docs: def pdf(self):
          """
          Returns the probability density function(pdf).
  
          Returns
          -------
          function: The probability density function of the distribution.
  
          Examples
          --------
          >>> from pgmpy.factors.distributions import GaussianDistribution
          >>> dist = GD(variables=['x1', 'x2', 'x3'],
          ...           mean=[1, -3, 4],
          ...           cov=[[4, 2, -2],
          ...                [2, 5, -5],
          ...                [-2, -5, 8]])
          >>> dist.pdf
          <function pgmpy.factors.distributions.GaussianDistribution.GaussianDistribution.pdf.<locals>.<lambda>>
          >>> dist.pdf([0, 0, 0])
          0.0014805631279234139
          """
          return lambda *args: multivariate_normal.pdf(
              args, self.mean.reshape(1, len(self.variables))[0], self.covariance)