code: def logpdf(self, x):
      # TODO: replace this
      return np.log(self.pdf(x))
  
imports: import numpy
  from scipy import special
  from statsmodels.sandbox.distributions.multivariate import mvstdtprob
  from .extras import mvnormcdf
label_desc: Use image node_id 4 for calling the BivariateNormal obj's underlying member method code with example usage: obj.logpdf(x) and returns: np