 1.0 )
    return 1.0 * mu + ( 1.0 * g2 / g1 ) * gamma