def _num_integral(self, r, c):
        """
        numerical integral (1-e^{-c*x^2})/x dx [0..r]
        :param r: radius
        :param c: 1/2sigma^2
        :return:
        """
        out = integrate.quad(lambda x: (1-np.exp(-c*x**2))/x, 0, r)
        return out[0]
def _num_integral ( self , r , c ) : out = integrate . quad ( lambda x : ( 1 - np . exp ( - c * x ** 2 ) ) / x , 0 , r ) return out [ 0 ]
numerical integral (1-e^{-c*x^2})/x dx [0..r]
        :param r: radius
        :param c: 1/2sigma^2
        :return: