code: def pdf_new(self, x, mu, sigma, skw):
          
          if skw > 1 or skw < -1:
              print("skewness %s out of range" % skw)
              skw = 1.
          e, w, a = self.map_mu_sigma_skw(mu, sigma, skw)
          pdf = self.pdf(x, e, w, a)
          return pdf
docs: function with different parameterisation
          :param x:
          :param mu: mean
          :param sigma: sigma
          :param skw: skewness
          :return: